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• About the Firmware

  Lauri Pirttiaho • 12/25/2022 at 18:43 • 0 comments

  Tools

  The firmware for PIC16F18326 was developed as an empty project (that is, from scratch) using MPLAB X IDE 6.05 and XC compiler 2.40. The structure of the FW is described below.

  The code

  For the code, see wd1lcd.zip
  

  Main

  The structure of the main program is typical for an event-loop structured (non RTOS) FW:

  1. initialization of all modules and HW and enabling interrupts (in some sensible order)
  2. The event loop for background handling of non-time-critical tasks.

  This FW basically just receives the commands targeted to the PCF8576C LCD controller via the I2C bus, interprets the segment states to corresponding text to the character matrix LCD module, and sends the text to it. So there is just one interrupt driven process, the I2C receiver.

  There are two other interrupt driven modules in the FW, the serial console and tick. In the production FW the tick is used only to time some functionality of the LCD handling, some delays at the start-up, and the rotation of the menu texts if more than one of them are active (which is never in normal use, but happens in the segment test in the beginning). The serial console was used in the development but is not active in the production FW. But one could use it to take the display data to PC or something. However, commands can't be sent that way. For those the versions having the USB port can be had.

  The configuration words in the main.c were made using the chip configurator in the X IDE but one can write those also from scratch by referring to the relevant headers in the tools. And of course the provided chip specific header was used. It is just so much more convenient not to need to dig the registers and bit locations from the datasheet, like in the old times. The compiler compiles the bit field accesses to single bit sets and gets, just like once done with hand-made assembly.

  The project.h

  This pattern of putting the material needed in all modules, in a small FW project, to one header, I have got to used to while working with Cypress (Infineon) PSoC Creator, but I think I have seen similar practices used even before that. Handy for small projects but may not scale well to large ones, so I don't do that always.

  This header brings in the compiler/device header xc.h and stdint.h, and then defines some project specific handy macros and types, and then includes all module headers.
  

  The Modules

  The FW consists of seven modules, each described below:

  • sys: The system services 1 ms tick and interrupt server
  • fifo: A simple lock-free FIFO to pass data between interrupt and background processes. This is used by the serial console and the I2C receiver.
  • console: A simple serial two-way FIFO-buffered character interface for test commands and logging. This was used in verifying some functionalities, tracing the I2C data stream, and of course, debugging.
  • lcd: A simple putc/puts interface for writing text to the 16x2 character matrix LCD module.
  • wd1lcdemu: An emulator for the WD1 LCD glass. Given the activation pattern of the segments of the glass, the emulator interprets what is being shown and converts them to corresponding texts that are passed to the LCD.
  • pcf8576emu: An emulator that receives the command and data bytes targeted to the PCF8576 LCD controller and interprets them to backplane/segment-group pairs activating segments of the glass, and then passes them to the LCD emulator.
  • i2c: I2C receiver that interprets the I2C writes from the main microcontroller to command and data packets to the PCF8576 emulator.

  The sys module:

  This module implements the 1 ms system tick and the interrupt server. Initialization it disables the analog functions on all pins as all functionality will be digital.
  

  It also initializes the TMR0 as divide by 8000 to generate 1 ms period TMR0 interrupt. By default this microcontroller starts with 32 MHz internal clock, which is kept as is. The core divides this by 4 as PIC16 is a 4 clocks/instruction design so the peripherals operate at the familiar Fosc/4...

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