eForth for cheap STM8S gadgets

Turn cheap stuff from AliExpress into interactive development kits!

Similar projects worth following
TG9541/STM8EF is based on Dr. C.H. Ting's STM8 eForth (a basic eForth in 5.5K Flash compiling to RAM). For 20ct STM8S µCs with 8K Flash the core had to be much smaller.

A lot of features were added: background task, Forth interrupt handlers, vectored I/O, 7S-LED display drivers, analog and digital I/O, board support (e.g. W1209), and a configuration framework with feature selection.

STM8 eForth uses the SDCC tool chain: C can be mixed with Forth, e.g. as a shell for testing, parameter setting, or for scripting.

Currently the project targets usability: e4thcom as a programming environment, and automated tests with Docker and Travis-CI, and a library.

What is it?

STM8 eForth is among the smallest user friendly Forth systems for µCs: it brings best of early 1990s style Forth to low-cost contemporary embedded control. Focusing in usability, this project delivers configurable board support code for selected low cost targets and docs. STM8 eForth uses very little memory yet it has a long feature list. A small but active community ensures that using it for new projects is easy!

The code and binaries on GitHub can be used in many ways:

  • as an alternative firmware Chinese commodity boards (e.g. thermostats, DCDC converters, or relay boards)
  • for embedded systems with an interactive shell (scriptable and extensible)
  • for creating smart SPI, I2C, or RS232 smart sensors with a scripting shell, e.g. for RaspberryPi, Arduino, or ESP8266
  • as an interactive environment for exploring the STM8 architecture
  • for learning Forth. It's easy and fun - find out why in the text below!
  • ...

Why a Forth for Cheap Chinese boards?

Because it's fun: cheap mass-produced imperfection is a playground for creativity :-)

Right now, the W1209 is my favorite target: it's a rather complete embedded control board with a UI at a very good price. It's as cheap as it looks, and the challenge is in it's imperfections: the guy who designed the board clearly didn't have a connected application in mind, and I had a lot of fun making it do things it was never intended to do.

There are challenges, like the lack of communication ports. The "sensor connector" can either be used as a a 2-wire RS232 "bus" or for sensing. What if you need sensing and communication at the same time?  The project provides also provides a binary for full-duplex 3-wire RS232 through the key pins (while keeping the keys functional). A plug-in system makes it easy to test new ideas, like using the "update connector" can be used as a home brew field bus interface!

Which target boards are supported?

Besides generic CORE target for STM8S001, STM8S103 and STM8S105, there is currently support for the following boards:

Some more boards are supported on request, e.g.

@Elliot Williams worked on using the ESP-14 as an IoT deviced(the ESP-14 is an ESP8266 with an STM8S003F3P6 in a ESP-12 package).

Programmable power supplies based on theXH-M188, and a cheap DC/DC converter are work in progress. There are also several types of STM8S003F3 based voltmeters that can be supported.

Read more about likely future targets below.

Why Forth?

Again, because it's fun!

Consider this:

  • compared to other programming environments the core of Forth is easy to fully understand
  • like Lisp, Forth has a REPL (Read-Evaluate-Print-Loop) which enables software testing in a way impossible with "Edit-Compile-Run-Debug" (e.g. Arduino)
  • it's easy to build Domain Specific Languages (you can literally program the compiler!)
  • the stack-centered "factoring" approach provides implicit data flow which leads to maintainable code
  • Interpreter-compiler, basic OS functions fit in just 4K code :-)

Forth starts out as a stack machine with a tiny instruction set and minimal hardware requirements. It fits in a few KiB, and the target, even a lowly µC, can even be used as the development system. The Forth stack machine is a minimalistic VM on a standard CPU, but there are also hardware implementations (e.g. for FPGAs, or a 144 core Forth processor). The VM is ideal for fast context switching and Forth easily meets hard-real-time requirements. It's no surprise...

Read more »

Original version of STM8EFalong with docs as received from Dr. C.H. Ting on 21/Nov/2016. The docs are worth reading, the eForth binary will run on the STM8S Discovery.

Zip Archive - 21.97 kB - 11/21/2016 at 20:13


  • 1 × ST-Link V2 ICP adapter (e.g. $2.00 from AliExpress) The ST-Link on an STM8S Discovery Board can be used, too
  • 1 × serial interface /w 3.3V level (e.g. a $0.60 CH340 USB adapter) e.g a CH340 USB interface
  • 1 × STM8S target device as listed in the GitHub Wiki (e.g. a $0.70 "STM8S103F3P6 minimal system board") e.g. "STM8S103F3P6 STM8S development board" from your favorite China source
  • 1 × Some headers, patchwires, breadboard etc (about $2.00)

  • STM8 eForth at the German Forth Conference

    Thomasa day ago 0 comments

    The German Forth Conference is one of the better known venues in the international Forth scene. It will take place from 5 to 8 April 2018 in the Linuxhotel in Essen-Horst. The list of talks is here.

    Manfred Mahlow will talk about WORDLIST, a name-space-like approach in Forth, and demonstrate it with two µC Forth implementations, one of which, I've heard, might be STM8 eForth (at least, it's part of the STM8 eForth release 2.2.21).

    In a second talk, Manfred Mahlow will introduce STM8 eForth as a "semi-tethered" Forth, one that combines an embedded console with PC-side code. If you've followed this project on HaD, the idea should be familiar.

  • STM8 eForth 2.2.21: New features, Improvements, and Bug-Fixes

    Thomas03/05/2018 at 21:21 0 comments

    The new release STM8 eForth 2.2.21 brings so many new features, improvements, and also bug-fixes, that it would be exceedingly boring to name them all. Some stuff is actually quite interesting :-)

    By the way, yesterday I started working on 2.2.22,pre, and the first preview already contains experimental support for STM8S High Density devices. STM8 eForth now runs on a chip with 6K RAM and 128K flash memory (remember that STM8 eForth works quite well on chips with 1K RAM and 8K flash). Only the lower 32K portion is directly usable for compiled Forth code but, given the density of Forth code, that's a lot.

  • STM8 eForth 2.2.21.pre4: more features, same size

    Thomas02/25/2018 at 16:31 0 comments

    ... and a bug fix: in one of the former STM8 eForth 2.2.21-pre-releases WORDS got broken. It didn't show the RAM dictionary when in NVM mode! This is now fixed.

    A major improvement is the implementation of WIPE, something similar to COLD, but only targeting the dictionary in RAM. WIPE gets called during start-up, and besides resetting the dictionary, it creates a dummy word, that makes using MARKER much easier.

    #require WIPE creates an ALIAS word, which, if loaded into RAM, will reinitialize the dictionary (and remove itself if it was loaded into RAM).

    Compiling a word in RAM memory into a target in Flash memory will now abort compilation, throwing a "target?" error.

    Due to some refactoring and optimization, the size of the STM8  eForth binaries stays the same!

  • W1209 "Lemons"

    Thomas02/17/2018 at 22:51 0 comments

    Several people received more or less compatible W1209 clones from vendors:

    • different PCB, fully compatible
    • compatible but 5k and 10k instead of 20k Rsense
    • common anode instead of common cathode 7S-LED-Display
    • same PCB but Nuvoton N76E003AT20 (8051) instead of STM8S003F3P6

    @richard helped raise the issue, and provided a Wiki entry that helps you telling clones apart. Unfortunately vendors don't always show the variant you receive.

    If you get one of the compatible clones you're lucky, and also the resistor variants are easy to deal with. Fortunately Zoltan documented the common anode variants, and provided the board configuration W1209-CA.

    If you get a W1209 with a Nuvoton chip the only thing you can do is replace the µC, and call the vendor names, of course.

  • STM8 eForth: Bugfix for PICK

    Thomas02/09/2018 at 17:10 0 comments

    M. Mahlow reported what appears to be an old STM8 eForth bug:

        1 PICK equals DUP

    The correct behavior is:

        0 PICK equals DUP
        1 PICK equals OVER

    Note: the correction is a braking change!

    Fact is that in STM8 eForth PICK never worked as it should. The core uses PICK only once (in .S), and there 1+ was applied just before calling PICK (with a different indentation). Of course, PICK could have been fixed instead of "fixing" a routine using it.

    In STM8 eForth 3 library functions had to be fixed ( @inter, 2OVER, and DSQRT). Hopefully not too much user code depends on the buggy PICK behavior.


    Thomas01/14/2018 at 22:02 0 comments

    I gave up on STM8L101 devices for the time being. According to [RM0013 Reference manual STM8L001xx and STM8L101xx microcontroller families, table 6, footnote 3]( STM8L10x devices must be reset after a Flash unlock/lock activity:

    The Flash program memory is write protected (locked) until the correct MASS key is written in the FLASH_PUKR. It is possible to lock the memory again by resetting the PUL bit in the FLASH_IAPSR register. Unlocking can only be done once between two resets.

