STM8S eForth (stm8ef)

This is an extended and refactored version of Dr. C.H. Ting's eForth for the STM8S Discovery that turns STM8S Value Line µCs boards into interactive Forth development environments. The SDCC toolchain is applied for building the eForth core, which makes mixing Forth, assembly, and C possible.

The binary of a basic interactive eForth system uses below 3800 bytes, including the overhead from SDCC (C startup code and interrupt table). With a rich feature feature set (Compile to Flash, Background Task) and extenions (DO-LEAVE-LOOP/+LOOP, CREATE-DOES>, native bit set) the binary size is below 5000 bytes.

Please refer to the Wiki on GitHub for more information!

Overview

Features:

configurable vocabulary subsets for binary size optimizations
Subroutine Threaded Code (STC) with native BRANCH and EXIT
compile Forth to NVM (Non Volatile Memory with Flash IAP)
autostart feature for embedded applications
preemptive background tasks with fixed cycle time (default 5ms)
- robust and fast context switch with "clean stack" approach
- allows INPUT-PROCESS-OUTPUT processing indepent from the Forth console
- allows setting process parameters through interactive console
- in background tasks ?KEY can read board keys, and boards with 7Seg-LED UI can emit to the LED display
configuration options for serial console or dual serial interface
- UART: ?RX TX!
- GPIO w/ Port D edge & Timer4 interrupts: ?RXP TXP!
- half-duplex "bus style" communication through a single Port D pin (e.g. PD1/SWIM)
board support for Chinese made STM8S based very low cost boards:
- W1209 LED display & half-duplex with SW TX
- C0135 Relay-4 Board
- STM8S103F3 "$0.70" breakout board
- configuration folders for easy application to other boards
- no UART required for interactive console
Extended vocabulary:
- CREATE-DOES> for defining defining words
- Vectored I/O: 'KEY? 'EMIT
- Loop structure words: DO LEAVE LOOP +LOOP
- STM8 ADC control: ADC! ADC@
- board keys, outputs, LEDs: BKEY KEYB? EMIT7S OUT OUT!
- EEPROM, FLASH lock/unlock: LOCK ULOCK LOCKF ULOCKF
- native bit set/reset: B! (b a u -- )
- inverted byte order 16bit register access: 2C@ 2C!
- compile to Flash memory: NVR RAM RESET
- autostart applications: 'BOOT
- ASCII file transfer: FILE HAND

Canges that required refactoring the original code:

use of the free SDCC tool chain ("ASxxxx V2.0" syntax, SDCC linker with declaration of ISR routines in main.c)
removal of hard STM8S105C6 dependencies (e.g. RAM layout, UART2)
flexible RAM layout, meaningful symbols for RAM locations
conditional code for different target boards with a subdirectory based configuration framework
bugfixes (e.g. COMPILE, DEPTH, R!)
major binary size optimization

Support for STM8S Value Line µC

The availability of low-cost boards (e.g. thermostats, power supplies, WIFI modules) makes the STM8S003F3P6 the main target.

The main differences between STM8S003F3P6 and STM8S105C6T6 (STM8S Discovery) are:

8 KiB Flash instead of 32 KiB
1 KiB RAM instead of 2 KiB
128 bytes EEPROM instead of 1 KiB (the STM8S103F3 has 640 bytes)
reduced set of GPIO and other peripherals
UART1 instead of UART2

Board support:

There is board support for some easily available "Chinese gadgets". For details, refer to STM8S-Value-Line-Gadgets in the Wiki.

CORE starting point for new boards, most extra feature words disabled
SWIMCOM communication through the SWIM interface for board exploration
MINDEV STM8S103F3 low cost "minimum development board"
W1209 W1209 (also XH-W1209) low cost thermostat with LED display and half-duplex RS232 through sensor header (9600 baud)
C0135 C0135 "Relay-4 Board" (can be used as a Nano PLC)

Binaries for the listed targets are in the Releases section.

Currently, there is no support for the STM8S Discovery, since I don't have any STM8S105C6T6 based boards for testing.

STM8S003F3 "Communication through PD1/SWIM"

This is a generic STM8EF target for exploring boards where no UART pins are broken out but where PD1 is available on a SWIM ICP header. Access to PD5/TX and PD6/RX is not required, bus-style half-duplex console communciation with a software UART simulation is used instead.

Binary size about 5800 bytes
Selected feature set:
- words for register addresses (e.g. Px_CR2 Px_CR1 Px_DDR Px_IDR Px_ODR)
- compile to Flash
- EEPROM access
- background task
- eForth extensions CREATE-DOES>, DO-LEAVE-LOOP/+LOOP
- special STM8 memory access words (bit addressing, reversed access order)
- Case insensitive vocabulary
Clock source internal 16 MHz RC oscillator HSI

For serial communication the following simple wired-or interface can be used:


STM8 device    .      .----o serial TxD "TTL"
               .      |      (e.g. "CH340 USB serial converter")
               .     ---
               .     / \  1N4148
               .     ---
ICP header     .      |
               .      *----o serial RxD "TTL
               .      |
STM8 PD1/SWIM-->>-----*----o ST-LINK SWIM
               .
NRST----------->>----------o ST-LINK NRST
               .
GND------------>>-----*----o ST-LINK GND
               .      |
................      .----o serial GND

It's advisable to have at least two boards for reverse engineering: one in original state, and one for testing new code. Please open a ticket here, or contact the STM8EF Hackaday.io project before you start working on a new board!

