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Multichannel PWM with the Spresense SDK

  • B

    Hi,
    I have been working on a line following robot with the Spresense camera as the sensor. I have succesfully merged the two examples provided by Sony (DNNRT and the Camera example). Now I want to use PWM to control the motors so that I can configure it's speed. I have been looking into different solutions, but could not find any helpful resources on PWM with 2 channels.

    • I have tried using the PWM example itself and get it to work first. Single channel works like a charm. Sadly I could not find any information about how to enable multi channel operation (there is no information on it on the documentation of the example). I need 2 PWM outputs for 2 motors. The multi channel code is locked behind a parameter called "CONFIG_PWM_MULTICHAN". I have looked at the menuconfig, Kconfig file, the pwm.h library, the config file which defines what to include. I can not find how to enable this option.

    • That is why I decided to delete all instances of this parameter "CONFIG_PWM_MULTICHAN" and all the single channel code with it to force the code to be multi channel. I now get errors every step of the code when I run it.

    • I also tried using the cxd56_pwm.h library and the cxd56_pwm.c file with the functions to create PWM objects (lower half) and use that object to control pwm with the given functions in cxd56_pwm.c such as pwm_setup, pwm_begin, etc.

    I would appreciate it, if I could be pointed towards a way to get PWM working as easy as possible. What would be the best way to use PWM functions? Is there a dedicated library for it? Thanks in advance.

  • K
    DeveloperWorld

    Hi @Berkay-Isik
    Spresense has 4 PWM with 1 channel each:

    /dev/pwm0- pin 6
    /dev/pwm1 - pin 5
    /dev/pwm2 - pin 9
    /dev/pwm3 - pin 3

    If you want 2 PWM outputs, you need to open two devices (open()) and then call ioctl() on each of them.

    You can look at the PWM implementations in CircuitPython: https://github.com/adafruit/circuitpython/blob/main/ports/cxd56/common-hal/pwmio/PWMOut.c

    I hope it will help. If anything is unclear please ask.

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