NRF52811-QCAA-R datasheet(87/444 Pages) NORDIC

87 / 444 page

Peripherals

The CCM supports different widths of the LENGTH field in the data structure for decrypted packets. This is

configured in the MODE on page 94 register.

AES CCM

RFU

EPL

L+4 RFU

Unencrypted packet

Encrypted packet

MIC

Scratch area

CCM data

structure

MODE = DECRYPTION

H: Header (S0)

L: Length

RFU: reserved for future use (S1)

PL: unencrypted payload

EPL: encrypted payload

OUTPTR

INPTR

SCRATCHPTR

CNFPTR

Figure 28: Decryption

6.4.4 AES CCM and RADIO concurrent operation

The CCM module is able to encrypt/decrypt data synchronously to data being transmitted or received on

the radio.

In order for the CCM module to run synchronously with the radio, the data rate setting in the MODE on

page 94 register needs to match the radio data rate. The settings in this register apply whenever either

the KSGEN or CRYPT tasks are triggered.

The data rate setting of the MODE on page 94 register can also be overridden on-the-fly during an

ongoing encrypt/decrypt operation by the contents of the RATEOVERRIDE on page 96 register. The

data rate setting in this register applies whenever the RATEOVERRIDE task is triggered. This feature can be

useful in cases where the radio data rate is changed during an ongoing packet transaction.

6.4.5 Encrypting packets on-the-fly in radio transmit mode

When the AES CCM is encrypting a packet on-the-fly at the same time as the radio is transmitting it, the

radio must read the encrypted packet from the same memory location as the AES CCM is writing to.

The OUTPTR on page 95 pointer in the AES CCM must therefore point to the same memory location as

the PACKETPTR pointer in the radio, see Configuration of on-the-fly encryption on page 87.

AES CCM

RFU

EPL

L+4 RFU

Unencrypted packet

Encrypted packet

MIC

Scratch area

CCM data

structure

MODE = ENCRYPTION

RADIO

TXEN

To remote

receiver

H: Header (S0)

L: Length

RFU: reserved for future use (S1)

PL: unencrypted payload

EPL: encrypted payload

INPTR

OUTPTR

PACKETPTR

SCRATCHPTR

CNFPTR

Figure 29: Configuration of on-the-fly encryption

In order to match the RADIO’s timing, the KSGEN task must be triggered early enough to allow the key-

stream generation to complete before the encryption of the packet shall start.

For short packets (MODE.LENGTH = Default) the KSGEN task must be triggered no later than when

the START task in the RADIO is triggered. In addition the shortcut between the ENDKSGEN event and

the CRYPT task must be enabled. This use-case is illustrated in On-the-fly encryption of short packets

(MODE.LENGTH = Default) using a PPI connection on page 88 using a PPI connection between the

READY event in the RADIO and the KSGEN task in the AES CCM.

For long packets (MODE.LENGTH = Extended) the key-stream generation will need to be started even

earlier, for example at the time when the TXEN task in the RADIO is triggered.

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NRF52811-QCAA-R Datasheet(PDF) 87 Page - Nordic Semiconductor

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