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• SIMPL as an Instruction Set

  monsonite • 4 days ago • 0 comments

  As stated earlier, SIMPL will run on a microcontroller or other processor device using an interpreter which forms the basis of a Virtual Machine, which I have chosen to call a SIMPL Machine.

  The SIMPL Machine uses printable ascii characters to create a concise, human readable language.
  
  For convenience the printable ascii are divided into 4 sub-sets:

  Numbers  0-9  A numerical string will be converted to a 16-bit integer in the range 0-65535

  Lowercase  a-z   Lowercase alpha characters are generally used to call ROM based functions for printing and control of I/O

  Uppercase A-Z  Uppercase alpha characters are generally used for user defined commands, variables and registers

  Symbols     + - * /  etc.  These 33 symbols are used to define the primitive instructions and structures for the SIMPL Machine language.
  

  It is the symbol and punctuation characters which will be used to define the Instruction Set, along the lines of the MISC machines developed by CH Ting and CH Moore.

  The SIMPL instruction set is concise because each command is a single ascii character. 
  
  It takes the form of human readable shorthand which removes the need to memorise hex codes or processor specific instruction mnemonics. Traditional assembly language frequently uses mnemonics that are 3 characters long,  ADD, SUB, AND XOR.
  
  Note: Although each instruction is represented by a single character. If however a more traditional listing were required it would be an easy programming exercise to substitute the character for a more conventional mnemonic. 
  
  SIMPL replaces these with single characters which minimises the text and vastly simplifies the overheads of parsing multi character text.

  Source code is much more compact than traditional assembly language.  It can be loaded directly into RAM - either by typing or using the Send File feature of most terminal emulator programs.
  
  SIMPL could become a lingua franca for microcontrollers or microprocessors.
  
  Provided that the SIMPL VM was coded into the target cpu, whether AVR, ARM, Z80 or 6502 etc. the same SIMPL source code will run on any of the machines.  It forms a universal assemby language and could be used to replace cpu specific mnemonics and assembly listings.
  

  Instruction Primitives.

  These are allocated to the 33 printable ascii symbols.  They provide arithmetic, logic and comparison operations as well as memory and register access, looping and program flow control. 

  Using the concept of a Minimal Instruction Set Computer  (MISC) a complete machine can be created with fewer than 32 primitive instructions. 

  There have been several historical machines that illustrate this concept - such as the PDP-8, the MSP430, Marcel van Kervinck's Gigatron TTL computer and several of the Forth cpus by Charles H. Moore. 

  The SIMPL VM is based on a stack machine with a 4 level circular stack. Most operations operate on the top 2 elements of the stack.

  Arithmetical and Logical Operations 

  +       ADD

  -        SUB

  *        MUL (Left Shift)

  /        DIV   (Right Shift)

  &       AND

  |         OR

  ^        XOR

  ~        NOT

  `         INCREMENT
  

  Memory Access

  @       FETCH

  !         STORE
  

  Stack Manipulation

  "         DUP
  

  '          DROP

  $         SWAP

  %        OVER

             SPACE - used to PUSH consecutive numbers onto the stack
  
  Conditional / Comparison 

  <         LESS

  >         GREATER

  =         EQUAL

  Input / Output

  .   ...

  Read more »

• More about the SIMPL Project

  monsonite • 5 days ago • 0 comments

  SIMPL - is the acronym for Serial Interpreted Minimal Programming Language.
  

  SIMPL is an extensible language allowing it to grow to suit the requirements of the application.
  

  In this project: 
  

  • I will explain the programming concepts and the minimalist philosophy behind SIMPL.
  • I will show how the kernel is built from a few basic routines
  • There will be example code given for implementations on Arduino and MSP430
  • I will investigate how SIMPL can be ported to custom CPUs, existing as a simulation or as a soft-core implemented on an FPGA
  • I will explore the concept of the SIMPL Machine - a CPU architecture optimised for running SIMPL as it's native instruction set.
  • I will show how the SIMPL framework can be used as the basis for several applications.

  A 2 minute Introduction to SIMPL.

