The MAXLEN field in the PCNF1 register , Ieee802154_250Kbit radio mode

Hi,

The MAXLEN field is described in the EasyDMA chapter in the RADIO documentation:

The radio packets 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 S0LEN field in PCNF0
• LENGTH is configured through the LFLEN field in PCNF0
• S1 is configured through the S1LEN field in PCNF0
• Size of the payload is configured through the value in RAM corresponding to the LENGTH field
• Size of the static add-on to the payload is configured through the STATLEN field in PCNF1

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

Note: The MAXLEN 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 MAXLEN, the RADIO will still transmit or receive in the same way as before, except the payload is now truncated to MAXLEN. The packet's LENGTH field will not be altered when the payload is truncated. The RADIO will calculate CRC as if the packet length is equal to MAXLEN.

Best regards,
Jørgen

Hi, this is the feedback from our HW team:

There is no detailed description of MAXLEN for 802.15.4 in the product specifications, but here are some hints in the Transmit/receive sequence sections with the PACKETPTR:
https://infocenter.nordicsemi.com/topic/ps_nrf52840/radio.html#ieee802154_tx
https://infocenter.nordicsemi.com/topic/ps_nrf52840/radio.html#ieee802154_rx

MAXLEN should cover PHR (1 octet) and the PSDU. The CRC is not written to RAM, but the LQI (in receive mode) is appended (kind of replaces the first byte of the CRC).

Best regards,
Jørgen

Hi, this is the feedback from our HW team:

There is no detailed description of MAXLEN for 802.15.4 in the product specifications, but here are some hints in the Transmit/receive sequence sections with the PACKETPTR:
https://infocenter.nordicsemi.com/topic/ps_nrf52840/radio.html#ieee802154_tx
https://infocenter.nordicsemi.com/topic/ps_nrf52840/radio.html#ieee802154_rx

MAXLEN should cover PHR (1 octet) and the PSDU. The CRC is not written to RAM, but the LQI (in receive mode) is appended (kind of replaces the first byte of the CRC).

Best regards,
Jørgen