The OBSERVE_TX register counts the number of packets that a transmitter has retransmitted or dropped.


This table is copied from the nRF24L01 product specification (page 55).

Reset Value
Type Description
PLOS_CNT 7:4 0000 R Count lost packets. The counter is overflow protected to 15, and discontinues at max until reset. The counter is reset by writing to RF_CH.
ARC_CNT 3:0 0000 R Count retransmitted packets. The counter is
reset when transmission of a new packet starts.


PLOS_CNT can be used along with a running count of transmission attempts to determine the packet loss rate.

The ARC_CNT value is used to determine when a packet is lost.  When ARC_CNT equals the value of ARC set in the SETUP_RETR register, the packet being transmitted is considered lost, PLOS_CNT is incremented, and the MAX_RT interrupt fires (not necessarily in that order).

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