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Establishing serial communication over UART instead of USB in MAX25405 EVKIT

rsjawale24

The MAX25405EVKIT comes with a MAX32620FTHR board which is preprogrammed with custom binary file for the gesture recognition. The application note at Maxim Gesture Sensor EVKit Serial API (maximintegrated.com)

mentions "The serial interface can be implemented over the Universal Serial Bus (USB) virtual serial port or over a Universal Asynchronous Receiver-Transmitter (UART). The EV kit is shipped configured to use the USB serial port to work with the EV kit PC Graphical user Interface (GUI). If a UART serial interface is desired, custom firmware in binary format is available."

Upon researching more, I found the firmware_framework code that contains the code for gesture recognition compiled using mbed compiler.

The readme file says that a file called interface.h and interface.c define the communication protocol. When I open the interface.c file, I can see a comment in the code that says Option to implement serial API over UART instead of USB but there is only a MACRO set as #define macro_name 0 

I tried to change the 0 to 1 and compile the code, however, it does not compile successfully. The USBDevice library shows some error while compiling. 

Did anyone try to change the serial API over UART instead of USB? Was it successful?  

EDIT: I have successfully compiled the code for UART. However, I'll do some experiments and write introductory blogs before I re-program the MAX32620FTHR board with my firmware. 

  • I am curious how did you successfully compiled non-changed code? I started working with latest mbed-os but I was unable to compile it (missing toolchain) no matter of USE_UART_INTERFACE setting. Later I found some other issues on internet and general recommendation is downgrade mbed-os because Maxim do not update their codes to last mbed-os and their codes currently do not work with latest mbed-os. After downgrading I was able to successfully compile with USE_UART_INTERFACE set to both 0 and 1.

    I compiled this using following steps. Especially see git checkout which downgrades the mbed-os and description for vim commands in which I had to fix one old py file to work with latest python libraries.

    sudo apt update
sudo apt install python3 python3-pip git mercurial
python3 -m pip install mbed-cli

unzip firmware_framework.zip
rm firmware_framework.zip
mbed new .
mbed add https://os.mbed.com/teams/MaximIntegrated/code/MAX32620FTHR/
mbed add https://os.mbed.com/teams/MaximIntegrated/code/USBDevice/

# add main stack limit section according to readme.txt
vim mbed_app.json

# download ARM GNU Toolchain from https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
tar -xf arm-gnu-toolchain-12.2.mpacbti-bet1-x86_64-arm-none-eabi.tar.xz
export MBED_GCC_ARM_PATH=/home/michal/armgcc/arm-gnu-toolchain-12.2.mpacbti-bet1-x86_64-arm-none-eabi/bin

cd mbed-os
git checkout 0fdfcf7350896a9c0b57c4a18237677abfe25f1a

# in following vim window change following line:
#
# from collections import namedtuple, Mapping
#
# to followiong two lines:
#
# from collections import namedtuple
# from collections.abc import Mapping

vim "/home/michal/max25405fw/mbed-os/tools/targets/__init__.py"

mbed compile -m MAX32620FTHR -t GCC_ARM

    After this I was able to get firmware compiled with both USE_UART_INTERFACE=0 and 1. I currently do not have enough time to test built firmwares. I will test them next weekend. Before flashing I recommend backuping stock firmware. I have not checked on this yet but Maxim usually do not lock MCU for prevent reading stock firmware, so you should be able to download stock firmware from MCU before flashing custom firmware. You should be able to do this using JTAG probe and openocd. Note that vanilla/mainline openocd usually do not work with Maxim MCUs (or at least It never work on my machine and chip). Use their patched openocd which is available as part of their SDKs available at pages of MCUs. As I said, currently I have no time to test it, but next week I will try it and give you better feedback.

  • in reply to misaz

    Hi misaz!

    Thank you for the detailed response. I don't have JTAG and my idea involved communication over UART so I guess I have no other option.

