Communication between nRF24L01+ and nRF52840 dongle with ESB_DPL. The nRF24L01+ is PTX and the dongle is PRX. Unable to get ack payload working effectively.

[adamvn]

I am only able to successfully trigger the ACK payload interrupt on the nRF24L01+ if I mismatch the payload lengths on the two devices; 4 for the nRF24L01+ and 1 for the nRF52840 dongle.

I have a PCA10028 on an older SDK 12.3 and the communication works fine (nRF51422). 

I use the default ESB settings on each device except that the data rate is 1 Mbps.

[adamvn]

It appears that the turnaround time for the nRF52840 of 250 us was to short. Changing the ARD value in the SETUP_RETR register of the nRF24L01+ to 500us fixed this problem. Didn't expect the newer radio to be slightly slower.