Mecrisp-Stellaris Forth for the STM32 Cube ecosystem.

Forth is an interactive and extensible language, with built-in lexical analysis (tokenizer, parser) and interpreter/compiler, needs less than 20 KiB Flash and 4 KiB RAM, unbelievable for a self-contained (self-hosted) system.

Forth is perfect for embedded systems where some sort of user interactivity like CLI and extensibility (at runtime) are needed.

C & Forth in the 21st Century. C and Forth are both about 50 years old. The combination of the strength of this two worlds results in a powerful system that outperforms other much newer systems like Python. Good design withstands the test of time.

The goal of Mecrisp-Cube is to be a complete Forth programming environment for STM32 MCUs. There are three flavors (branches) available:

• STM32WB55 (master branch) for the STM32WB55 Nucleo Board and dongle and variants for the Firefly Dev Board (firefly), Katydid Dev Board (katydid), WB5M Discovery (WB55M), STM32WB Feather (WBfeather) and the Flipper Zero (Flipper).
• STM32F405 (F405) for Adafruit's Feather STM32F405.
• STM32H74x (H743) for STM NUCLEO-H743ZI and Arduino Portenta H7 Development Board.

May the Forth Be With You!

Instant real-time programming with Forth. The Flipper Zero is an excellent portable tool for interaction with access control systems. But the display, the buttons, LIPO (2.1 Ah), GPIO, BLE, SD-Card, RTC, etc. make Flipper Zero also an ideal tool for programming on the go.

STM32WB Series has two CPUs. An ARM Cortex M4 for the application (CPU1) and a Cortex M0+ (CPU2) for the BLE protocol stack. This Forth system runs on the CPU1. Developed with the same technology as the ultra-low power STM32L4 microcontrollers, the STM32WB MCU series provides the same digital and analog peripherals suitable for applications requiring an extended battery life and complex functionalities. If you do not need wireless connectivity, thanks to CubeMX you can easily adapt Mecrisp-Cube WB for STM32L4, and probably for STM32L5, and STM32U5.

• 63 KiB RAM dictionary
• 128 KiB Flash Forth dictionary
• 50 KiB for C code
• Serial console UART / USB CDC / BLE Terminal-IO
• Filesystem (FAT)
  • Internal Flash drive 0:, 384 KiB
  • microSD drive 1:
• Integration in STM32 Cube Ecosystem.
  • Create C code from CubeMX for internal peripherals and use it in Forth
  • Calling C Functions from Forth and vice versa
• RTOS
  • Forth as CMSIS-RTOS thread.
  • CMSIS-RTOS API to use FreeRTOS from Forth.
  • Buffered terminal I/O (5 KiB buffer for UART Rx). Interrupt driven and RTOS aware, key and emit block the calling thread.
• USB
  • USB-CDC for serial communication via USB
  • Redirect console I/O like cdc-emit, cdc-key
• BLE 5.0 GAP Peripheral Role (STM32WB)
  • DIS Device Information Service
  • HRS Heart Rate Service (heart rate depends on A0 for Nucleo and A2 for Dongle)
  • CRS Cable Replacement Server service (proprietary service from STM, similar to Classic Bluetooth SPP). Redirect console I/O like crs-emit, crs-key.
• Floating-Point Unit FPU
  • Support for the floating-point unit FPU, single precision for M4F MPUs and double precision for M7 MPUs
  • CMSIS-DSP
• vi editor
• Real Time Clock RTC
• Watchdog
• Assertion and Logging

• Control (5-button joystick, Back button, Reboot)
• LCD display 128x64 pixel
• RGB LED
• Power (LIPO charger and fuel gauge)
• Vibration Motor
• Buzzer/Speaker
• GPIO (Input and Output, PWM, Input Capture and Output compare, I2C, SPI, ADC)

Not supported yet:

• Sub-1 GHz Transceiver
• 125 kHz RFID
• NFC
• Infrared Transceiver
• iButton

For more BSP details see BoardSupportPackage.

• OLED Display 128x32, 128x64, I2C
• E-Ink FeatherWing 250x122 SPI
• NeoPixel
• CharlieWing
• NeoPixelWing
• DotStarWing

These instructions will get you a copy of the project up and running on your local machine (Flipper Zero) for development and testing purposes.

• Flipper Zero with STM32WB55 MCU (Cortex ARM M4) runs at a 32 MHz (the Bluetooth stack runs on a Cortex ARM M0+ core).
• Optional: ST-Link V3 Developer Board or you can build your own e.g. with a STLINK-V3MINI and some cables, see JTAG_SWD_Adaptor
• Terminal emulator application for PC, e.g.:
  • tio my favourite, find your device ID with tio -L and connect to it tio --map ICRNL,INLCRNL /dev/serial/by-id/usb-TinyUSB_TinyUSB_Device_550039001850503542363220-if00
  • PuTTY - Windows and Linux
  • Tera Term - Windows
  • Realterm - Windows
  • minicom, microcom, screen - Linux
  • Use the built in Eclipse console (but no LF)
  • for details see Terminal IO
• STM32CubeProgrammer or qFlipper

Flash the Mecrisp-Cube binary MecrispCubeFlipper.bin or better the fs-binary MecrispCubeFlipperFS.bin to the Flipper Zero. Using the built-in USB DFU bootloader, see also firmware recovery.

