MM32SPIN27 arduino

Because of cost or supply problems, people look for alternatives to well-established microcontrollers. The MindMotion MM32SPIN27 is a low-cost Arm Cortex-M0 microcontroller with a pin-out compatible with the STM32F103. The MM32SPIN27 is an alternative to the STM32F103, if your application

• does not need USB
• does not need VBAT battery-backup
• does not need hardware FPU floating point unit (software floating point is OK)
• does not need EEPROM (storing settings in flash is OK)
• needs only 12 kbyte RAM or less

This is an arduino for MM32SPIN27 and MM32SPIN25 processors.

• MM32SPIN27: 128kbyte flash, 12kbyte ram, 96MHz
• MM32SPIN25: 32kbyte flash, 8kbyte ram, 96MHz

This is modest but sufficient to write small projects. As a demo project, see the t12-958 soldering iron controller.

compiling

• Install arduino IDE
• In File ⇨ Preferences... ⇨ Additional Board Manager URLs, put the URL of the package_seekfree_index.json file: https://raw.githubusercontent.com/koendv/MM32SPIN27-Arduino/main/package_seekfree_index.json
• close and restart arduino IDE.
• for hardware division, copy the file libgcc.a: cp mm32-libgcc/libgcc.a ~/.arduino15/packages/SeekFree/tools/xpack-arm-none-eabi-gcc/10.3.1-2.3/lib/gcc/arm-none-eabi/10.3.1/thumb/v6-m/nofp/libgcc.a
• in the upper left, in Select other board and port... type: MM32SPIN27
• in File ⇨ Open... choose the project. Example: t12-958.ino
• choose Sketch... ⇨ Verify/Compile
• upload firmware using a debugger (H7-Tool, black magic probe, JLink) or using the serial port (pin BOOT0 high).

development platform

Arduino IDE 2.0 and arduino-cli is used.

linux

Linux is used as development platform. Files are case-sensitive. For best results, use a debian-based linux.

windows

To successfully compile on Windows, directories need to be configured as case-sensitive. Else the system does not distinguish between "String.h" and "string.h".

On Windows, arduino stores the MM32SPIN27 files under the directory C:\Users\Name\AppData\Local\Arduino15\packages\SeekFree, where Name is your Windows user name. To make this directory and subdirectories case sensitive:

• in File Explorer, go to C:\Users\Name\AppData\Local\Arduino15\packages
• compress the SeekFree folder to SeekFree.zip
• delete the SeekFree folder
• create an empty SeekFree folder
• run PowerShell as Administrator and at the command prompt type:

Enable-WindowsOptionalFeature -Online -FeatureName Microsoft-Windows-Subsystem-Linux
fsutil.exe file setCaseSensitiveInfo "C:\Users\Name\AppData\Local\Arduino15\packages\SeekFree" enable

• unzip SeekFree.zip

The SeekFree directory and the files and subdirectories in the SeekFree directory are now case-sensitive.

hardware acceleration

MM32SPIN27 is an Arm Cortex-m0 processor. Cortex-M0 has no hardware FPU, no division instruction. However, MM32SPIN27 has hardware acceleration for 32-bit integer division and remainder, integer square root and crc.

On a small processor like this, if there is hardware support for something, it's there for a reason. Use it.

hardware division

Standard libgcc on Cortex-M0 uses software integer division. Division in software works, but is slow. Using hardware division speeds up execution noticeably. This software patches libgcc to use MM32 hardware support for 32-bit signed and unsigned integer division. If you wish to use hardware division you have to replace the compiler libgcc.a by the patched version. See directory mm32-libgcc

There is a small complication. Hardware division needs the AHB clock to function. So after replacing libgcc.a the operators / and % can not be used before system clock initialization. In particular, SetSysClock() has been patched not to use division / to calculate PLL settings.

Other operands, such as + - * work normally.

hardware crc and square root

Support for hardware crc is through the arduino library HWCRC. Only one crc32 algorithm is supported. See hwcrc_performance.ino for a speed comparison between software crc and hardware crc.

Support for hardware integer square root is the arduino library HWSQRT.

functions

The following functions were ported to MM32SPIN27:

• attachInterrupt(), detachInterrupt()
• analogRead(), analogReadResolution(), analogSampleTime()
• analogWrite(), analogWriteResolution(), analogWriteFrequency()
• digitalWrite(), digitalRead(), digitalToggle()
• millis(), delay(), delayMicroseconds()

The following libraries are included:

• FlashStorage to store settings in flash
• HWCRC CRC32 in hardware
• HWSQRT integer square root in hardware
• RTTStream Segger RTT
• Serial hardware UART
• SoftwareWire I2C in software
• SPI in hardware

This list was determined in the following way: I wrote a demo project. If something was needed, I added it.

demo project

As a demo, a T12 soldering station was implemented. This is an application with an SPI OLED display, a rotary encoder with pushbutton, analog and digital inputs, and PWM output. Standard arduino libraries were used for display, task scheduler, PID controller, and temperature sensors.

free memory

The linker checks there is enough free memory. If you get the following error, there is not enough free memory.

arm-none-eabi/bin/ld: region `RAM' overflowed by 123 bytes
collect2: error: ld returned 1 exit status

To solve this problem, either

• rewrite the program to use less memory, or
• lower the amount of free memory needed. In boards.txt, change MM32SPIN27.build.min_free_ram=3K

firmware download

After successful compilation, binaries are in /home/UserName/Arduino/ProjectName/build/SeekFree.mm32.MM32SPIN27/ProjectName.ino.elf

The compiled firmware can then be downloaded to the MM32SPIN27:

• Segger JLink does not explicitly support MM32SPIN27 but configuring as MM32L072XX works.
• Black Magic Probe supports MM32SPIN27
• H7-Tool supports many "Made in Asia" processors, including MM32.
• AN0006 contains a list of supported debuggers/flashers. (Chinese)
• firmware download via serial port.

compiler version

The compilers from the xpack project are used.

If you wish to change the compiler version: Compiler version is specified twice, once in platform.txt:

compiler.path={runtime.tools.xpack-arm-none-eabi-gcc-10.3.1-1.2.3.path}/bin/

and once in package_seekfree_index.json:

          "toolsDependencies": [
            {
              "packager": "SeekFree",
              "name": "xpack-arm-none-eabi-gcc",
              "version": "10.3.1-2.3"
            },

other processors

This software is for MM32SPIN27. This software can be adapted to other MindMotion MM32 Cortex-M0 processors.

First, in boards.txt change ram size, flash size, minimum free ram, and see if you can run a small arduino sketch to blink a led. Maybe you are lucky.

• boards.txt: set ram size, flash size, minimum free memory.
• package_seekfree_index.json: add board to packages->platforms->boards
• check board definition in variants directory, create new board if necessary
• replace cores/arduino/HAL_Lib with HAL_Lib for the new processor
• replace cores/arduino/MM32SPIN2xx_p with SDK for the new processor
• to add a directory to the include path, in platform.txt add the path to compiler.seekfree.extra_include

References

• MM32SPIN27 datasheet (English)
• MM32SPIN27 product page (English)
• HAL library from MindMotion
• MM32SPIN2x_p_Lib_Samples
• SeekFree library for the MM32SPIN27
• ArduinoCore-API
• mm32_startup
• mm32spin0280_lib_samples Different but similar processor; more source samples.
• 4 channel SPDT relay firmware on MM32SPIN31