  The following brief example shows how SIMPL allows you to flash a blinky LED on an Arduino or similar. The Arduino is loaded with the SIMPL kernel and connects via the serial terminal, allowing commands, shown in bold,  to be typed. 13 d            First we identify that we want to use the LED attached to digital pin 13 using the d command.  1 o              The o command allows us to send either a LOW or HIGH to the selected pin 12 - 1o turns the LED on,  0o turns it off

  1000 m      We use the m command to initiate a millisecond delay in this case 1000 mS 

  10{...........}   We  create a loop using curly braces - in this case the contents of the braces will be repeated 10 times Now we put it all together as a microscript

  13 d 10 {1o 1000m 0o 1000m}   This will flash the LED 10 times ON for 1 second and OFF for 1 second

  13d10{1o1000m0o1000m}         But the spaces were only for clarity - they can be omitted. We can edit the delay periods to create different on and off times: 13d10{1o200m0o100m}            200mS on and 100mS off Or we can alternatively use the microsecond delay command u to generate audio tones into a small speaker

  13d1000{1o500u0o500u}    This will generate 1 second of 1kHz tone But SIMPL is extensible - if we like the 1kHz beep, we can allocate a user command to it -  for example B for Beep

  We do use this using colon : and semicolon ; to define our new command

  :B13d1000{1o500u0o500u};

  Every time B is typed a tone will be generated.

  BBBB    Generate 4 seconds of tone

  Now create a higher tone and call it C

  :C13d1200{1o400u0o400u}; 

  CBCBCBCB  Generate an alternating siren sound. 

   We have created a sound effect using a few numerical parameters  and a few ascii characters as commands  d  o  m  u  {  } :  and  ;  Three conventions are used: Lowercase characters a-z are used for pre-programmed commands that are generally coded into the Flash ROM
  

  Uppercase characters A-Z are generally used for User Defined commands (microscripts) or variables that are stored in RAM

  Punctuation characters and other symbols are used for arithmetic and logical operations and program flow such as looping.

  How SIMPL Works

  A small program flashed into ROM provides the serial interface and command interpreter.

  Every ascii character read in, causes the interpreter to jump to a unique block of code which executes the command action before returning to the interpreter to read in the next character.

  This very simple interpreter has amazing flexibility and can be tailored to suit the requirements of a wide variety of applications such as CNC (plotters, 3D printers, routers, laser cutters), robotics, hardware control etc. 

  The microscripts...

  Read more »

• Implementing the SIMPL Machine.

  monsonite • 6 days ago • 0 comments

  The previous log The SIMPL Machine, looked at how the J1 Forth CPU simulation could be used as the basis of a cpu targeted to execute the SIMPL language. 
  
  Here are some notes regarding the implementation on the Teensy 4.0

  A switch-case structure will translate the SIMPL ascii character commands into 16-bit instructions to feed the J1 cpu simulated cpu.

  I took the SIMPL text interpreter framework and mapped into it the J1 instructions, focusing initially on the stack, ALU and memory operations – listed below
  

  SIMPL               Operation                J1 hex code
  
  ”                   DUP                      6081
  
  ‘                   DROP                     6183
  
  $                   SWAP                     6180
  
  %                   OVER                     6181
  
  +                   ADD                      6203
  
  &                   AND                      6303
  
  |                   OR                       6403
  
  ^                   XOR                      6503
  
  ~                   INV                      6600
  
  @                   FETCH                    6C00
  
  !                   STORE                    6123

• The SIMPL Machine

  monsonite • 6 days ago • 0 comments

  In the previous log it was identified that SIMPL would be hosted as a virtual machine running from ROM on the chosen microcontroller.
  
  In this log I explore the practicalities of creating a simulated stack machine running on a Teensy 4.0 and programmed using the Arduino IDE.

  The aim is to run SIMPL on a virtual machine with a minimum instruction set with fewer than 32 primitive instructions, in order to keep the complexity down.
  

  As SIMPL is based around a 16-bit wordsize and a 16-bit address space, it will be a better fit to a machine that has a native 16-bit architechture. For this reason, much of the early exploration of SIMPL has been done on the MSP430 range of 16-bit microcontrollers, rather than the 8-bit AVR devices.
  

  I stated in the last log that the SIMPL machine would be based on a stack architecture.
  
  Unfortunately there are very few stack machines available as almost every modern microcontroller has a register based design. A large set of registers are almost essential for the efficient implementation of a high-level language such as C.
  
  With no stack machines readily available, we need to create our own stack structures in software, either on an existing microcontroller,  as a simulation, or on a soft core design on an FPGA.
  
  This provides 3 options which I wish to explore in turn.

  1. Use an MSP430 16-bit microcontroller to implement the SIMPL machine
  2. Simulate the SIMPL machine on a high performance 600MHz ARM Cortex M7 using a $20 Teensy 4.0
  3. Implement the SIMPL machine as a soft core on an FPGA using verilog.

  Option 1  will be done using a low cost Launchpad development board. Fortunately Dr. ChenHanson Ting has written extensively about implementing his eForth system on an MSP430 so the mechanics of a stack machine have already been defined.

