ESP32 Forum

Posted: **Tue Oct 23, 2018 8:15 am**

Hi, I'm using an ESP32 in connection with an MPU-9250 to measure acceleration over SPI. Interrupts are used to measure 10'000 samples. Those are sent over WIFI and the process is started again. After around 100+ measurements the sensor suddenly loses accuracy (and also gets a small offset compared to the normal measurement).

This is how it normally looks

: meas1.png (7.54 KiB) Viewed 6332 times

This is how it looks after

: meas2.png (6.98 KiB) Viewed 6332 times

The hex values, depending on the sensors position, look something like this:

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00DF 00DF 00DF 00DF 00E0 00DF 00DF 00DF 00DF 00E0 00E0 00DF 00E0 00DF 00DF 00DF 00E0 00E0 00E0 00DF 00DF 00E0 00DF 00DF

But when I inspect the data coming from the MPU-9250 with an oscilloscope it looks like valid data.

This only happens around 50% of the time, the other 50% the ESP core dumps first. I'm not sure if this is related but I need to fix it as well. This core dump happend after 386 measurements.

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Guru Meditation Error: Core  0 panic'ed (LoadProhibited). Exception was unhandled.
Core 0 register dump:
PC      : 0x40083f0c  PS      : 0x00060031  A0      : 0x4008206d  A1      : 0x3ffb05d0
0x40083f0c: spi_intr at C:/msys32/esp-idf/components/driver/spi_master.c:433

0x4008206d: _xt_lowint1 at C:/msys32/esp-idf/components/freertos/xtensa_vectors.S:1105

A2      : 0x3ffc43a4  A3      : 0x3ffc43b8  A4      : 0x3ffb0570  A5      : 0x3ffc441c
A6      : 0x3ffb8570  A7      : 0x3ffb3684  A8      : 0x80083f05  A9      : 0x9fffcffc
A10     : 0x4001f140  A11     : 0x00000000  A12     : 0xc8746060  A13     : 0x00000001
A14     : 0x00060021  A15     : 0x00060021  SAR     : 0x0000001a  EXCCAUSE: 0x0000001c
EXCVADDR: 0x9fffd104  LBEG    : 0x4000c2e0  LEND    : 0x4000c2f6  LCOUNT  : 0xffffffff
Core 0 was running in ISR context:
EPC1    : 0x40083f0c  EPC2    : 0x00000000  EPC3    : 0x00000000  EPC4    : 0x00000000
0x40083f0c: spi_intr at C:/msys32/esp-idf/components/driver/spi_master.c:433


Backtrace: 0x40083f0c:0x3ffb05d0 0x4008206a:0x3ffb0600 0x4008cf52:0x00000000
0x40083f0c: spi_intr at C:/msys32/esp-idf/components/driver/spi_master.c:433

0x4008206a: _xt_lowint1 at C:/msys32/esp-idf/components/freertos/xtensa_vectors.S:1105

0x4008cf52: xQueueGenericReceive at C:/msys32/esp-idf/components/freertos/queue.c:2037


CPU halted.

Has anyone seen this before?
Please let me know what more information I can provide.

*Edit*: It was different yesterday but today the core dump is much more of an issue than losing the accuracy.

Posted: **Tue Oct 23, 2018 11:55 am**

Post code of your SPI driver (if any apart from IDF) and the functions using this SPI driver.

Posted: **Wed Oct 24, 2018 2:28 am**

Agreed. Smells like a SPI transaction struct somehow got corrupted.

Posted: **Wed Oct 24, 2018 7:05 am**

Hi, thanks for your help. Here is the SPI code.

*Edit* Made some changes to the code, performance and readability should be better now. Problem still persists, especially the one from the post below.

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//This function is called with every interrupt
static void IRAM_ATTR mpu_isr(void *discard)
{
  spi_transaction_t t = {};
  uint8_t tx_buffer[2] = {0x00, 0x00};
  t.length = 2 * 8;
  t.flags = SPI_TRANS_USE_RXDATA; 
  t.tx_buffer = tx_buffer;
  t.cmd = MPUREG_ACCEL_XOUT_H | READ_FLAG;                                      
  spi_device_queue_trans(mpu9250_spi_handle, &t, 0);
}

void task_mpu9250(void *pvParameters)
{
  // Create a queue capable of containing 20 int16 values.
  data_queue = xQueueCreate(20, sizeof(int16_t));

  mpu9250_init_spi();
  // Check if connection to Sensor is ok
  if (mpu9250_whoami())
  {
    mpu9250_init();
    gpio_set_intr_type(PIN_MPU_INT, GPIO_INTR_NEGEDGE); 
    gpio_install_isr_service(0);
    gpio_isr_handler_add(PIN_MPU_INT, mpu_isr, (void *)PIN_MPU_INT);
  }
  vTaskDelete(NULL);
}

// This is called as a post SPI transaction 
static void IRAM_ATTR mpu9250_post_spi_trans(spi_transaction_t *t)
{
  BaseType_t xHigherPriorityTaskWoken;

  if (t->cmd == (MPUREG_ACCEL_XOUT_H | READ_FLAG))
  {
    //Writes x-values into data_buffer and sends them to the queue
    data_buffer = ((int16_t)t->rx_data[0] << 8) | t->rx_data[1];
    xQueueSendToBackFromISR(data_queue, &data_buffer, &xHigherPriorityTaskWoken);
  }
}

void mpu9250_init_spi()
{
  esp_err_t ret;
  spi_bus_config_t buscfg = {.miso_io_num = PIN_SPI_SDI,
                             .mosi_io_num = PIN_SPI_SDO,
                             .sclk_io_num = PIN_SPI_SCK,
                             .quadwp_io_num = -1,
                             .quadhd_io_num = -1};
  spi_device_interface_config_t devcfg = {
      .command_bits = 8,                
      .dummy_bits = 0,                  
      .mode = 3,                        
      .clock_speed_hz = 1000000,       
      .spics_io_num = PIN_MPU_CS,     
      .queue_size = 7,                 
      .post_cb = mpu9250_post_spi_trans 
                                       
                                        
  };
  ret = spi_bus_initialize(HSPI_HOST, &buscfg, 1); 
  assert(ret == ESP_OK);
  ESP_LOGI(TAG, "... Initializing bus.");
  ret = spi_bus_add_device(HSPI_HOST, &devcfg, &mpu9250_spi_handle);
  assert(ret == ESP_OK);
  ESP_LOGI(TAG, "... Adding device bus.");
}

Posted: **Thu Nov 01, 2018 3:28 pm**

Anyone sees a problem with the code?

Something else I've got is that from time to time the sensor returns a value of exactly 0

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t->rx_data[0] = 0

which is not correct. When I analyze the data on the SPI bus with an oscilloscope there is always a value returned.

Edit: Problem has been solved by using spi_device_polling_transmit() instead of spi_device_queue_trans()

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