nRF24L01+ TX/RX interrupt timing jitter

[Thomas K.]

Hi, 

We are using nRF24L01+ modules on an ultrasonic positioning system. For synchronization, we wanted to use the RX and TX interrupts provided by the module to trigger
transmission and reception of ultrasonic pulses. (Transmitter transmits a packet to the receiver -> transmitter begins sending ultrasound pulse at TX, receiver begins
sampling at RX interrupt). However, we are measuring a high jitter in timing between the TX and RX interrupts of up to 1ms. It was our understanding that the state machine
in the nrf is implemented in hardware and therefore the jitter should be rather small. Could this be a configuration issue or is this normal behavior? 

Thank you very much!

[Kenneth]

Hi, are you sending the packets with or without acknowledge? If you are using acknowledge there may be re transmits, both in forward and reverse direction. You may use the noack command to send data without acknowledge, then you may lose packets, but the timing will be accurate when successfully received.

[Thomas K.]

They are sent with acknowledge, I will try to disable the ACK and come back to you, thanks! But shouldn't the TX interrupt only be asserted after the transmit has been successful, i.e. after the ACK has been received? 

[Kenneth]

Yes, but the receiver might have received the packet long time ago (several retransmit periods).

[Kenneth]

There is also a *noack command you can use, so you don't need to disable ack.

[Thomas K.]

That worked, thank you very much!