1. Press and hold the OK and the back buttons for 30 s (you should see a blank screen)
2. Connect the Flipper Zero USB to the PC
3. Program the binary (MecrispCubeFlipper.bin or better MecrispCubeFlipperFS.bin) with
   1. the STMCubeProgrammer (select USB Device), for Linux sudo /usr/local/STMicroelectronics/STM32Cube/STM32CubeProgrammer/bin/STM32CubeProgrammer
   2. or the qFlipper with install from file
4. Reboot your device by pressing and holding the left and back buttons

Connect the Flipper Zero USB to the PC. Start the terminal emulator application on the PC. Check for the serial communication port (e.g. for Linux /dev/ttyACM0). I set the putty terminal configuration to

• Implicit CR in every LF
• Local echo: off
• Local line editing: off
• Keyboard Backspace: Control-H
• Keyboard Function: Keys VT100
• Remote character set: CP850

The greeting screen should apear after startup:

Mecrisp-Cube 1.6.0 rel for STM32WB Flipper, 63/128  KiB RAM/FLASH dictionary (C) 2024 peter@spyr.ch
  * Mecrisp-Stellaris RA 2.5.4 by Matthias Koch. 
  * Firmware Package STM32Cube FW_WB V1.17.3, BLE Stack 5.3 (C) 2023 STMicroelectronics 
  * CMSIS-RTOS V2 FreeRTOS wrapper, FreeRTOS Kernel V10.3.1 (C) 2020 Amazon.com
  * FatFs for internal flash and microSD - Generic FAT fs module  R0.12c (C) 2017 ChaN
  * tiny vi - part of BusyBox (C) 2000, 2001 Sterling Huxley
  * TinyUSB CDC, MSC v0.16.0 (C) 2023, hathach (tinyusb.org)

include 0:/etc/rc.local 

Use the interpreter (reverse polnish notation, like HP calculators):

23 5 / .

This looks like this on your terminal (bold is the Forth answer):

23 5 / .[CR] 4  ok.

The ok. is the Forth prompt and apears at the end of the line (Forth does it differently, like most things ;-). If you don't like it, change it. [CR] is the Enter-key.

Type in your first Forth program (create a word in the RAM dictionray):

: hello ." World" ;

and execute the the program

hello 

again the terminal output:

: hello ." World" ;[CR]  ok.
hello[CR] World ok.

The program hello ist not persistent, after power cycle or even reset the RAM dictionray is erased. But it is easy to add a word to the Flash dictionray:

compiletoflash
: hello ." World" ;

The program source is not saved, only the executable machine code is compiled into the flash. You can use the built-in editor vi and save your source to the filesystem either on internal flash drive 0: or on the microSD card drive 1:.

The following part is only for people who are interested how Forth works and have knowledge about the ARM Assembler. There is a built-in disassembler (consider the machine code B500 is 16 bit hex number, but it is stored as 00 B5):

see hello
08043558: B500  push { lr }
0804355A: F7BF  bl  08002BE4  -->  .' World'
0804355C: FB43
0804355E: 5705
08043560: 726F
08043562: 646C
08043564: BD00  pop { pc }

The dictionray entry looks like this (you can see the 'hello' and the string constant 'World'):

$08043558 10 dump
08043550 :  00 00 05 68 65 6C 6C 6F   00 B5 BF F7 43 FB 05 57  | ...hello  ....C..W |
08043560 :  6F 72 6C 64 00 BD 00 00   FF FF FF FF FF FF FF FF  | orld....  ........ |

The compiled word hello needs only 14 bytes in the dictionary.

• Switch Off press and hold the BACK-Button for 5 s or type in the command shutdown
• Switch On press the BACK-Button
• Reset press and hold the BACK- and LEFT-Button or Ctrl-C or reset

USB-CDC is the default console.

• Button UP CRS (Bluetooth Cable Replacement Service) is standard console
• Button DOWN UART is standard console
• Button RIGHT do not include 0:/etc/rc.local

The RGB LED displays the status

• dimmed Green LIPO fully charged
• dimmed Red LIPO charging
• dimmed Blue BLE connected
• flashing Green "disk" (serial flash or SD) write operation
• flashing Yellow "disk" (serial flash or SD) read operation

If you want to go back to the original firmware, do the following

1. Press and hold the OK and the back buttons for 30 s (you should see a blank screen)
2. Connect the Flipper Zero USB to the PC
3. Flash the Flipper firmware with qFlipper REPAIR
4. Reboot your device by pressing and holding the left and back buttons

A step by step series of examples that tell you how to get a development env running

Install the IDE STM32CubeIDE, it is Eclipse and GCC based. STM32CubeMX is included in the IDE, you need a stand alone installation only if you do not want to use the STM32CubeIDE.

