Need help on NRF24LE1 Auto retransmit & Auto ACK confusions

[junma]

Hi all, Since I will use broadcast way in RF transactions between one NRF24LE1 based senders and serveral NRF24LE1 based receivers. I was told not to use "Auto ACK" in broadcast situation.

Then I have one question, that if I disable "Auto ACK", then can I keep the "Auto Retransmit" feature enabled? And if I set maximum retransmit counts to be 15, can it actually send 15 times in each calling RF_Send() API?

To reduce the data lost, I really need this retransmit feature. Could you please help me about this uncertainty? Thanks in advance!

[Hung Bui]

Hi Junma,

I assume that you don't plan to send data from your receivers to the sender. You can't disable Auto ACK and still have Auto Retransmit.

There are 2 options for you:

• Disable Auto ACK, and send a packet 15 times manually before switch to the new packet.

• Enable Auto ACK and set the number of auto retransmit to 15. Since the receiver only receives, it doesn't mater if you enable Auto ACK or not. But you will consume more power because the transmitter will stay in receiving mode for a while waiting for ACK on each packet.

[junma]

Hi Hung Bui, I was once talked to one NORDIC sales agent, he said if I want to use broadcast way, I shall disable the Auto ACK. And there is another concern, since I introduced the frequency hopping also, I found frequency hopping sometimes will confilict with Auto ACK, I don't know the root cause, but the result are just very instable, and data lost happens often when doing 1 sender to 5 receivers test.

Back to the question, so you mean that if I disable the Auto-ACK, that means the Auto-Retransmit settings are also not work, right?

[Hung Bui]

@junma: Yes, normally when you just want to broadcast, and don't expect any data transmitting back from the peer you should turn off AutoACK (NO_ACK = 1). It's what I suggested at option 1. But you can use option 2 if you want, but it's not recommended. You won't gain anything but more power consumption.

And yes, if you disable Auto-ack (NOACK=1), Auto-retransmit doesn't work. Please have a look at the block diagram at Figure 12 in nRF24LE1 Spec v1.6

[junma]

@Hung Bui Ok, I see. Thank you for all the help!