    Fact is that STM8FLASH doesn't work with STM8L101 devices (e.g. STM8L001). I did quite some research, and traced the interactions between the ST-LINK V2 dongle and STM8FLASH. I also filed an STM8FLASH issue on GitHub, but I didn't get any response from the author or the community. I even checked the flash IAP routines in ST's STM8L library (there aren't any). The STM8L05x family enjoys much better support!

  • STM8L001J3: A new SOP8 chip, and the limits of STM8FLASH

    Thomas01/14/2018 at 11:17 0 comments

    The new STM8L001J3 sample, and no luck with STM8FLASH

    Yesterday I received a sample of the STM8L001J3, a package variant of the STM8L101F3 with STM8L core, 8KiB Flash, and 1.5KiB RAM. I quickly extended STM8 eForth to cover also that STM8 sub-family (the configuration is still largely based on STM8L051F3).

    Unfortunately, when I tried to flash it with vdudouyt/stm8flash I had no success. Flashing that device turned out to be impossible. Accessing the option bytes worked. Then tried to use the latest version of stm8flash (which didn't compile - I used the binary in the repository) the result was the same (in fact, the device ID had already been added to the tool, and I didn't even have to recur to using the STM8L101x3 configuration).

    I started to dig deeper: stm8flash doesn't cluster technical information about STM8 variants into family and density. It simply uses the marketing name, and leaves QA to the user. That's not the way I would do it. 

    Gathering Information about the Silicon

    ST provides a tool STM8CubeMX. It's essential features serve the use cases of interactively exploring configuration constraints of various STM8 devices based on packaging (including shared pins for a group of GPIOs, e.g. STM8S001J3, STM8L001J3, and STM8L050J3). Data about the variants is stored in xml files in the folder db/mcu. Each file contains an element <Die> which gives insight into the produced silicon for each marketed variant.

    The following script was used to get initial insight:

    gawk '/<Die>/ { split($1,a,/[<>]/); die=a[3]; split(FILENAME,b,"."); device=b[1]; variants[die]=variants[die] "," device } END {for (d in variants) {print d, variants[d]}}' *xml|sort|gawk 'BEGIN {print "Die|Devices"; print "-|-"} {p=$1 "|"; split($2,variants,","); for (v in variants) {p= p variants[v] ", "}; print p}'

    This results in the output below, which aligns nicely with what I already know about STM8 variants into family and density. I'll now check whether it's feasible to improve STM8FLASH. I also ordered some STM8L101F3 chips, just in case success with programming the STM8L001J3 depends on using the NRST pin.

    STM8L151C2Tx, STM8L151C3Tx, STM8L151F2Px, STM8L151F2Ux, STM8L151F3Px, STM8L151F3Ux, STM8L151G2Ux, STM8L151G3Ux, STM8L151K2Ux, STM8L151K3Ux, , STM8L050J3Mx, STM8L051F3Px,

    STM8L101F2Px, STM8L101F2UxA, STM8L101F2Ux, STM8L101F3Px, STM8L101F3UxA, STM8L101F3Ux, STM8L101G2UxA, STM8L101G2Ux, STM8L101G3UxA, STM8L101G3Ux, STM8L101K3Tx, , STM8L101K3Ux, STM8L001J3Mx, STM8L101F1UxA,

    STM8L152C6Tx, STM8L151C4Ux, STM8L152C6Ux, STM8L151C6Tx, STM8L152K4Tx, STM8L151C6Ux, STM8L151G4Ux, STM8L151G4Yx, STM8L151G6Ux, STM8L151G6Yx, STM8L152K4Ux, STM8L151K4Tx, STM8L152K6Tx, STM8L151K4Ux, STM8L152K6Ux, STM8L151K6Tx, STM8L151K6Ux, , STM8L152C4Tx, STM8L052C6Tx, STM8L152C4Ux, STM8L151C4Tx,

    STM8S208C8Tx, STM8S207C8Tx, STM8S208CBTx, STM8S207CBTx, STM8S208MBTx, STM8S207K6Tx, STM8S207K8Tx, STM8S207M8Tx, STM8S207MBTx, STM8S207R6Tx, STM8S208R6Tx, STM8S207R8Tx, STM8S208R8Tx, STM8S207RBTx, STM8S208RBTx, STM8S207S6Tx, STM8S208S6Tx, STM8S207S8Tx, , STM8S208S8Tx, STM8S207SBTx, STM8S007C8Tx, STM8S208SBTx, STM8S208C6Tx, STM8S207C6Tx,

    STM8S105C4Tx, STM8S105C6Tx, STM8S105K4Bx, STM8S105K4Tx, STM8S105K4Ux, STM8S105K6Bx, STM8S105K6Tx, STM8S105K6Ux, STM8S105S4Tx, STM8S105S6Tx, , STM8S005C6Tx, STM8S005K6Tx,

    STM8S903F3Ux, STM8S003F3Ux, STM8S903K3Bx, STM8S003K3Tx, STM8S903K3Tx, STM8S103F2Mx, STM8S103F2Px, STM8S103F2Ux, STM8S103F3Mx, STM8S103F3Px, STM8S903K3Ux, STM8S103F3Ux, STM8S103K3Bx, STM8S103K3Tx, STM8S103K3Ux, , STM8S903F3Mx, STM8S001J3Mx, STM8S903F3Px, STM8S003F3Px,

    STM8L151C8Ux, STM8L151M8Tx, STM8L151R6Tx, STM8L151R8Tx, STM8L152C8Tx, STM8L152C8Ux, STM8L152K8Yx, STM8L152M8Tx, STM8L152R6Tx, STM8L152R8Tx, STM8L162M8Tx, , STM8L162R8Tx, STM8L052R8Tx, STM8L151C8Tx,

    STM8AF62A8Tx, STM8AF5286Ux, STM8AF62A9Tx, STM8AF5288Tx, STM8AF62AATx, STM8AF5289Tx, STM8AF528ATx, STM8AF52A6Ux, STM8AF52A8Tx, STM8AF52A9Tx,...

    Read more »

  • New STM8 eForth v2.2.21 Pre-Release

    Thomas01/13/2018 at 06:14 0 comments

    The release notes for the upcoming STM8 eForth 2.2.21 describes some goodies. Check it out!

  • Initial Support for STM8L051F3

    Thomas12/29/2017 at 21:18 0 comments

    I had ordered a couple of STM8L051F3P6 chips months ago, and soldered one of them to a breakout-board. I had thought that getting them to work with STM8 eForth would be a matter of minutes.

    I was wrong.

    What failed to take into account was that that the STM8L family is a complete remake of the STM8S. It comes with a new reference manual RM0031 (597 pages), and it leaves it to the user to compare it with the 462 pages of the STM8S manual. Nice job, ST!

    However, after creating new register symbol files, and after figuring out that GPIOs for peripherals have to be configured manually, I had a STM8 eForth console running. Compiling Forth code to Flash also works. The background task requires fixing (the interrupt vector of TIM2 has changed).

    The STM8L family appears to have a much richer set of peripherals (DMA, 12bit ADC, RTC), much like an STM32 chip (only with less memory, and a fraction of the CPU power). Of course, the STM32F030, which, in small quantities, costs about the same, is better in almost all parameters (except the minimum supply voltage).

    EDIT: the interrupt vector issues are now fixed, and the STM8L051F3 configuration is now ready to use.

  • STM8 eForth 2.2.20: "Maintenance and Usability"

    Thomas12/17/2017 at 18:09 0 comments

    Yesterday, after 3 pre-releases, I finally decided to released a STM8 eForth 2.2.20. The main reason was the release of the W1209 data logging thermostat, which required some minor fixes (especially one that was a workaround for a uCsim bug).

    This said, the W1209 project showed that STM8 eForth is now very usable

    With 482 SLOC (i.e. including library, without empty or comment lines) the thermostat code is a good deal more complex than my previous demo programs:

    • sensor filtering and linearization
    • a 2 level menu with editor, plausibility checks, and defaults
    • a (simple) temperature controller, and
    • a data logger for 4 controller signals with text output

    The program fits in 2840 bytes which indicates that the code is rather dense (about 6 bytes/SLOC).

    What's more, the Continuous Integration chain produces µC firmware binary files from the same Forth source code that can be written, and tested interactively. In my view, STM8 eForth is now ready for practical applications.

View all 108 project logs

  • 1
    Step 1

    Get some cheap hardware (e.g. a STM8S103F3P6 breakout board for $0.65 and a ST-Link V2 dongle for $2). download the binary release, flash it, and have fun!

