ST25R3916B with Antenna Multiplexer – RFAL_worker() timing and FreeRTOS task separation?

[MERSI]

Hi everyone,

I’m currently working with the ST25R3916B NFC reader and controlling up to 6 external antennas via a multiplexer. The antennas are activated sequentially, i.e., I switch between them one after another in a polling loop.

However, I’m experiencing an issue where not all antennas work reliably in every cycle. Sometimes an antenna seems unresponsive or is not detected by a test card, even though it worked in earlier cycles.

I suspect that the problem might be related to RFAL_worker() not being called frequently enough.

Could that be the root cause?

My current architecture is based on FreeRTOS, and I’m considering the following approach:

Run RFAL_worker() continuously in a dedicated FreeRTOS task, perhaps at a high frequency or short interval.

Run the other NFC logic (polling, tag handling, antenna switching, etc.) in the main task or another thread.

My questions:

1. Is it safe and recommended to call RFAL_worker() in a separate FreeRTOS task while performing the rest of the NFC logic in another task?

2. Do I need to use mutexes or other synchronization mechanisms to protect access to shared RFAL state? 

3. Has anyone successfully implemented a similar architecture with the ST25R3916 and multiple antennas?

Any input, guidance, or example setups would be greatly appreciated!

Thanks in advance

[Brian TIDAL · Accepted solution]

Hi,

The FreeRTOS_polling demo in the ST25R Embedded Library provides an example of the RFAL operating under FreeRTOS.

The application and the RFAL operate within the same task. An ISR task with a higher priority manages the ST25R3916B interrupt pin. This ISR task is notified by the interrupt handler using vTaskNotifyGiveFromISR.

The communication with the ST25R3916B is safeguarded using taskENTER_CRITICAL() and taskEXIT_CRITICAL().

It is recommended to follow this software architecture.

Rgds

BT