nrf5340 | SAADC ISR blocking ble_data_recieve events.

RE: nrf5340 | SAADC ISR blocking ble_data_recieve events.

Jørgen Holmefjord — Tue, 08 Nov 2022 14:18:21 GMT

Since BLE can only send data at the connection intervals, there should not be any changes in the data output rate. The only difference should be that you will be send more samples in a single transfer instead of sending many smaller packets containing a single sample.

The priority of the timing critical BLE tasks should always be higher than the application interrupts, so I do not think that the SAADC handling itself is blocking any incoming packets. What might be blocking the transfers, however, is the many small packets that you are sending, creating much overhead in transfer time, preventing other BLE activity.

It seems you already have set the SAADC interrupt priority to low (IRQ_PRIO_LOWEST), which should not make it preempt any other tasks than the ones with the same priority (or lower, like main thread).

RE: nrf5340 | SAADC ISR blocking ble_data_recieve events.

mattmacleod — Mon, 07 Nov 2022 16:56:20 GMT

Hi Jargen,

Thank you for your quick reply.

I need an output data rate of 6000Hz for an industrial sensing system that needs to be monitored in Realtime. Wont buffering the sample rate reduce that?

Is there any other way I could unblock the interrupt handler during a BLE receive?

Thanks,

Matt

RE: nrf5340 | SAADC ISR blocking ble_data_recieve events.

Jørgen Holmefjord — Mon, 07 Nov 2022 15:27:20 GMT

Hi,

Do you need to have a buffer size of 1? Since the minimum connection interval of BLE is 7.5ms, you could set the buffer size larger to only get interrupt when the SAADC have sampled multiple samples, and then send the data over BLE as a larger chunk (you should be able to complete ~45 samples during 7.5ms). This will reduce the time that the CPU needs to spend in the SAADC interrupt handler. As the SAADC peripheral support EasyDMA for sampling directly to RAM, and you can set the buffer size up to 16383 samples.

Best regards,
Jørgen