Mecrisp-Cube for the STM32F405 (Adafruit Feather STM32F405 Express)
Intro MecrispCubeF405
A new flavor for Mecrisp-Cube: MecrispCubeF405 for Adafruit's Feather STM32F405.

If you need a faster MCU (168 MHz) and FeatherWings extensions without soldering then the MecrispCubeF405 could be the right Mecrisp Forth for you. There are many stackable boards from Adafruit to choose from: displays, joysticks, actuators, sensors, etc. The only drawback is the lack of BLE, but for this there is a MecrispCubeWB for the STM32WB55. Or if you need even faster MCU, there is MecrispCubeH74x with 480 MHz.

Mecrisp-Cube Instant real-time programming with Forth.

Sources on GitHub (F405 branch on Mecrisp-Cube)


The standard Mecrisp-Cube features like RTOS, Filesystem, USB, etc.

  • 32 KiB RAM dictionary Yes / Done, CCM (core coupled memory) unfortunately can not be used either for code or DMA.
  • 768 KiB Flash dictionary Yes / Done
  • Internal Flash drive 0:, 2 MiB
  • microSD drive 1:
  • BSP BoardSupportPackageF405

Getting Started

These instructions will get you a copy of the project up and running on your local machine (Adafruit Feather STM32F405 Express board) for development and testing purposes.


  • Adafruit Feather STM32F405 Stackable Feather board with STM32F405 MCU runs at a blistering 168 MHz. If you want to debug C and assembler programs you need an ST-Link debugger/programmer.
  • Terminal emulator application for PC, e.g.:
    • PuTTY - Windows and Linux
    • Tera Term - Windows
    • Realterm - Windows
    • minicom, microcom, screen - Linux
    • Use the built in Eclipse console (but no LF)

Flash the Mecrisp-Cube binary (MecrispCubeF405.bin) or the util-binary (MecrispCubeF405Util.bin) to the Feather Board.

  1. Connect the BOOTP (BO Pin) to 3.3V
  2. Connect the Feather Board USB to the PC
  3. Program the binary with the STMCubeProgrammer
  4. Disconnect the BOOTP (BO Pin)
  5. Reset or power cycle the Feather board

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: Auto
  • Local line editing: Auto
  • Keyboard Backspace: Control-H
  • Keyboard Function: Keys VT100
  • Remote character set: CP850

Mecrisp-Stellaris RA 2.5.4 by Matthias Koch.

Mecrisp-Cube 1.4.3 for STM32F405, 31/768 KiB RAM/FLASH dictionary (C) 2021
  * Firmware Package STM32Cube F4 V1.26.0, USB-CDC (C) 2021 STMicroelectronics
  * CMSIS-RTOS V2 FreeRTOS wrapper, FreeRTOS Kernel V10.3.1 (C) 2020
  * FatFs for serial flash and microSD - Generic FAT fs module  R0.12c (C) 2017 ChaN
  * tiny vi - part of BusyBox (C) 2000, 2001 Sterling Huxley

include 0:/etc/rc.local

23 5 / .[CR] 4  ok.
: hello ." World" ;[CR]  ok.
hello[CR] World ok.

Additional Tools and Local Filesystem

Populate a microSD with the contents of sdcard. Put the microSD into the F405 slot and reset or power cycle the board.

The directory should look like this:

ls -l 1:[CR]
drw-         0 2021-04-18T18:12:38 boot
drw-         0 2021-03-21T18:47:52 etc
drw-         0 2021-03-21T18:47:54 fsr
drw-         0 2021-03-21T18:47:54 home
drw-         0 2021-03-21T18:47:56 man
-rwa      7219 2021-01-08T19:42:36

You can use the local CLI commands like mkfs, mkdir and cp to create a filesystem on the serial flash and fill it with files and folders. But this is tedious job because I haven't yet implemented a recursive copy for MecrispCube. But there is prepared disk image (for details see MicroSdBlocks#Serial_Flash) on microSD and the tool dd. You can copy the disk image to the drive 0: (this takes about 2 Minutes):

dd 1:/boot/fd-2MiB.img 0:[CR]
mount 0:[CR]
ls 0:[CR]
man                     fsr                          boot
etc                     home

The Mecrisp have some tools bundled in its distribution e.g. assembler, disassembler, dump, float. I put those tools and some more into the folder /fsr. With the "init.fs script" I compile my favorite ones into the flash directory:

compiletoflash[CR]  ok.
include /etc/init.fs[CR]
init.fs Loading started
RAM Dictionary: 392991 KiB
utils.fs loading ...
conditional.fs loading ...
dump.fs loading ...
disassembler-m3.fs loading ...
float.fs loading ...
threads.fs loading ...
RAM Dictionary: 392981 KiB
init.fs finished  ok.

For example, the word disassember is available now:

see dump[CR]
080405F0: B500  push { lr }
080405F2: F7C2  bl  08002A3E  --> cr
080405F4: FA24
080405F6: CF08  ldmia r7 { r3 }
080405F8: F013  ands r2 r3 #F
080405FA: 020F
080405FC: F847  str r3 [ r7 #-4 ]!
080405FE: 3D04
08040600: 2A00  cmp r2 #0
08040602: D000  beq 08040606
08040604: 3610  adds r6 #10
08040606: CF08  ldmia r7 { r3 }
08040608: F847  str r6 [ r7 #-4 ]!


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:

psi@homer:~> git clone --branch F405
Klone nach 'Mecrisp-Cube' ...
remote: Enumerating objects: 1157, done.
remote: Counting objects: 100% (1157/1157), done.
remote: Compressing objects: 100% (620/620), done.
remote: Total 3183 (delta 720), reused 934 (delta 525), pack-reused 2026
Empfange Objekte: 100% (3183/3183), 41.60 MiB | 6.96 MiB/s, Fertig.
Löse Unterschiede auf: 100% (2100/2100), Fertig.

Import the project into the IDE:

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

Generate code from the STM32CubeMX MecrispCubeF405.ioc file:

Project -> Generate Code 

Restore changed source files

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

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

-- Peter Schmid - 2020-04-11

Creative Commons License
This work by Peter Schmid is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

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