Warning: the original ROM contents of most boards is read-protected and can't be read, and once erased the original function can't be restored (your board will be useless unless you write your own code).

Warning: if your target board is designed to supply or control connected devices (e.g. a power supply unit) don't assume any fail-safe properties of the board (e.g. the output voltage of a power supply board might rise to the maximum without the proper software). Disconnect any connected equipment, and if possible only supply the µC with a current limiting power supply!

Warning: when working with unknown boards make sure to have at least a basic understanding of the schematics and workings of the board! The author(s) of this software can't help you reverse-engineering an unsupported board. Working knowledge of electronics engineering is assumed. Use common sense!

Run make BOARD=SWIMCOM flash for building and flashing.

STM8S003F3 Core

A plain STM8S003F3P6 eForth core as a starting point for configurations

16MHz HSI,
Reduced feature set for minimal memory footprint (less than 4KiB Flash)
Reduced vocabulary for the interactive use case (e.g. for hardware testing or as a debugging console)
Selected feature set:
- compile to Flash
- serial console with UART

More features can be selected from the list of options in globalconf.inc.

Run make BOARD=CORE flash for building and flashing.

STM8S103F3 "minimum development board"

Cheap STM8S103F3P6-based breakout board with LED on port B5 (there are plenty of vendors on EBay or AliExpress, the price starts below $0.70 incl. shipping).

Binary size below 5000 bytes
Selected feature set:
- compile to Flash
- EEPROM access
- background task
- eForth extensions CREATE-DOES>, DO-LEAVE-LOOP/+LOOP
- I/O words
- special STM8 memory access words (bit addressing, reversed access order)
- Case insensitive vocabulary
Clock source internal 16 MHz RC oscillator HSI

Run make BOARD=MINDEV flash for building and flashing.

W1209 Thermostat Module

STM8S003F3P6-based thermostat board with a 3 digit 7S-LED display, a relay, and a 10k NTC sensor. This very cheap board can be used for single input/single output control applications with a basic UI (e.g. timer, counter, dosing, monitoring).

Binary size below 5500 bytes
Selected feature set:
- Half-duplex serial interface through sensor header
- 7S-LED display and board keys (P7S E7S BKEY KEYB?)
- compile to Flash and EEPROM access
- background task
- eForth extensions CREATE-DOES>, DO-LEAVE-LOOP/+LOOP
- I/O words
- special STM8 memory access words (bit addressing, reversed access order)
- Case insensitive vocabulary
Clock source internal 16 MHz RC oscillator HSI

Run make BOARD=W1209 flash for building and flashing.

Serial console on W1209

Interactive development is possible using the sensor header as a half-duplex "bus style" serial interface with an interrupt basedUART simulation that causes very little CPU overhead (9600 baud with TIM4).

Prerequists for using eForth on a W1209 interactively:

remove the capacitor next to header (0.47µF would limit the UART to about 5 character/s)
on the terminal side, use wired-or RXD || TxD (with open drain, e.g. USB CH340 with 1N4148 in series with TxD)

Alternative solution: reconfigure to use PD1/SWIM (shared with 7S-LED segment A)

Refer to the wiki.

Relay Board-4

The board, sometimes labelled C0135 or "Relay Board-4" is a low cost PLC I/O expander with the following features:

Binary size below 5100 bytes
STM8S103F3P6 (640 bytes EEPROM)
4 relays NC/NO rated 250VAC-10A (with red monitoring LEDs) on PB4, PC3, PC4, and PC5
4 unprotected inputs (PC6, PC7, PD2, PD3, 2 usable as 3.3V analog-in),
1 LED on PD4,
1 key on PA3,
RS485 (PB5 enable - PD5 TX, PD6 RX on headers)
8MHz crystal (or 16 MHz HSI)
Selected feature set like MINDEV, additionally:
- I/O words for board keys, OUT! for relays and LED
Clock source internal 16 MHz RC oscillator HSI

Run make BOARD=C0135 flash for building and flashing.

Steps for creating a new board variant

For creating a variant, simply create a copy of the base variant's folder (e.g. CORE). By running make BOARD=<folderName> flash it can be compiled, and programmed to the target.

Disclaimer, copyright

Tl;dr: this is a hobby project! Don't use this code for anything that requires any kind of correctness, support, dependability. Different licenses may apply to the code in this GitHub repository, some of which may require you to make derived work publically available!

Please refer to LICENSE.md for details.

al177 / stm8ef