Get the sources from github:

$ git clone https://github.com/spyren/Mecrisp-Cube
Cloning into 'Mecrisp-Cube'...
remote: Enumerating objects: 8334, done.
remote: Counting objects: 100% (2220/2220), done.
remote: Compressing objects: 100% (860/860), done.
remote: Total 8334 (delta 1458), reused 2059 (delta 1335), pack-reused 6114
Receiving objects: 100% (8334/8334), 108.93 MiB | 13.49 MiB/s, done.
Resolving deltas: 100% (5788/5788), done.
$ mv Mecrisp-Cube MecrispCubeFlipper
$ cd MecrispCubeFlipper
$ checkout Flipper
Switched to a new branch 'Flipper'
branch 'Flipper' set up to track 'origin/Flipper'.

Import the project into the IDE:

File -> Import -> General -> Existing Projects into Workspace -> Select root directory
Copy project into workspace
Browse to MecrispCubeFlipper directory

Generate code from the STM32CubeMX MecrispCubeFlipper.ioc file:

Project -> Generate Code 

Restore changed source files

$ git status
{list of changed files}
$ git restore {files to restore} 

alternative

$ git stash

Select the Build Configuration (Debug if you want to debug the project) and Build the project:

Project -> Build Configurations -> Set Active -> Debug/Release 
Project -> Build Project

• STM32CubeIDE - STM32CubeIDE is an all-in-one multi-OS development tool, which is part of the STM32Cube software ecosystem. The IDE is used for development, GCC tools are included.
• STM32CubeMX - STM32CubeMX is a graphical tool that allows a very easy configuration of STM32 microcontrollers and microprocessors, as well as the generation of the corresponding initialization C code for the Arm® Cortex®-M core or a partial Linux® Device Tree for Arm® Cortex®-A core), through a step-by-step process.
• STM32CubeProg - STM32CubeProgrammer (STM32CubeProg) is an all-in-one multi-OS software tool for programming STM32 products.

The STM tools work on Linux, Windows, and Mac.

Tab size is 4 for C and assembler source files. Append ?ts=4 to the URL to change the tab-size.

We use SemVer for versioning. For the versions available, see the tags on this repository.

• USART0 default terminal console, 115200 Baud, 20 KiB Rx buffer
• USB-CDC secondary terminal console, type cdc to change console, back with uart.
• 512 KiB Flash dictionary, 60 KiB RAM dictionary

• CMSIS-RTOS, FreeRTOS Kernel V10.2.1
• FatFs R0.12c, some Unix like command line tools
• BLE Cable Replacement Service.

• CMSIS-RTOS, FreeRTOS Kernel V10.2.1
• FatFs R0.12c, some Unix like command line tools
• BLE Cable Replacement Service.
• tiny vi - part of BusyBox

• Mecrisp-Stellaris RA
• Flash Drive
• OLED driver, I2C, timer, RTC
• Markdown docs

• Own Tags for F405 and WB55 chips
• 0:/etc/rc.local startup script
• 2 MiB flash drive for F405

• Support for Floating-Point Unit
• EPD driver
• Watchdog and Asserts

• LCD driver (Flipper)
• Docu on GitHub

• Device USB-CDC and USB-MSC

• Peter Schmid - Initial work - Mecrisp Cube
• Matthias Koch - Forth on ARM Cortex M0/M4 - Mecrisp Stellaris

See also the list of contributors who participated in this project.

This project Mecrsip-Cube is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

Mecrsip-Cube is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with Mecrsip-Cube. If not, see http://www.gnu.org/licenses/.

• http://mecrisp.sourceforge.net/ Original Mecrisp project, Matthias Koch
• https://mecrisp-stellaris-folkdoc.sourceforge.io/ Mecrisp Stellaris Unofficial UserDoc, Terry Porter

• Words, built-in words
• Board Support Package, board specific
• RTOS, CMSIS real-time OS
• Terminal IO
• Filesystem
• VI Editor
• Error Handling (Assertion and Watchdog)
• Real Time Clock
• Floating Point Unit
• C API
• Display

• Leo Brodie, Starting Forth

• Leo Brodie, Thinking Forth

• https://jeelabs.org/article/1612b/ Forth in 7 easy steps, Jean-Claude Wippler

• https://forth-ev.de/ Forth-Gesellschaft e.V.

• https://forth-ev.de/wiki/res/lib/exe/fetch.php/vd-archiv:4d2015-arm.pdf ARM-Sonderheft

• https://forth-standard.org/standard/words, Forth 2012 Standard Words

• https://gforth.org/manual/, GForth Manual