    If you like it, and you want to hack board support code for your favorite STM8China gadget, you need:

  • 2
    Step 2

    a Linux SDCC tool chain installation (installation instructions for SDCC & stm8flash are in the Wiki)

  • 3
    Step 3

    Clone the project on GitHub

View all 4 instructions

Enjoy this project?



BigVulcanDeal wrote 02/03/2018 at 13:23 point

'You haven't lived until this thing has thrown a 8" pair of vise-grips at you'

It seems the controller for many of the Harbor Freight cordless tools uses an STM8 mcu of some sort.


  Are you sure? yes | no

Thomas wrote 02/03/2018 at 15:09 point

STM8S are used frequently, but I'd like to see some evidence before I buy that it's "likely a genericized or pin-and-code compatible version available on the Chinese market".
The Meloncraft, however, isn't half bad.

  Are you sure? yes | no

Eelco wrote 01/24/2018 at 22:47 point

Hi Thomas

I am having an issue with MARKER. Compilation stops when I call a word that is defined just before in the same file. If I use MARKER from version 2.2.19 it works fine. Did I miss something, once again?

  Are you sure? yes | no

Thomas wrote 01/25/2018 at 03:25 point

Hi Eelco, could you please let me know the version or git hash you're using? Also please provide a code example, e.g. in a GitHub Gist or even better, as an Issue :-)

  Are you sure? yes | no

Thomas wrote 01/25/2018 at 06:27 point

On a second thought... could it be that you ran out of RAM? The available RAM didn't change much since 2.2.19 but its usage by library words might have changed.

  Are you sure? yes | no

Eelco wrote 01/25/2018 at 08:31 point

OK, I found what I was doing wrong: I forgot to define a dummy word before calling MARKER. In version 2.2.18 ( I mentioned 2.2.19 but that should be 2.2.18, I skipped 2.2.19) this was done when you uploaded MARKER, in version 2.2.20 you must do it yourself.

My apologies.

  Are you sure? yes | no

Thomas wrote 01/26/2018 at 05:40 point

No need to apologize, I still take the blame!
MARKER needs at least one word definition in RAM to operate, and that's not obvious. I'm rarely ever confronted to that because of the "#include STARTTEMP ... TARGET ... ENDTEMP"  template I apply. In my main.fs, TARGET is usually defined as ": TARGET NVM ;"  before STARTEMP in the first module even issues "#require MARKER" ( ).
Maybe I should  re-introduce a dummy word in MARKER. 

  Are you sure? yes | no

Eelco wrote 11/18/2017 at 14:09 point

Hi Thomas

I am encountering strange behavior when allocating ram to variable arrays.

e.g.  NVM variable qqq variable zzz RAM

qqq $20 allot drop

zzz $20 allot drop

qqq $20 $AA fill

zzz $20 $BB fill

qqq $40 dump

  80  AA AA BB BB BB BB BB BB BB BB BB BB BB BB BB BB  ________________
  90  BB BB BB BB BB BB BB BB BB BB BB BB BB BB BB BB  ________________
  A0  BB BB  0  0  0  0  5 61 6C 6C 6F 74  0  0  0  0  _______allot____
  B0   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  ________________ ok

It seems the second array is using the same space as the first one.

I am trying to communicate with sdhc cards FAT32 file systems in SPI mode. Using one array for 512 byte data buffer works great but now I try to define a second array as a filename buffer and I run into this problem. Do you have a solution? Btw I tried with the latest version, 2.2.20.

  Are you sure? yes | no

Thomas wrote 11/18/2017 at 15:48 point

Hi Eelco,

there are two issues with your code:

One is related to how VARIABLE works in NVM mode: memory is allocated from a small pool (just 32 bytes) which is reserved during COLD. The implementation is described here: [ ]. Of course you can allocate more memory than there is in the pool, but then you'll have to cycle through cold before using it.

The second is a "Forth thing". You'll have to allocate memory directly after defining the variable. Of course it's possible to create a malloc()-like device, but variables are static.

The following log shows the procedure:

STM8eForth 2.2.20
here . 160 ok
nvm variable qqq $1e allot ram ok
nvm variable zzz $1e allot ram ok
STM8eForth 2.2.20
here . 224 ok
qqq $20 $aa fill ok
zzz $20 $bb fill ok
qqq $30 dump    
  80  AA AA AA AA AA AA AA AA AA AA AA AA AA AA AA AA  ________________
  90  AA AA AA AA AA AA AA AA AA AA AA AA AA AA AA AA  ________________
  A0  BB BB BB BB BB BB BB BB BB BB BB BB BB BB BB BB  ________________
  B0  BB BB BB BB BB BB BB BB BB BB BB BB BB BB BB BB  ________________ ok

I assume that you use a low density device with just 1KiB RAM. You can try using the EEPROM for storing the second buffer - writing it is slow but for manipulating the FAT it might be sufficient.

  Are you sure? yes | no

Eelco wrote 11/18/2017 at 17:05 point

OK, thank you very much, this works. I will study the link again. I am using a board with stm8s103f, 1KiB ram indeed.

  Are you sure? yes | no

Roy wrote 11/17/2017 at 14:22 point

Just hooked up a MINDEV STM8S103 directly to an HC12 wireless serial communication module at 9600 baud and have 100% console eForth results over many hundreds of metres.

HC12      STM8S

TXD        RX  PD6

RXD        TX  PD5

  Are you sure? yes | no

Thomas wrote 11/17/2017 at 20:02 point

The HC12 is quite good! I experimented with running Forth on the STM8S003F3P6 that powers the HC12. Maybe I'll continue with it at the end of the year.

  Are you sure? yes | no

Roy wrote 11/12/2017 at 12:02 point

\ C0135 display data 4 bits and power relays with LED for HI nibble

\ 12 NOV 2017 RS
VARIABLE Startaddr

$1000 Var ! \ inner delay
$40 Varloop ! \ outer delay
$8090 Finaddr !
$8080 Startaddr !

: vardelay Varloop @ 0 DO Var @ 0 DO LOOP LOOP ;
: newflasher2
 Finaddr @
 Startaddr @ DUP addr !
  Addr @ DUP . C@ DUP . Byte ! CR
  Byte @ $F0 AND $10 / \ mask and rotate hi nibble
  $10 OR OUT! \ also turn on LED
  Byte @ $F AND OUT!
  Addr @ 1 + Addr !


8080 0
8081 0
8082 5A
8083 26
8084 F7
8085 CC
8086 80
8087 68
8088 CC
8089 80
808A EC
808B 5A
808C 5A
808D 1F
808E 3
808F 51

  Are you sure? yes | no

Thomas wrote 11/12/2017 at 18:31 point

Got one? A nice little board, isn't it?
Also have a look at this one:
I don't know why they call it "5 way relay time control panel" when it has 6 relays, but I ordered one yesterday. The 11.11 price was just $10.35 (€8.87, ₤7.85).

  Are you sure? yes | no

Eelco wrote 10/28/2017 at 14:19 point

Hi Thomas 

I am trying to use a timer interrupt similar to your description ( .

I think I had to rewrite IVEC!:    (: IVEC! 2* 2* $8008 +  ULOCK ! LOCKF ; )  to be able to write to the interrupt vector address. 

: timer_4_interrupt SAVEC 0 $5344 0 b! OUT! IRET ;    \ Simple interrupt routine.

' timer_4_interrupt 23 IVEC!    \ Link interrupt routine to IRQ23 (TIM4 update).

But as soon as an interrupt occurs the chip reboots. How should I proceed to use timer interrupts?

  Are you sure? yes | no

Thomas wrote 10/28/2017 at 18:31 point

Hi Eelco,

what a coincidence! I continued working on the interrupt features, and I also got reboots. I'm currently debugging, and as soon as I've figured out what goes wrong I'll let you know!


  Are you sure? yes | no

Thomas wrote 10/28/2017 at 19:53 point

OK, that was easy but I've got no idea why it ever worked. 

Here is the fix (a new pre-release will be out soonish):

;       SAVEC ( -- )
;       Minimal context switch for low level interrupt code
;       This should be the first word called in the interrupt handler

        POPW    Y
        LDW     X,YTEMP
        PUSHW   X
        LDW     X,#(ISPP)       ; init data stack for interrupt ISPP
        JP      (Y)

;       IRET ( -- )
;       Restore context and return from low level interrupt code
;       This should be the last word called in the interrupt handler

        POPW    X               ; discard CALL return address
        POPW    X
        LDW     YTEMP,X         ; restore context

Edit: the bug was even worse than I thought - the above code does the job.