     I did face a few problems while compiling the code as provided by Maxim. 

    I haven't used mbed CLI. I used the mbed online compiler. Just imported the framework to the online compiler and added other required libraries such as the FTHR board files. There were quite a few errors about serial communication and a non void function returning a value. Had fix it up. I flashed my FTHR board with the new binary file and interfaced it with Arduino to read data serially. 

    All I got on the Arduino serial monitor was a value of 240. Not sure what that means. Will have to read the documentation

    It's past midnight now Sunday is already over so I left it as it is. I will look into it tomorrow or next weekend.

    Again, thanks for the tip on retrieving stock firmware. Will try it with some other boards as I've never tried that before.

    Any recommendations on JTAG device? I believe the STM32 discovery board has a JTAG PCB attached to it? Can that be used as a JTAG for other MCUs?

  • in reply to rsjawale24

    You do not need JTAG if you just need to flash firmware. MCU is preprogrammed with bootloader. Hold BOOT button before when connecting USB to computer and device will boot to bootloader and you can drag and drop new firmware.

    I am not sure, but I think that bootloader do not support reading firmware back by any way, so if you want to backup stock firmware then you need to use JTAG probe.

  • in reply to misaz

    Yes, I was asking about JTAG for reading the firmware and keeping a backup. The MCU has a bootloader and can be programmed over usb.

  • in reply to rsjawale24

    STM32 discovery and Nucleo can be used as generic JTAG probe but in case of MAX32620FTHR you will need to DIY connector (except very new discovery boards all older have pinhead and MAX32625 has standard ARM Cortex-M 1.27mm pitch connector) and also level shifting because MAX32620FTHR JTAG use 1.8V and most STM32 Discovery and Nucleo boards use 3.3V.

    I generally recommend using just a bootloader. It is much easier in case of MAX32620FTHR. Now because you flashed it, then you are out of luck with extracting old firmware since it is overwritten now.

  • in reply to misaz

    Yup. Couldn't wait to test out UART so flashed the MCU with new firmware. Will test it out in an hour or so.Hope it will work.  Fingers crossed Fingers crossed

  • in reply to misaz

    I'm curious to know which version of Mbed did you downgrade to as I too could not get it to work with latest version.

    Did you backup stock firmware? I had assumed there was a binary available but alas there was none.

    Just to say that I found a fix for the USBserial (tested version 6.15/6.16), which I highlighted on GitHub ARMmbed issues page: https://github.com/ARMmbed/mbed-os/issues/15334

  • in reply to rsjawale24
    rsjawale24 said:
    All I got on the Arduino serial monitor was a value of 240. Not sure what that means. Will have to read the documentation

    I believe the firmware could be waiting for a command.

    The firmware file cmd.cpp gives clues... although there might also be some documentation online.

      {"ping","Ping the processor.", cmd_ping},
      {"help","Display help.", cmd_help},
      {"ver","Display firmware version", cmd_ver},
      {"reg", "reg <read/write> <addr> <num/value>. Read or write to a device register.", cmd_reg},
      {"stream", "stream <on/off> [nopixels]. Enable data streaming mode. Use nopixels parameter to suppress pixel data.", cmd_stream},
      {"forcecal", "Force bias calibration (tracking mode).", cmd_force_tracking_cal},
      {"reset", "reset device register settings.", cmd_reset},
      {"poll", "Request gesture results", cmd_poll},

  • in reply to misaz

    I tested with Arduino v1.8.16 and you can use the "Burn Bootloader" tool to flash an Arduino compatible bootloader onto the MAX32620FTHR, once you have the board manager files installed.

    PS. You need a separate programmer to do so.

  • in reply to BigG

    The readme file in the framework suggest to use this command

    mbed new . --scm none

    mbed new .
    Use the "--scm none" option to prevent revision control initialization

    Unfortunately, no binary is available for the original firmware. If you have a backup, request you to please share the binary file as I already flashed my MCU with UART firmware