Before RADIO is able to receive a packet, it must first ramp up in RX mode. See RXRU in Radio states 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, the START task can first be triggered after RADIO has entered into the RXIDLE state.
The following figure shows a single packet reception where the CPU manually triggers the different tasks needed to control the flow of RADIO, i.e. 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 END 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 modified version of the receive sequence, where RADIO is configured to use shortcuts between READY and START, and between END and DISABLE, which means that no delay is introduced.
RADIO can receive consecutive packets without having to disable and re-enable RADIO between packets, as illustrated in the following figure.