By the way: you don't need ULOCKF / LOCKF if you set the interrupt vector in NVM mode. I'll also put the interrupt vector addresses into the STM8S103.efr file so that setting an interrupt works with a simple ! (store), and IVEC! is no longer needed.

  Are you sure? yes | no

Eelco wrote 10/29/2017 at 09:59 point

Hi Thomas

Wow, that was really fast. I should have asked you a week ago, would have saved me a lot of time.

I tried setting the interrupt vector in nvm mode but with 2.2.17 this forced the chip in a strange loop, even after a power cycle. I then had to reflash the mindev board. (I think I really need to get into assembly). 

Thank you very much for solving this issue.


  Are you sure? yes | no

Thomas wrote 10/29/2017 at 20:22 point

The bug clearly was on the silly side. Next time please drop me note when it looks like you're stuck :-)

  Are you sure? yes | no

Thomas wrote 10/28/2017 at 21:11 point

I updated the example code:

I used a headerless interrupt handler but with the patch above your code should now work as intended :-)

  Are you sure? yes | no

Thomas wrote 10/28/2017 at 22:08 point

  Are you sure? yes | no

Roy wrote 10/06/2017 at 09:31 point

Microchip produced a humorous self-critical video about the failings of the PICkit 3 vs the older 2. Perhaps ST Micro should be shamed to do the same with their products. I realise that this is off topic but still a good example of how not to do things and take ownership for getting it wrong. My ST Visual Programmer is 3.4.0 Jul 12 2017.

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Roy wrote 10/04/2017 at 17:23 point

Having lived in Quebec a long time ago, there is a local swear word that sounds like ST. This is what I say every time I use ST software and hardware. STVP does not even show the latest factory ST-LINK/V2 as an option - 'ST-LINK All Versions' would be useful. The thing never connected as I tried a few times a year over many years. They do nothing to alert you that the target device needs external power. I always had clones that did the job so there was no great urgency to learn it.

Many (all?) of the cheaper USB - STM programming adaptors had figured this out a very long time ago. Even Microchip PICkit 2/3 monitors power on the target but gives the option to power their external devices.

Simply logging in to ST to get free software goes into an email / validation death spiral loop that is a complete waste of our valuable time. If the people of ST responsible for this nonsense worked for me, then they would be all unemployed.  


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Eelco wrote 09/30/2017 at 16:11 point

Hi Thomas

I saw you solved the issue. Great! Thanks.

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Eelco wrote 09/27/2017 at 18:13 point

Hi Thomas, I am enjoying your project for more then a year now. Today I joined hackaday to be able to participate. I bought a couple of W1209 and mindev boards to play with. I also have an ssd1306 i2c oled display (about $3 at Aliexpress). I managed to drive it using the i2c capabilities of the chip, no bit-banging. This was a few months ago, with version stm8ef-bin.2.2.8 and a MINDEV board. I used $" to compile the text to be send to the display (e.g. : txt $" text" ;) I upgraded to more recent versions, up to 2.2.16, but executing a word that contains $" freezes (or reinitilizes, as with COLD) the board. What am I doing wrong here? Do I have to raise a flag in Can you point me in the right direction?

Btw, I'm happy to share the code if anyone is interested.

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Thomas wrote 09/28/2017 at 06:07 point

Hoi Eelco,

thanks for letting us know about your work! Your contribution in the I2C field would be very much appreciated!

Also thanks for reporting the issue with $": this is a regression. It's tracked here, and I'll fix it as soon as possible.

The root cause is insufficient testing. Some of the progress for building a test infrastructure is tracked here:

I would love to have you in the team at GitHub. I'm quite sure that the other team members would say the same.

Met friendelijke groeten,

  Are you sure? yes | no

Eelco wrote 09/28/2017 at 08:43 point

Hallo Thomas

Thank you for your kind reply and invitation, I would like to join. I have to warn you though that I have little coding experience but I am learning thanks to projects like yours. How do I proceed to upload the code?

I just saw you have a separate project with W1209 thermostat boards. I use two of such devices in my household: one as a replacement thermostat in a refrigarator. The other one in the boiler of the central heating unit. Maybe I can make small contributions on that project too.

mit freundlichen Grüßen


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Thomas wrote 09/30/2017 at 12:20 point

Hi Eelco,

the only way to gain coding experience is coding. There is still a lot you can do, e.g. write tests (which improves coding skills significantly!), or write library code (e.g. I2C), or do a review (also a great way to learn), or spread the word... Please let us know your GitHub ID, and you'll receive an invite!

A warning about W1209 in safety critical applications:
* only use hobby stuff for adding features that aren't safety critical
* always rely on built-in safety features of the product
* make sure to get a review of your design from someone who knows safety

Creating a HaD-project is a great way to get feedback from experts!

  Are you sure? yes | no

richard wrote 10/05/2017 at 03:08 point

Hi Eelco,

I would welcome seeing your code. I'm likely to use i2c one day and your code will give me a head start.



  Are you sure? yes | no

Eelco wrote 10/05/2017 at 08:47 point

Hi Richard

Here is the link:

Please let me know if  you have recommendations for improvement.



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richard wrote 10/05/2017 at 15:04 point

Hi Eelco,

thanks for the code below. Already I have learned about the B! word from reviewing your code. That's going to help me enormously with my W1209 project where I want to turn an input port into an output port for some of the time.

You've done a much better job than I would have. Thanks again


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Eelco wrote 10/05/2017 at 21:59 point

Hi Richard

You're welcome, I am glad it is of use to you. I uploaded another file on my github account with io-manipulating words: io.fs. These words use a numbering of the gpio-portpins. The word io. displays the state of the IDR,ODR,DDR,CR1 and CR2 for a portpin. (e.g. $15 io.  displays these bit states for the  second port (Port B), pin 5. Maybe useful for you as well.

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Peter wrote 08/21/2017 at 14:11 point

I'm a newbie and have implemented eForth on a STM8S103F3. While I have successfully implemented the "mystart" boot example which remains in NVM  following a power reset, I just can't seem to get any other created word to be available. Could I have some guidance please? 

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Thomas wrote 09/24/2017 at 07:24 point

Hi @Peter, sorry, I noticed your message just now, which is very unfortunate. Yesterday I independently found the problem you were facing. The problem, which existed since 5/August/2017, has been fixed. A new binary release is being prepared.

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Thomas wrote 09/24/2017 at 08:38 point

I just released v2.2.16 to fix this issue.

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Peter wrote 09/25/2017 at 20:56 point

Hi Thomas. On my second MinDev I was able to re-programme it using STVP ID 3.4.0. However as it says "stm8eForth v2.2" which is identical to other boards, how do I distinguish it elegantly via communication? Incidentally the first board which has been running a blink programme as an endless loop on "problem 2.2.13" refuses to re-programme via SWIM reporting not blank though ROP is off. Any suggestions on recovering it?

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Thomas wrote 09/29/2017 at 18:06 point

Hi Peter,
you have a point there.  @barewires already filed an issue. I'll be looking into it!

  Are you sure? yes | no

Peter wrote 10/13/2017 at 13:50 point

Hi Thomas, small update to follow. I don't know whether it's my ignorance but I was expecting to be able to reply as another indent to your reply 09/29/2017 at 18:06 but replying via 09/24/2017 at 07:24.

  Are you sure? yes | no

Peter wrote 10/13/2017 at 14:28 point

To cover my experience described earlier I'll split it into two responses in case anybody wants to work on that part of it. I have not been doing any compiling but just running STVP in windows burning IHX files as required. Any compiling I'm likely to do will be in Windows as I've found setting up a Linux similar to what I use a challenge (...ST). Zorin I'd suggest is a better start that many.

I solved how to re-programme a stubborn STM8S103F3P6 mentioned by specifically selecting the Option Byte window tab and then using Program > Current Tab.  Then I was able to program as I normally do so by using Program > All tabs.  Possibly a glitch but nothing else worked.

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Peter wrote 10/13/2017 at 17:59 point

To distinguish between the different versions of 2.2.xx appearing as v2.2 I've started to modify the IHX file so that the same 4 bytes now display 2v17 for example. I'll explain the procedure for newbies like me used to Windows.

1. Copy the IHX file and rename including the version and change the file type to HEX. e.g. C0135.IHX becomes C0135-2v17.HEX.

2. Open the file using STVP and choose the Program Memory tab to display both the hexadecimal and ascii contents.

3. Go to around line 000081E0 and you should see in the ascii columns on the right  stm8 eForth v2.2. Put the cusor on the v and update. The hexadecimal will change.

4. Save

Now on STVP default settings the files are easily accessible. For me the approach above is easier than directly locating the file with STVP and using the Save As to create the HEX copy. 

