NRF_ERROR_BUSY for I2C read inside an RTOS thread

[morpho]

In the task, when I do a TWI read via nrf_drv_twi_rx(), in the second iteration of the thread, the driver function returns NRF_ERROR_BUSY.

Is it that the driver takes longer than how fast the thread runs thus initiating a second read even though the previous read transfer wasn't even done?

I'm basing it off the frequencies: Tick ISR runs at 1ms, and an I2C read takes ~5 read cycles (WRITE, ACK, READ, DATA#1, DATA#2) assuming i'm reading two bytes.

Following is a snippet:

void SystemTask::mainThread()
{       
    while(true)
    {
        A.xferData();
        A.read(); 
    }
}

uint16_t A::read()
{
     m_xfer_done = false;
    ret_code_t err_code = nrf_drv_twi_rx(&m_twi, ADDR, _buffer, 2);

    APP_ERROR_CHECK(err_code);   // errors out here!

    while(!m_xfer_done);

    return _value;	         
}

[Susheel Nuguru]

Which RTOS are you running on? Are you using this on top of C++ libraries or are this directly from out SDK?

[morpho]

FreeRTOS. I have C++ wrappers around nRF APIs that are straight out of the SDK. Also I noticed I got around it by having a delay between each read call inside a task via xTaskDelay() so I suspect it has to do with timing

void SystemTask::mainThread() {

  A.xferData(temp, 1);

  while(true) { 
     value = A.read(); 
     vTaskDelay(pdMS_TO_TICKS(1000));

Update: 

With a 1000ms delay between each read, I see the program went into a bad state at some point. Below is the call stack:

[Susheel Nuguru]

That address is Hardfault inside the MBR in Softdevice. I am not sure why this occurs? Can you attach your project for me to test in on my desk?

[morpho]

I am afraid you don't have the sensor it's reading in the system task. Attaching it anyways

SmartWatch 2.zip

[morpho]

now I see this

[Susheel Nuguru]

Disable the logs in sdk_config.h and see if you see the hardfault? Looks like the logs are causing some kind of stack corruption. If disabling logs makes the hardfault goes away, then you should consider checking the stack_size and stack usage of the threads you created-