EasyDMA

RADIO uses EasyDMA to read and write packets to RAM without CPU involvement.

As illustrated in RADIO block diagram, the RADIO peripheral's EasyDMA utilizes the same PACKETPTR for receiving and transmitting packets. This pointer should be reconfigured by the CPU each time before RADIO is started by the START task. The PACKETPTR register is double-buffered, meaning that it can be updated and prepared for the next transmission.

The END event indicates that the last bit has been processed by RADIO. The DISABLED event is issued to acknowledge that the DISABLE task is done.

The structure of a packet is described in detail in Packet configuration. The data that is stored in Data RAM and transported by EasyDMA consists of the following fields:

S0
LENGTH
S1
PAYLOAD

In addition, a static add-on is sent immediately after the payload.

The size of each of the listed fields in the frame is configurable (see Packet configuration), and the space occupied in RAM depends on these settings. The size of the field can be zero, as long as the resulting frame complies with the chosen RF protocol.

All fields are extended in size to align with a byte boundary in RAM. For instance, a 3-bit long field on-air will occupy 1 byte in RAM while a 9-bit long field will be extended to 2 bytes.

The packet's elements can be configured as follows:

CI, TERM1, and TERM2 fields are only present in Bluetooth Low Energy Long Range mode
S0 is configured through the field PCNF0.S0LEN
LENGTH is configured through the field PCNF0.LFLEN
S1 is configured through the field PCNF0.S1LEN
Payload size is configured through the value in RAM corresponding to the LENGTH field
Static add-on size is configured through the field PCNF1.STATLEN

The PCNF1.MAXLEN field configures the maximum packet payload plus add-on size in number of bytes that can be transmitted or received by RADIO. This feature can be used to ensure that RADIO does not overwrite or read beyond the RAM assigned to the packet payload. This means that if the LENGTH field of the packet payload exceeds PCNF1.STATLEN, and the LENGTH field in the packet specifies a packet larger than configured in PCNF1.MAXLEN, the payload will be truncated to the length specified in PCNF1.MAXLEN.

Note: The PCNF1.MAXLEN field includes the payload and the add-on, but excludes the size occupied by the S0, LENGTH, and S1 fields. This has to be taken into account when allocating RAM.

If the payload and add-on length is specified larger than PCNF1.MAXLEN, RADIO will transmit or receive in the same way as before, except the payload is now truncated to PCNF1.MAXLEN. The packet's LENGTH field will not be altered when the payload is truncated. RADIO will calculate CRC as if the packet length is equal to PCNF1.MAXLEN.

Note: If PACKETPTR is not pointing to the RAM region, an EasyDMA transfer may result in a HardFault or RAM corruption. See Memory for more information about the different memory regions.

The END event indicates that the last bit has been processed by RADIO. The DISABLED event is issued to acknowledge that the DISABLE task is done.