When can the PACKETPTR register be updated?

[abkirchhoff]

I am using the radio in the nRF52832 to support a custom protocol. I would like to send two packets in a row, each with different payloads, on the same frequency. When can I safely update the PACKETPTR register to point to the new packet contents? After the PAYLOAD event or after the END event?

After the PAYLOAD event would be ideal, as this would allow me to use the END->START shortcut, provided I can update the PACKETPTR register in the time it takes to transmit the CRC. The datasheet actually says to wait until after the DISABLED event, but I am hoping that is not the case.

Thanks!

[Susheel Nuguru]

In this I mentioned that it is safest to update PACKETPTR when you get the disabled event. That is when we are sure that EasyDMA is has finished accessing RAM.

[abkirchhoff]

That makes sense for the receive operation. For a transmit operation, a PAYLOAD event indicates that the payload has been sent over the air. Thus, the packet must have been read from RAM by the time that event occurs. The EasyDMA would be done accessing RAM and the PACKETPTR could be changed. Would you agree with my theory? Am I missing anything?

[Martijn]

In de nrf51 the START task was used as a decision point for the PACKETPTR. Isn't this the same in the nrf52?

If so, the address event should be the first indication it is safe to update the PACKETPTR (the start task is passed). We use this in our nrf51 applications.

I was looking at it right now and noticed there are no mentions of decision points at all in the nrf52 documentation. I guess this should be updated

[Susheel Nuguru]

I am sorry, my last comment got deleted somehow. I will rewrite it

I agree with abkirchhoff, getting PAYLOAD, ADDRESS or END event should theoretically be enough in TX mode to know that the EasyDMA has done fetching the packet from RAM.

@Martijn: I can see that the decision point is little blurry when it comes to TX mode, but for RX you have to wait until you get the DISABLED event.

[Susheel Nuguru]

One update though, The CRC is calculated on the fly in the hardware while TX/RX, So for TX even though we are sure that getting PAYLOAD, ADDRESS or END event marks for sure that EasyDMA is finished but that does not mark the it is safe to update the PACKETPTR because can still be CRC pending.

I think we will stick to what PS says that we need to wait for the DISABLED event and not rely on theories. We would not achieve any significant throughput or power advantages on taking this risk.