nrf23L01+ lost ACK payload packets

RE: nrf23L01+ lost ACK payload packets

jrowe — Wed, 25 May 2016 20:35:25 GMT

fixed it by changing my interrupt priorities and adding a counter to my packets - apparently using china as a scapegoat isn't always the best solution. Who knew?

RE: nrf23L01+ lost ACK payload packets

jrowe — Wed, 25 May 2016 18:47:29 GMT

To be clear, do I need to manually re-send my ack packets if the TX_DS bit is not set on the PRX device, or will the PRX re-send the data automatically if the bit is not set? Thanks again.

RE: nrf23L01+ lost ACK payload packets

jrowe — Wed, 25 May 2016 18:09:46 GMT

Thanks for the info Håkon. Our system seems to be missing a lot of ack packets. Our boards were populated in china, so this makes me suspect that they gave us fake knockoff radios that don't deal with ack packets correctly. Is there any way to check whether the PRX is properly checking packet IDs and re-transmitting lost ack packets?

RE: nrf23L01+ lost ACK payload packets

Håkon Alseth — Fri, 03 Oct 2014 13:59:34 GMT

Hi,

ACK_PLD is the internal buffer which is filled by SPI command "W_ACK_PAYLOAD". If you have filled the TX FIFO with one payload (regardless of ACK-payload or normal payload), the TX_EMPTY bit in the FIFO_STATUS register will be '0'.

An ACK-payload is uploaded using the SPI command "W_ACK_PAYLOAD", which is written into the nRF just as a normal payload. MAX_RT is an interrupt that only a transmitter will see. A device configured as a receiver will not see this interrupt.

The problem with an ACK payload is that you will not get an ACK on the ACK-payload (weird sentence, I know). How this is handled inside the radio state machine is that there is a PID field which is a 2 bit counter. This counter will increment for each new packet so that the receiver can will be able to interpret a new packet from a re-transmission. This way, the ACK payload will give the receiver a "TX_DS" interrupt, however; the TX_DS signal will only occur on the next payload:

PTX sends payload #1
PRX receives, and sends ACK-payload

In this scenario, the PRX does not know if the ACK-payload was successfully. On the next payload sent, this will happen:

PTX sends payload #2 and PID counter is incremented.
PRX receives, both "RX_DR" and "TX_DS" will be set in the STATUS register.

If the PTX lost the ACK-payload from the PRX, the PTX will send a re-transmit which the PRX will interpret and re-send the ACK-payload.

The PRX will only forget the ACK-payload once the PID field has incremented (the next PTX payload) and reports "TX_DS" up to the application, meaning that the PTX has successfully received the previous ACK-payload.

Hope this makes sense.

Cheers, Håkon