ST25R3916B controlled by ESP32 not working

[rbuehlma]

Hi there,

first of all: I'm a software engineer and working with electronics only as a hobbyist. Therefore expect *** errors :)

I'm trying to use a ST25R3916B in my ESP32 project. The I2C communication to the ST25R3916B is working.

The call to rfalNfcInitialize succeeds but the next call to rfalFieldOnAndStartGT causes the ESP32 to crash with a " Core 1 panic'ed (Interrupt wdt timeout on CPU1).". The interrupt is taking too long.

Looking into the code, I found this function:

/*******************************************************************************/
void RfalRfST25R3916Class::st25r3916CheckForReceivedInterrupts(void)
{
  uint8_t  iregs[ST25R3916_INT_REGS_LEN];
  uint32_t irqStatus;

  /* Initialize iregs */
  irqStatus = ST25R3916_IRQ_MASK_NONE;
  ST_MEMSET(iregs, (int32_t)(ST25R3916_IRQ_MASK_ALL & 0xFFU), ST25R3916_INT_REGS_LEN);


  /* In case the IRQ is Edge (not Level) triggered read IRQs until done */
  while (digitalRead(int_pin) == HIGH) {
    st25r3916ReadMultipleRegisters(ST25R3916_REG_IRQ_MAIN, iregs, ST25R3916_INT_REGS_LEN);

    irqStatus |= (uint32_t)iregs[0];
    irqStatus |= (uint32_t)iregs[1] << 8;
    irqStatus |= (uint32_t)iregs[2] << 16;
    irqStatus |= (uint32_t)iregs[3] << 24;
  }

  /* Forward all interrupts, even masked ones to application */
  st25r3916interrupt.status |= irqStatus;
}

Commenting out the call to st25r3916ReadMultipleRegisters solves the crash but will also cause the interrupt to not work anymore (not a surprise).
This function is called by the interrupt and the call to st25r3916ReadMultipleRegisters does some I2C communication which (as far as I understand) should not be done in an interrupt handler.

Is this an incompatibility issue between the STM32duino ST25R3916 library and ESP32? Or am I doing something wrong? Has anyone gotten this IC to work on a ESP32?

Thanks for your time and your help :)

[Brian TIDAL]

Hi,

"Interrupt wdt timeout on CPU1" means a watchdog timeout has occurred. I would suggest to increase the watchdog timeout. 

What is the I2C speed? Using Fast Mode may also help

Rgds

BT

[rbuehlma]

Thanks for the response. Increasing the watchdog timeout is probably not the best way to fix this. A function called by an interrupt should only run for a minimal time and should not do any complex task. I have moved the I2C handling outside the interrrupt function and now it works as expected.

Someone else has also observed the same issue and fixed it in this fork:

https://github.com/mcqn/ST25R3916

Additionally, I created my own fork https://github.com/rbuehlma/ST25R3916 based this one which fixes an issue when using I2C. It also allows to set the I2C address allowing multiple ICs to be used concurrently.