BeanMPX-STM32

Implementation of Toyota's Bean MPX protocol on the STM32

Ported from the AVR https://github.com/specadmin/toyota-mpx/tree/master

Electrical interface

MPX_RX must be connected to a GPIO input configured as an external interrupt, capable of triggering on rising and falling edges. MPX_TX can be any GPIO output.

Code

Clone the repository into your project directory (usually under the Drivers folder), and include in the compilation paths.

Label one GPIO input pin as MPX_RX and set it as an external interrupt on rising and falling edges. Label another GPIO output pin as MPX_TX.

Create a timer that has a frequency which will produce integers for the timing of a full bit and half bit at 10kbps, with an interrupt in CubeIDE. For example with a 160Mhz peripheral clock:

F_CLK = 160000000 hz

MPX_BAUD = 10000 bps

PSC = 7

ARR = 65535 (Set to the maximum value, the driver will auto adjust this as required to the full and half bit values below)

Full Bit = F_CLK / (PSC + 1) / MPX_BAUD - 1 = 1999

Half Bit = F_CLK / (PSC + 1) / MPX_BAUD / 2 - 1 = 999

(Optional) Setup the CRC peripheral to have a length of 8-bits, a polynomal of X4+X1+X0, default value of 0, and input data format in bytes.

Set the following definitions in main.h

#define MPX_TIM_HANDLE htim16 /*Set to the timer handle*/
#define MPX_CLK 20000000UL /*Frequency of each count for the timer referred to by MPX_TIM_HANDLE, ie FCLK / (PSC + 1)*/
#define MPX_CRC_HANDLE hcrc /*If your STM32 has hardware CRC, otherwise comment out to disable hardware crc*/

Include mpx.h in your main.c and setup the interrupt handlers in main.c to call mpx_rx_interrupt() on the rising and falling edges of the MPX_RX pin and mpx_timer_interrupt() when the timer referred to by MPX_TIM_HANDLE overflows.

Initialise the MPX driver calling mpx_init() with an optional callback function that is invoked upon recieving valid frames.

Use mpx_send() to send data on the bus, with an optional callback.

Sample main.c

#include "main.h"
#include "mpx.h"

...

void HAL_GPIO_EXTI_Falling_Callback(uint16_t GPIO_Pin) {
  switch(GPIO_Pin) {
    case MPX_RX_Pin:
      mpx_rx_interrupt();
      break;
    default:
      break;
  }
}

void HAL_GPIO_EXTI_Rising_Callback(uint16_t GPIO_Pin) {
  switch(GPIO_Pin) {
    case MPX_RX_Pin:
      mpx_rx_interrupt();
      break;
    default:
      break;
  }
}

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef* htim) {
  if(htim == &MPX_TIM_HANDLE) {
    mpx_timer_interrupt();
  }
}

void mpx_rx(uint8_t size, const uint8_t* buff) {
  printf("MPX RX: %d |", size);
  for (uint8_t i = 0; i<size; i++) {
    printf(" %#02x", buff[i]);
  }
  printf("\n");
}

void mpx_tx(uint8_t result) {
  printf("MPX TX Status: %d\n", result);
}

...

int main(void) {
  HAL_Init();

  ...

  uint8_t engTemp[]  =  {0x2C, 0xA5}; //Send data to move the engine temperature needle to 165 degrees
  mpx_init(mpx_rx);
  while(1) {
    mpx_send(0xFE, sizeof(engTemp), engTemp, mpx_tx);
    HAL_Delay(250);
  }
  return 0;
}