SPI blocking or nonblocking?

[Emil]

Just to make sure: Will The spi_master_send_recv return when it is done writing and reading, or do you have to have some event wait functionality listening to SPI_MASTER_EVT_TRANSFER_COMPLETED ? I guess it is blocking because you have an output buffer as well...

I am going to do large burst reads having <= 24576 bytes. Is it even possible to read that much in one go memory wise?

Thanks!

[Susheel Nuguru]

The spi_master_send_recv function will only transmit first bytes to start the transaction and then return. This is non blocking.

After the bytes are received for the transmitted first bytes then the rest of the transaction happens in the interrupt context. When the interrupt context has started for the first time you get a SPI_MASTER_EVT_TRANSFER_STARTED event and when the whole transaction is finished then you get SPI_MASTER_EVT_TRANSFER_COMPLETED event.

[Emil]

Thanks!!! I need to make this a blocking function. What is the best way to block it? In windows you have events that you wait for and signal. Should I use IRQs in this context? Or a sleep + a volatile bool (not preferred) ?

[Susheel Nuguru]

In the event callback function that you register using spi_master_evt_handler_reg you can enable a flag (bool) when you get SPI_MASTER_EVT_TRANSFER_COMPLETED. You can wait for this flag to be set in your main context. You can even sleep as the event handler callback is called in interrupt context so the chip will wake up after completion. Make sure you use WFE instead of WFI

[Emil]

Thanks!

The callback function is in place, and it is waiting. I was thinking more of nrf_delay_us as "sleep". I feel that it's "dirty" to sleep and check a volatile bool if it's done. Is there some Event framework I can use for signaling it from the SPI callback ? Like:

wait_for_event(_eventObject, timeout);

.....

Handler:

signal_event(_eventObject);

[Susheel Nuguru]

I think checking for a flag and sleeping if not flag not enabled is not dirty. It takes just few ARM instructions to do it. it makes the logic simple too and this method does not effect power consumption. There is scheduler but that also does indirect signalling only if main is polling .

[Susheel Nuguru]

Emil, could you please update this thread with latest info, if this answer helped you then please click the ✓ to the left of the answer so that others can come and look here.