  Are you sure? yes | no

Thomas wrote 10/13/2017 at 20:25 point

Hi Peter, thanks for updating on the Windows tools!

I'm currently working on `` - it should mirror the properties of e4thcom (require, \ res, \\ Example). Maybe the same is achievable on Windows with ``.

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jeff1937 wrote 07/29/2017 at 07:38 point

Just wondering does anyone know if it could it be possible to read the temperature of a W1209 via wire serial communication ?

In other words I just want to log the temperature to a computer, but still leave the W1209 to function as a thermostat.

  Are you sure? yes | no

Thomas wrote 08/05/2017 at 13:08 point

Yes, that's possible. The steps are as follows:

1. determine the R_ntc to voltage function (e.g. using a trimmer and an unmodified W1209, 5 values, e.g. 0 deg C, 80 deg C, and 3 values around (and including) the temperature you care most about)

2. flash W1209-FD from the v2.2.13 release

3. determine the ADC6 values for relevant R_ntc from 1.

4. create an interpolation function from 3.

5. write a simple background task that does thermostat control by reading ADC6 and using 4.

6. read the temperature value from 5. using console commands from your computer. Alternatively send the values in the background task

If you describe your use case more precisely, I can write something to get you started

  Are you sure? yes | no

jeff1937 wrote 08/06/2017 at 00:47 point

Thanks Thomas for the helpful reply.

My applications are to turn off a immersion heating element in a cooking pot when the water reaches near to boiling and secondly to operate a fan in a solar dryer at a temperature around 100C, with computer logging every 10 minutes or so.

Thanks for your kind offer of assistance, but I will try to get some unmodified W1209s operating in a circuit, just to get started first.

If I was able to reflash them, I would hope to retain the 3 digit temperature display.  Which sounds easy as you say they are fully supported by STM8EF vectored I/O.

I guess the key pins don't operate when they are used for serial connection, which is OK because the temperature points could be hard coded in software.

  Are you sure? yes | no

Thomas wrote 08/06/2017 at 05:07 point

Jeff1937, thanks for the info! How do you think about making a small project out of this? I've got a feeling that quite some people would be interested in using this :-)

Know what, I've got a couple of spare W1209 boards here. I'll start a new project, and invite you as a team member. Does this sound good?

  Are you sure? yes | no

jeff1937 wrote 08/06/2017 at 06:54 point

Also was thinking that you could use a datasheet for an NTC 10K.

It shows a resistance table between -55 to 125°C.

eg 25°C = 10,000Ω, 80°C = 1,068Ω,  100°C = 549Ω

Then calculate the theoretical voltage at PD6 with a 20k pull-up to 5V.

This would need a later calibration correction adjustment, but should give a good starting point.

  Are you sure? yes | no

jeff1937 wrote 08/06/2017 at 06:59 point

Yes I would like to have a go at making this a project, or helping.

My W1209 boards haven't arrived yet, but there's plenty to learn in the meantime.

  Are you sure? yes | no

Thomas wrote 08/06/2017 at 07:02 point

Good idea, at least to validate the temperature readings we get.

By the way, I started a HaD project for this. Let's continue with our discussion there!

  Are you sure? yes | no

Thomas wrote 08/06/2017 at 07:16 point

Ok, great! Get's let started. Please visit the project page, and "Follow" the project to get a notification when there is something new.

There is a first project log, where you can add comments. I also added a GitHub project for code and docs.

See you there!

  Are you sure? yes | no

jeff1937 wrote 08/06/2017 at 08:02 point

OK, will follow you there, thanks Thomas

  Are you sure? yes | no

richard wrote 07/22/2017 at 02:02 point

My first attempt at using a W1209 board has been very rewarding. A couple of suggestions for anyone starting out and for the project team:


1. I had no success flashing the board with the suggested ST software on  You may also consider the ST software used by the person who published the schematic of the W1209. It can be found at


2. When putting the header on for the SWIM connector use 5 pins instead of 4. The 5th pin is a convenient place to tie one end of the diode to for the half duplex link.


3. While the SWIMCOM binary may work on the W1209 board, for the newcomer there is a lot of reward in seeing the "4th" string on the LED display once the binary is flashed. With that feedback you know it is just a matter of getting the serial comms to work.


4. With the extra pin the SWIM connection would be a much better place to have half duplex communications. It would prevent the serial communication from disrupting measurements on the sensor pin while debugging and gives you a pin that your push on connector holds better.


5. Is there a place to share code snippets? For instance, I wanted to blank the display before sending another character to it. I used

 : Clrdisplay \ clear anything showing

        32 E7S 32 E7S 32 E7S ;


I also wanted a delay between displaying “On” and “Off”. I used the following but I suspect there is an easier way:


variable bigtimer


: tSet TIM 1000 + timer ! ;

: tTest TIM timer @ - 0 < ;

: delayInner tSet begin ttest until ;

: delay 0 bigtimer ! begin delayInner 1 bigtimer +! 25000 bigtimer @ - 0 < until ;


If there was a way to share these snippets it may prove useful to the newcomer. Maybe I just don’t understand the features of github well enough *grin*.


Anyway, I can recommend this forth implementation to anyone looking to hack one of these boards. I’m having a blast . I only wish I had found about this project before I built my electric gate controller with an atmel avr chip programmed in assembly. I could have just brought a cheap relay board and achieved the same thing without having to fabricate a board, populate it then program it in assembly.


Keep up the great work team.


Kind regards


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Thomas wrote 07/22/2017 at 08:49 point

Hello Richard, thanks for your comment, it's higly appreciated!
Here are a few pointers to related actions, some new, some in the making.

1: the Wiki is updated

2, 3, 4: using a 5-pin header and a diode is a good idea! I'm currently experimenting with using the W1209 key GPIOs (PC4, PC5) for full-duplex communication, which has several advantages. What do you think?

The usability of STM8EF programming is currently under active development.   Especially a. and b. should be helpful for new users:

  a. improved full-duplex serial code, e.g. for W1209
  b. e4thcom support with libraries
  c. temporay "scaffolding" code in RAM
  d. board hex file generation in uCsim

5: I created a GitHub Gist with your code snippets - let's see if that works as advertised: 

I created an issue on GitHub
It would be great if you could contribute to  taking the decisions for a better W1209 support. Also feel free to open an issue on GitHub for topic oriented discussion.

Thanks again for your contribution.

  Are you sure? yes | no

richard wrote 07/22/2017 at 10:04 point


great stuff. I've been at it all day so real life drags me away for now. I don't have much to contribute on full or half duplex serial. I used Teraterm and slowed it down (25ms each character, 500ms for each line return) so the compiling could keep up. I was happy with that.

The Github Gist is interesting. Over time it could be really useful. Perhaps the main Github wiki needs to alert readers to it's existence?

I'm happy to help out with the W1209 where I can. You've no doubt heard of the saying "the blind leading the blind". 

The W1209 is a great platform and it is very exciting to think that much of what I used F-PC for years ago I could do on something costing so little. I plan to contribute as much as I can. 



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Thomas wrote 07/22/2017 at 12:59 point


the voice of users is important, especially in a hobby project where there is no such thing as "market research" - users know very well what makes a product  useful for them. One I'd like to figure out is if connecting a serial interface to the keys "+" and "-" is acceptable (the keys will remain usable), at last during interactive programming. The other thing is whether support for "sensor header COM" needs to be maintained, or if I can simply replace it with something better :-)

  Are you sure? yes | no

Thomas wrote 07/22/2017 at 17:06 point

FYI: issue #41 is closed (which means that full duplex communication now works without character delays). I'll make a pre-release.

EDIT: please check the project log

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RigTig wrote 02/27/2017 at 21:59 point

Thomas mentioned that a better file loader would be nice. Here is my attempt. Simple to start with, but obviously capable of being expanded with features later. It is in Python2 and runs from the command line of the host machine (mine is LinuxMint).


#!/usr/bin/env python2

import serial
import sys
import time

port = serial.Serial(

if len(sys.argv) < 2:
    print('Usage %s ... [fileN]' % (sys.argv[0]))

def upload(path):
    with open(path) as source:
        for line in source.readlines():
            line = line.strip()
            if not line: continue
            if len(line) > 64:
                raise 'Line is too long: %s' % (line)
            print('\n\rsending: ' + line)
            chin = ''
            response_buffer = []
            while chin <> '\v':
                while port.inWaiting() > 0:
                    chin =
            response = ''.join(response_buffer)

for path in sys.argv[1:]:
    print('Uploading %s' % path)


Usage: Save this code as a file (say named and change its permissions to be executable (just the lines in between the code tags). I put in my local /bin folder. Edit so the port matches what you use when using a terminal console to connect to STM8 machine.