  Option 2 makes use of the low cost Teensy 4.0 board as a target machine. The Teensy 4 with it's 600MHz clock can readily simulate many of the early microprocessors at many times their original operating speed. 
  
  Option 3. Teensy 4 may also be used to simulate experimantal cpus with custom instruction sets. One of these is James Bowman's J1 Forth cpu which might make a suitable candidate for the SIMPL machine, as it has already been implemented and proven in verilog on a Lattice ICE 40 FPGA.
  
  As the MSP430 implementation has been covered elsewhere, and the MSP430 performance is somewhat limited by modern ARM standards, I intend to explore Options 2 and 3, with a software simulation of the J1 Forth cpu providing experience that will be directly relevant to the FPGA implementation.
  
  The J1 Forth CPU

  In 2010 James Bowman created a simple 16-bit stack machine that was targeted at executing the Forth language.  Since then it has been implemented in verilog and also as custom silicon that has found it's way into a number of graphics controller ICs by FTDI and their Singaporean silicon fabricators Bridgetek Pte.
  
  The J1 is described in this J1 2010 Euroforth Paper

  
  The J1 has a very compact instruction set, a minimal stack machine architechture  and can be described in fewer than 100 lines of C code or verilog. This makes it easy to understand and easy to implement on an FPGA using opensource tools.
  
  The J1 instruction word is 16-bits wide and the individual bit fields operate directly on the hardware without an intermediate layer of instruction decoding. 
  
  However, memorising 16-bit instructions is not easy, and an assembler or high level language is essential for program development. This is where I believe that SIMPL can be employed to advantage, as a human readable pseudo-code that allows interactive programming of the J1 - as an alternative to assembly language or Forth.
  
  

  The J1 Architecture.
  

  Having read James Bowman’s J1 Paper several times over, I managed to build up a simplified model of his instruction set and architecture.

  J1 uses 16 bit long instruction words – where each word is divided into different length fields.
  
  The following 3 images...

  Read more »

• SIMPL: A subset of Forth

  monsonite • 7 days ago • 0 comments

  As SIMPL evolved it became clear that the Txtzyme command interpreter with only 13 basic commands for exercising peripheral hardware could be developed further into a virtual machine with its own tailored instruction set. 

  From an early stage in development it was decided that the VM instructions would be single character printable ascii codes. This was done initially to make the language more human readable, and was well suited the serial terminal interface. 
  
  The extensions to Txtzyme allowed SIMPL commands to be executed from RAM, and each of these commands had an accompanying command action stored as inline code in the Flash ROM.
  
  This transition from instructions in RAM, executing blocks of code contained in ROM effectively released the microcontroller from the constraints of the Harvard architecture by using a Von Neumann virtual machine.
  
  

  SIMPL and Forth
  

  
  SIMPL has been greatly influenced by the Forth language developed by Charles H. Moore between 1958 and 1970. During the 1970s it was ported onto a wide range of minicomputers and microcomputers. It is a compact and extensible stack-based language.
  

  The stack based machine is the obvious candidate for executing the Forth language as it matches the needs of the Forth machine model.
  
  As SIMPL is a subset of Forth, it would seem sensible to make the SIMPL VM a stack based architecture.
  

  Traditionally Forth was based around a 16-bit wordsize and a 16-bit addressing range that was commonplace amongst mini computers in the 1970s.  
  

  Chuck Moore and Dr. C.H. Ting worked together in the 1990s to create a minimal instruction set computer (MISC) which could efficiently execute Forth primitive instructions. Moore and Ting identified that Forth could be effectively synthesised from 32 or fewer primitive instructions.
  Chen-Hanson Ting developed an eForth model, which was a formal specification for a Forth, implemented from a set of 32 primitives.
  

  Chuck Moore took on the hardware design challenge of MISC Forth processors, and developed a series of designs characterised by small instruction sets and minimal hardware.
  

  A full sized Forth implemantation would typically be around 6K bytes.

  SIMPL proposes the use of a stack-based virtual machine, implementing a small number of primitive instructions which allow an extensible language to be created. It is suggested that the SIMPL machine can be inplemented in about  1 to 2K bytes of Flash memory depending on the target microcontroller.

  Forth on an 8-Bit AVR
  

  A tiny Forth with 28 primitives may be implemented in about 2K bytes of AVR assembly language. This implementation is by T. Nakagawa of Japan.

  To implement Forth on an 8-bit AVR microcontroller requires an average of about 10 AVR assembly language instructions to implement each primitive.  There is also the overhead of the interpreter. This slows the execution speed down by a factor of 10 or 20. On the 20MHz AVR this corresponds to about 1 million Forth instructions per second (FIPS). 

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