Before RADIO is able to receive a packet, it must first ramp up in RX mode. See RXRU in Radio states without PLL and Receive sequence for more information.
An RXRU ramp-up sequence is initiated when the RXEN task is triggered. After RADIO has successfully ramped up, it will generate the READY event indicating that a packet reception can be initiated. A packet reception is initiated by triggering the START task. As illustrated in Radio states without PLL, the START task can first be triggered after RADIO has entered the RXIDLE state.
The following figure shows a single packet reception where the CPU manually triggers the tasks needed to control the flow of RADIO, meaning no shortcuts are used. If shortcuts are not used, a certain amount of delay caused by CPU execution is expected between READY and START, and between PHYEND and DISABLE. RADIO will be listening and possibly receiving undefined data, represented with an X, from START and until a packet with valid preamble (P) is received.
The following figure shows a receive sequence where no delay is introduced. RADIO is configured to use shortcuts between READY and START, and between PHYEND and DISABLE.
RADIO can receive consecutive packets without having to disable and re-enable RADIO between packets, as illustrated in the following figure.