WARNING: I've just noticed that the indentation was inconsistently displayed, and python is indentation sensitive. So be very careful with just copy-and-paste. I'll put a copy of it up on RigTig's Big 3d Printer project here on

Either put FILE on first line of the file to be sent, or type it into a terminal console and close it, then use a local command line interface thus: <code>  filename file2send </code>. Enjoy!

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Thomas wrote 02/27/2017 at 22:26 point

Hi RigTig, this is cool! Now the last reason not to learn Python (the haploid language, as I use to say) has gone. I'm going to need it in my job, anyway ;-)

PS: I just added the tag v2.2.8.1.snapshot, and this means that the binary size of CORE is below 4096 bytes, complete with the new "transparent" VARIABLE feature

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Thomas wrote 03/04/2017 at 11:07 point

I just tried your script - the handshake seems to work, and compiling code to NVM is very fast compared to the "worst case delay" method!

However, I had to interrupt the script with ctrl-c after the transfer was finished. The reason was that my Forth code ended with "HAND", after which waited in vain for the handshake signal.

I can imagine that an improved uploader does the following:

* handle FILE and HAND (no need to include those in source file), or

* terminate transfer when the response is anything but the handshake character

The next thing on a programmer's wish list is a way for including source files (nested, of course). I can also imagine testing if "base code" has already been transferred, e.g. using some query-response between the Forth system and the uploader.

  Are you sure? yes | no

Thomas wrote 02/27/2017 at 22:26 point

Hi RigTig, this is cool! Now the last reason not to learn Python (the haploid language, as I use to say) has gone. I'm going to need it in my job, anyway ;-)

PS: I just added the tag v2.2.8.1.snapshot, and this means that the binary size of CORE is below 4096 bytes, complete with the new "transparent" VARIABLE feature

  Are you sure? yes | no

RigTig wrote 02/23/2017 at 05:44 point

Thanks Thomas for a great environment in which to have lots of fun. I needed VARIABLE to be defined in NVM, but to keep its data in RAM. Some variables need to change for every data line processed (megabytes of GCODE), so using NVM is just not going to cut it for real use. Besides NVM access is slow. So, here is my replacement definition for my project:

: variable create here , 2 $6e +! does> @ ;

Now, this works only in NVM mode, because it makes no sense to use it in RAM mode anyway. Besides the DOES> part would be wiped every COLD or restart. The magic address of $006E is the address of next available RAM when in NVM mode.

If you want to test after a restart or COLD, you need to adjust the address of next available RAM to be after the last used address by a variable. In my case, the last used address was $009e. Note that in RAM  mode, the address of next available RAM is at $006A. So, I typed

$a0 $6a !

and then initialised all variables and they just work. Now this hack is not for every project (obviously), but does show what can be done when a need arises. Enjoy!

  Are you sure? yes | no

Thomas wrote 02/23/2017 at 21:35 point

Hi RigTig! That's indeed a nice hack, and it is much along the lines of what I had planned.

I'd like to propose the following solution: 

1. some memory below the user dictionary in RAM shall be set aside by adjusting the reset value of USRCP
2. the next variable address for NVM routines shall be stored in the (new) variable USRVAR, which shall be initialized from USRCP
3. when switching from NVM to RAM the reset value of USRCP shall be set to the value of USRVAR

I'd like to check if it's possible to make VARIABLE work transparently in NVM and RAM mode. Most likely writing a different word is easier.

  Are you sure? yes | no

RigTig wrote 02/24/2017 at 04:09 point

Thanks for compliment. I haven't really tried to make VARIABLE work in both RAM and NVM, but I am sure it'd work. The key is just understanding that there is one level of indirection (address of value instead of value), so RAM variables use an extra 2 bytes over the non-indirect version. Nice to avoid wasting ram, but not really a show-stopper. Coding in assembler should be far more memory efficient than the Forth version, but it's the joy of Forth to be able to do these kinds of things at all (and optimise later when you find that it is really a good idea!).

A hard reset or even COLD needs to preserve the ram space needed by variables, but I prefer not to lock in a pre-determined limit on the number of variables. I also hate wasting valuable resources by committing them for just-in-case scenarios. 

So let's consider the use cases. Is there a need to support programming to NVM, then RAM, and back to NVM? If we say that all NVM variables need to be defined before RAM gets any code, is that reasonable? At least all the ram needed is in one block in this case. Probably a bit hard to communicate to programmers, and practically impossible to enforce.

Even if there is some code compiled into ram before or after NVM variables are created, the only thing needed is to set the ram space used for parsing commands to be above the last used ram for any variable. This happens anyway until COLD or hard reset. Maybe all that is needed is a persistent vector stored in NVM to be used instead of the $0080 for start of ram space for code and variables. Now the incentive is for the programmer not to waste space, so it becomes 'obvious' that defining all NVM variables before using ram for anything else is just better management of the limited ram. VARIABLE needs to update the persistent vector each time, based on current ram pointer. Variables defined in ram waste space after a COLD, but that might just be a price to pay (and is quite ok during interactive development, methinks). Mmm... and RESET needs to reset the vector to first available ram for code and variables back to its compilation default ($0080).

I am sure to have missed something in this ramble, but hey, that's what hacking is about isn't it? If I knew what I was doing, then it is not real hacking! And what other language allows you to play around with how the language itself works, so Go Forth.

  Are you sure? yes | no

Thomas wrote 02/24/2017 at 06:41 point

RigTig, we're on the same page :-) 

If you read me previous comment carefully you'll find that the "machine" needed for implementing is mainly coded in the difference between "the reset value of USRCP" and "USRCP" (there is one error though: point 2. should be "in the new variable USRVAR which shall be initialized from the reset value of USRCP"). 

One could argue that this means waste of RAM, but actually it's just a buffer for certain use cases. You already mentioned some uses cases, and how much they would "surprise Joe Programmer".

My model for the programming workflow is this:

1. start a session with COLD, reset, or flashing the µC

2. write some test code in RAM (i.e. do the things you'd normally do with the original STM8EF)

3. run COLD and set the stage (e.g. define helper words like here:
4. run NVM, define words, variables etc as you like

5. run RAM, make pointers to the newly defined words, and also to USRVAR persistent

6. return to 4. (write more persistent code) or to 2. (test your code, preferably automated)

Of course, the casual user may miss the finer parts of the "Stage/NVM/RAM/Test/COLD" cycle, but they will notice quickly that words defined in RAM can't be compiled-in (only interpreted) in NVM, and that code compiled in NVM is lost if they forget to run RAM.

As you pointed out, a certain coding style, like defining variables first, isn't difficult to get used to. Setting aside a small buffer (e.g. 32 bytes) as a variable space wouldn't be a big deal, and it would enable the "setting the stage" use case without the risk of immediately overwriting words like IVEC. It's of course also possible to cycle through the steps 2..6 more often (also as a part of the source code) , but a buffer would add some flexibility. In the extreme case (use many variables, use a huge stack), writing test code in RAM would suffer. But hey, when testing words one tests the units, not the whole program where the stack reaches its maximum size.

  Are you sure? yes | no

Thomas wrote 02/26/2017 at 09:35 point


Please have a look at this:

The new code has the features discussed above. The behavior of VARIABLE and ALLOT is transparent in NVM mode, and in most cases there is no need to manage RAM allocation. Only if one allocates more than 32 byte RAM in a session it's necessary to cycle through COLD before using variables newly defined in NVM mode.

Edit: preliminary documentation of the new feature is here:

  Are you sure? yes | no

RigTig wrote 02/27/2017 at 01:08 point

Thomas, I have to say that your approach is just brilliant. I love the idea of being able to just get more variable space if needed, and not wasting any ram either. 

P.S. We might be both on the same page, but I'm only partway down. I am still getting my head around the STM8EF code. I keep going back and changing the options for a new flash image and it is installed in a second or two. What fun to play with!

  Are you sure? yes | no

Thomas wrote 02/27/2017 at 07:17 point

@RigTig: thanks for your support! I just pushed a "size reduced" revision to the variable branch. Since I had to do some shuffling, some "review" and "testing" by "an independent person" would be great (in a hobby project that's what's known as "playing with the code" :-)

Currently some RAM gets wasted, but that could be bettered by giving the programmer control over the headroom for RAM allocation (which would be easy).

By the way, I ordered two of the radio modules you've been working on.

  Are you sure? yes | no

Elliot Williams wrote 01/23/2017 at 08:55 point

Hiya Thomas,

Got an ESP-14-powered device up and running and installed in our basement.  Long story, must write up.

Have you played around with power saving modes on the STM8?  I'm trying to get the part into the AWU / active-halt mode.  

For one, I need the assembler's HALT command, which I've been doing in the worst brute-force means possible: HERE $8e81 , EXECUTE.  (That's HALT and RET in machine code.)  

It halts, at least.  :)  

Coming back out of halt is messy -- it looks like the clocks aren't returned to their original states and so on. I'm probably going to need to implement some start-up code.  Heck, for my purposes, hooking into COLD for a complete reset will work too... That's what I'll try next.

Just wondering if you've worked on any of the low-power modes.  Either WFI (wait-for-interrupt) or the active-halt/AWU look tasty.

  Are you sure? yes | no

Thomas wrote 01/23/2017 at 19:14 point

That's great :-)

The power saving modes (like the watchdog) still are on my "important things that I plan to do" list. You know, that's the list on the sheet after "new and exciting things I want to play with", which in turn comes after "bugs I must fix now".

Let's put it on the "important new features for pilot applications" list :-) 

What we need is:

* a word HALT that contains the HALT instructionknow

* a word SLEEP, that stops unnecessary interrupts (user defined, and application specific). This word should run HALT. When the execution continues right after HALT, SLEEP shall re-enable "waking" interrupts

* if required a word to restore clock settings (RM0016 mentions something in 10.2.2 and in 9.9.4 "Clock master switch register (CLK_SWR)", but right now I don't undertsand why the clock changes)

Do you plan to trigger a wake-up through console events? The simulated COM port should support this use case!

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Thomas wrote 01/23/2017 at 19:45 point

I added the HALT word, and it works better than expected. Here is a demo with a blinky:

    : g tim 40 and 0= out! ; ok
    ' g bg ! ok
The when I press enter after HALT the LED stops flashing. The "ok" after HALT appears after I press enter a second time.

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Elliot Williams wrote 01/24/2017 at 11:52 point


re: clocks: I read something somewhere sometime about them needing a reset.  I can't find that anymore.  I may be crazy.  

I saw some other STM8 code ( that runs the AWU without re-clocking, strongly suggesting that I'm crazy.

That code, though, makes it look like (if interrupts are enabled) the AWU reset lands in the AWU ISR, which is uninitialized ($0000) in the vector table at $800C.

I just ran your BG example above, and it halts, but never returns until hit with a hard reset. I wonder if your code is working b/c it NOPs off to the next ISR and you got lucky.  Or does it actually try to execute whatever's at $0000?

So: how do we set up ISRs in eForth?  (Or, how do you write bytes directly to flash?)

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Thomas wrote 01/24/2017 at 19:23 point

TL;DR: the quick-fix: an AWU "driver" that does it all but I would prefer a Forth solution and this requires some design decisions.

Long version:

Due to limitations in the SDCC tool chain any interrupt must be declared in main.c. Writing ISR vectors to Flash might work, but it requires a good approach for registering (and unregistering) interrupts to be viable (I'm thinking of RESET). Also Forth VM context switching would have to be done before executing any Forth code.

Another approach would be a "catchall" interrupt handler for several interrupts that then redirects to Forth code. This has the advantage that the context switch can be handled in a uniform way, but the dispatching won't be very efficient (or again a lookup).

This brings us to the next problem: some interrupt sources require resetting some bit in some peripherals control register. Leaving that to user code is very error prone, and a "catchall" interrupt handler would have to do it for all possible sources or leave it to user code.

What do you feel about of a middle way?
* Interrupt handler declared in main.c
* basic handler code in assembler or c to do a context switch, and to clear the trigger source
* handler code in Forth registered through something like BG

A last point: how many concurrent "Forth code interrupts" can we allow?
* Level0 we have the console
* on Level1 is the BG interrupt
* on Level2 is TIM4 (for COM simulation)

I guess that some stuff like TIM4 shouldn't have to compete with other code (the current code is efficient as it gets). Most likely it's possible to drop the interrupt level in BG code to Level0, and use Level1 for Forth handlers without character-I/O. The latency would still be in the lower µs range.

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Elliot Williams wrote 01/25/2017 at 12:43 point

How does the 'BOOT mechanism work?  If you could do placeholders for the various ISRs like that, the user could write their handler function and store its address in the right place?  That seems very Forthy to me.  <code>: awu-isr stuff ; ' awu-isr ISR_AWU ! </code> or something.  One of these functions / memory locations per IRQ and you'd be done?

On resetting the flags as you leave the ISR: I think that should be user code rather than bloating up the system with it.  Yeah, it's going to hang the system if you do it wrong.  If I could count the number of times I've pressed the reset button...

On context switching in ISRs:  I'm not sure I understand the full details.  Unlike C, there's not necessarily any context to switch?  If the ISR maintains stack balance then there's no need for any context?  Leave whatever's on the stack, and it'll still be there when the interrupt is done?

For me, personally, I'd just be stoked to have a pointer to an address that I could set to execute when the AWU IRQ fires.  The rest, I can handle in code, I hope. :)  (Assuming that the return from interrupt works right.)

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Thomas wrote 01/25/2017 at 20:20 point

'BOOT is simple: it returns the address of the "Parameter" field (like DOVAR). To safe code I used it to get the address of the whole following table of initialization values for USR variables. After switching to "NVM" it's possible to simply overwrite all these values. There is a 2nd copy to restore these values, e.g. to "forget" user vocabulary in Flash memory with RESET.

Yes, the 'BOOT method can be used in for interrupts, too, but that would require one more level of indirection.

About context switching:

my first approach was to re-use the Data Stack, but I quickly learned that X isn't always a valid Data Stack Pointer: it does that at the start and the end of a word, but not always in between ("always" is a very important attribute when writing interrupt code). Before implementing the background task, I tried  to make sure that X always represents a valid stack pointer in all primitive words. However, I failed to get it working until I started using a 2nd Data Stack for the background task (which I didn't like since it appears wasteful). Later on, I applied coding techniques that use X for reducing code size. Of course, it's possible to re-factor the code. It would be interesting to compare other multi-tasking Forth implementations. 

I went in a different direction: In several refactoring rounds I removed the following variables entirely: TEMP, XTEMP, PROD1, PROD2, PROD3, CARRY, and I also made the I/O context leaner.

Now, for code without character I/O only YTEMP must be saved. Otherwise also BASE, PAD, and HLD must be taken into consideration. And, of course, we need a stack. One approach would be to have a floating "stack pad" to work around the "X!=TOS" problem.

I guess it will take some time to implement a full featured solution for Forth interrupt handlers.

A minimal solution might look like this:
* a word IVEC! to set an interrupt vector
* a word SAVEC to save the context
* a word RESTC to restore the context, ends with IRET

The application could then define a word in the following way:  

: handler SAVEC ( some stuff ) RESTC ;

 ' handler 1 IVEC! \ set the AWU interrupt handler

Now that I'm looking at it, this doesn't look too bad.

Edit: I made some corrections, added some details, and added one more option for a solution

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Thomas wrote 01/25/2017 at 22:23 point

I added the solution above for testing to the develop branch. Due to the mentioned limitations it's currently necessary to initialize the interrupt to priority low (0:1) (it shares the data stack with the ticker).

I also changed TIM4 to prio "highest", which might allow to implement all user defined interrupts with priority "high" later on. This would then require 3 data stacks with the sizes normal (console), medium (background task) and small (interrupt handler).

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Thomas wrote 01/26/2017 at 20:48 point

@Elliot Williams:

Here is a starting point for Forth code user interrupts and AWU usage:


  : awuint savec awu_csr1 c@ drop restc ;

  ' awuint 1 ivec!

  : initawu 38 awu_apr c! 1 awu_tbr c! 16 awu_csr1 c! ;


When I run HALT with this code, it returns immediately. Since I didn't find the time to make sense of the AWU configuration, I simply took the AWU timing values from the page you mentioned before.

Please not that this currently only works when I run HALT from the console (I still need a solution for the Data Stack problem). Running HALT from the background task would change the contents of the first element on the stack (which would work if the stack were empty).

A quick fix here is to assume that X represents TOS when HALT is executed (which is the case), and skip initializing the stack. Please note that this only works for HALT, and not in the general case.

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Thomas wrote 01/23/2017 at 21:51 point

Changes are in the develpp branch on GitHub. The 2.2.6.snapshot release contains new binaries :-)

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Youlian Troyanov wrote 01/26/2017 at 04:51 point

please write your long story about esp-14 :)

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Thomas wrote 01/27/2017 at 22:19 point

Elliot, in order to get a simple and practical solution, I now propose the following:

1) In RAM code IVEC! (its only used once for setting an interrupt handler

: IVEC! ( a n - -  ) 2* 2* $800A + ! ;

2) Implement HALT as a user word:

: HALT  ( -- ) [ $8E C, ] ;

3) Implement your interrupt handler using SAVEC and RESTC (make sure not to use more than 8 cells on stack)

This will work for any interrupt. Please make sure to change the interrupt down from highest to high.

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jaromir.sukuba wrote 01/23/2017 at 05:17 point

Another tip for *possible* STM8 target

I didn't buy this one, haven't seen the schematics, but to me it totally smells like it could have STM8 under the display. Googling for XK-001T-1 didn't bring much info, though.

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Thomas wrote 01/23/2017 at 06:18 point

Yes, that's possible. In most cases one won't find any schematics, and also the XH-, XK, M- or B monikers aren't always used the same. There is a small list of modules that are very likely STM8S based in the Details Section of this project (in the section "How can I spot suitable boards?"). If there is any interest, I can publish a list with advertised properties and the "street price".
Edit: here is a link with a picture showing the PCB legend:
Based on the outline of the µC I would expect it's not STM8 but a STC15 based, a µC which I've seen several times on "timer" boards (MCS51-like

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Elliot Williams wrote 12/13/2016 at 23:13 point

Got my ESP-14 up and running last week, and then got distracted.  :)

Short story: it's just a STM8 chip and an ESP8266, like it says on the package.  The TX/RX lines are internally connected, so I was running your Forth on the STM8 with the ESP8266 powered down, and running all manner of software on the ESP with the STM8 powered down.

Been thinking about how to use both at once. 

a) Jeelink is a nice transparent serial port over ESP8266, which would provide remote wireless development of the Forth system on the STM8.  The idea of telnetting over WiFi into an STM8 is funny enough that I'm definitely going to do this.

b) Since the serial port is the only way in to the ESP8266, and the STM8 has only that one hardware serial port, I suppose that bit-banged serial or I2C/SPI could be used to talk to the console. I don't know how hard/easy this is. But then you'd have an STM8 that could issue AT WiFi commands, for instance, or run routines in NodeMCU, which might be very cool.

c) The other option is to code up the ESP and STM8 to take turns based on control characters: 0xFE toggles the ESP on/off the line, and 0xFF toggles the STM8, for instance.   This requires modifying _both_ firmwares, but would allow for the console, ESP, and STM8 to share the UART lines and talk to each other.

Just brainstorming so far. No real hacking yet. 

The breakout board I made for the module just fit it onto a breadboard, because I didn't really know what to expect from the module. It will probably want a transistor so that the STM8 can turn off the ESP8266 for power-saving when necessary, and will certainly want at least a jumper for flashing the ESP.  

Thanks for the case insensitive addition, and for do loops! This is a fun system to play around with.

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Thomas wrote 12/14/2016 at 19:31 point

Options a) and b) look good to me, especially in combination. How about connecting a PNP transistor for the ESP8266 power supply to PD1/SWIM? Normally one would access the STM8 serial port through ESP-Link, and the ICP interface could be used for direct access to the ESP8266 serial interface by simply pulling down both NRST and PD1/SWIM. Direct serial access to the STM8 could be acchieved by telling it to power the ESP8266 down (this might even work using PD1/SWIM once more, e.g. by using an RC element which can be detected testing its timing).

Option c) would also be possible, but at least one of the devices would have to be able to swap RxD and TxD, and the other devices would need a "tristate" mode on TxD. The Bus approach I took for the W1209 might also work for more than two devices.

A fourth option could be to have a Forth word that issues the initialization AT commands on the STM8, and execute it with 'BOOT.

I hope to find the time for some hardware hacking in the holiday season :-)

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Elliot Williams wrote 12/16/2016 at 21:22 point

"esp-link" not jeelink.  Tried it and had a telnet / web-console controllable STM8 running your Forth.  Took like 10 minutes.

Then I spent 3 hours trying to implement something like c) in NodeMCU.

First, I thought I'd set up two TCP connections: one for the ESP to be executed locally, and one to pass through to the STM8.  Didn't work b/c NodeMCU can only do one TCP connection, it seems.

Then I thought I'd use MQTT as the transport mechanism.  But there's some glitch there with MQTT and the UART port not working right.  I'll hack more at it before I give up, but it might be time to move on to MicroPython or ESP Basic for the interactive ESP part.

Anyway, try out the esp-link for the ESP when you get around to it.  It's kinda fun.  It _does_ however leave me wanting a more capable microchip on the remote end.  For another couple bucks, I could get a lot more flash, peripherals, and etc to tether to the ESP.

All of this playing around has helped me refine what's needed in a breakout board for this thing, though.  :)

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Thomas wrote 12/16/2016 at 22:35 point

Again great news, and I'm going to test esp-link too. Multiplexing communication through MQTT topics was the first thing that came to my mind. About a year ago I tried working with MQTT and NodeMCU, but I was disappointed with the stability of the platform (though I really liked working with Lua).
I guess that the case for ESP-14 is rather thin: as I mentioned before, it looks more like proof that the ESP8266 wasn't able to meet customer requirements than like the solution the world's been waiting for. But who cares as long as it's fun hacking.
In my opinion, a decent Forth environment on the ESP8266 would be rather attractive: C.H. Ting hacked something recently, but it was just the kernel, not a complete framework with persistent vocabulary (and maybe even with source stored in the Flash memory, and maybe even a JavaScript based IDE served from an embedded web server on the chip).

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Thomas wrote 11/28/2016 at 21:33 point

Hi Elliot, it's great to hear that someone got it running, and that the docs were good for a smooth start. Anyhow, congrats for the "STM8EF Blinky"! Did you try to do that BG style, too? 

I had a look at the CAPS issue (yes, I've been thinking about that for a while ;-) ). There are some potential clashes (e.g. PARSE/parse, NEXT,next, ABORT"/abort") but the lowercase words are the hidden "implementation part", and I don't see that their name is set in stone. I decided to name them after their assembly labels (pars, donxt, and aborq). 

New code with lowercase support is on GitHub (just set CASEINSENSITIVE = 1 in If you'd like to give it a try without building, please let me know (I can drop a binary into the files section here). If there are no issues I'll make it the default.

The ESP-14 will be one of my next targets. However, I didn't find the time to make a breakout PCBs with power supply for this module. Controlling the ESP8266 supply through the STM8S003F3 would be cool. If someone with good access to PCB prototyping could do that job I'd be more than happy to contribute some ideas about the schematics.

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Elliot Williams wrote 11/29/2016 at 15:57 point

I just got an ESP-14 in the mail from ebay today.  I'll be making a breakout for it sometime in early Dec.  (Right now, I'm churning out HaD articles like mad.)  I'll share when I do.

I still have no idea if it makes any sense to run a (powerful) ESP8266 off of a (much smaller) STM8 chip.  But I'm willing to find out.  :)

I also ordered one of those LED/relay boards. Again, just for fun, but maybe I'll do something with it.

Thanks for thinking about caps.  I'll definitely rebuild and reflash. 

No, I didn't get into the multitasking / backgrounding. I just got the thing up and running, not much more.

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Thomas wrote 11/29/2016 at 19:13 point

The ESP-14 is quite strange. I can only guess that an OEM required a solution from Espressif that meets non-functional constraints (e.g. dependability, power consumption, or periphery set) that could not be met by the ESP8266. I don't think that a lack of skilled programmers was the reason. The power consumption of the STM8S003F3 in "active halt mode" is quite low, and for a data logging sensor node a battery life of a year or more with a 100mAh battery might be feasible.

The W1209 boards are really fun, especially with a background task. When you try using STM8EF with it, please let me know if the docs for the single wire half-duplex solution are sufficient.

About the case-insensitive input: you're welcome (the option has a price tag with "23 bytes" on it :-) )

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RigTig wrote 12/15/2016 at 10:44 point

I've created an adapter for ESP14 (and ESP12) to 22-pin DIL, if you haven't done anything else yet (see new project here called 'ESP-12 and ESP-14 adapter to DIL'). My ESP14s arrived today!

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Elliot Williams wrote 11/28/2016 at 13:54 point

Hiya! Been following along, finally got a few minutes to flash stuff to one of those min-dev boards.  Great fun!  I haven't done anything useful with it yet, but I've gotten the LED blinking, naturally.

One thing that's driving me nuts is the ALL CAPS commands.  Is there an easy way to either a) lower-case them all or b) make it run case insensitively?  Or would that cause namespace clashes? It makes my shift-finger hurt. 

And that's it for now.  I have to say that your directions (combined with some of the links that you list) made it very easy to get up and running with the system.  Thanks!

I'm planning a few Forth columns for HaD, and I'm still collecting chips that have working implementations.  You've added one more to the list. 

Oh, and I've ordered an ESP-14.  We'll see how that goes.  Looks like fun. 

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