CCM — AES CCM mode encryption

Cipher block chaining - message authentication code (CCM) mode is an authenticated encryption algorithm designed to provide both authentication and confidentiality during data transfer. CCM combines counter mode encryption and CBC-MAC authentication. The CCM terminology "Message authentication code (MAC)" is called the "Message integrity check (MIC)" in Bluetooth terminology and also in this document.

The CCM block generates an encrypted keystream that is applied to input data using the XOR operation and generates the four byte MIC field in one operation. CCM and RADIO can be configured to work synchronously. CCM will encrypt in time for transmission and decrypt after receiving bytes into memory from the radio. All operations can complete within the packet RX or TX time. CCM on this device is implemented according to Bluetooth requirements and the algorithm as defined in IETF RFC3610, and depends on the AES-128 block cipher. A description of the CCM algorithm can also be found in NIST Special Publication 800-38C. The Bluetooth specification describes the configuration of counter mode blocks and encryption blocks to implement compliant encryption for Bluetooth Low Energy.

The CCM block uses EasyDMA to load key counter mode blocks (including the nonce required), and to read/write plain text and cipher text.

The AES CCM peripheral supports three operations: keystream generation, packet encryption, and packet decryption. These operations are performed in compliance with the Bluetooth AES CCM 128 bit block encryption, see Bluetooth Core specification Version 4.0.

The following figure illustrates keystream generation followed by encryption or decryption. The shortcut is optional.

Figure 1. Keystream generation
Keystream generation

Keystream generation

A new keystream needs to be generated before a new packet encryption or packet decryption operation can start.

A keystream is generated by triggering the KSGEN task. An ENDKSGEN event is generated after the keystream has been generated.

Keystream generation, packet encryption, and packet decryption operations utilize the configuration specified in the data structure pointed to by CNFPTR. It is necessary to configure this pointer and its underlying data structure, and register MODE before the KSGEN task is triggered.

The keystream will be stored in the AES CCM peripheral’s temporary memory area, specified by the SCRATCHPTR, where it will be used in subsequent encryption and decryption operations.

For default length packets (MODE.LENGTH = Default), the size of the generated keystream is 27 bytes. When using extended length packets (MODE.LENGTH = Extended), register MAXPACKETSIZE specifies the length of the keystream to be generated. The length of the generated keystream must be greater or equal to the length of the subsequent packet payload to be encrypted or decrypted. The maximum length of the keystream in extended mode is 251 bytes, which means that the maximum packet payload size is 251.

If a shortcut is used between the ENDKSGEN event and CRYPT task, pointer INPTR and the pointers OUTPTR must also be configured before the KSGEN task is triggered.

Encryption

The AES CCM periheral is able to read an unencrypted packet, encrypt it, and append a four byte MIC field to the packet.

During packet encryption, the AES CCM peripheral performs the following:
  • Reads the unencrypted packet located in RAM address specified in the INPTR pointer
  • Encrypts the packet
  • Appends a four byte long Message Integrity Check (MIC) field to the packet

Encryption is started by triggering the CRYPT task with register MODE set to ENCRYPTION. An ENDCRYPT event is generated when packet encryption is completed.

The AES CCM peripheral will also modify the length field of the packet to adjust for the appended MIC field. It adds four bytes to the length and stores the resulting packet in RAM at the address specified in pointer OUTPTR, see Encryption.

Empty packets (length field is set to 0) will not be encrypted but instead moved unmodified through the AES CCM peripheral.

AES CCM supports different widths of the LENGTH field in the data structure for encrypted packets. This is configured in register MODE.

Figure 2. Encryption
AES CCM packet encryption

Decryption

The AES CCM peripheral is able to read an encrypted packet, decrypt it, authenticate the MIC field, and generate an appropriate MIC status.

During packet decryption, the AES CCM peripheral performs the following:
  • Reads the encrypted packet located in RAM at the address specified in the INPTR pointer
  • Decrypts the packet
  • Authenticates the packet's MIC field
  • Generates the appropriate MIC status

The packet header (S0) and payload are included in the MIC authentication.

Decryption is started by triggering the CRYPT task with register MODE set to DECRYPTION. An ENDCRYPT event is generated when packet decryption is completed.

The AES CCM peripheral modifies the length field of the packet to adjust for the MIC field. It subtracts four bytes from the length and stores the decrypted packet in RAM at the address specified in the pointer OUTPTR, see Decryption.

CCM is only able to decrypt packet payloads that are at least five bytes long (one byte or more encrypted payload (EPL) and four bytes of MIC). CCM will therefore generate a MIC error for packets where the length field is set to 1, 2, 3, or 4.

Empty packets (length field is set to 0) will not be decrypted but instead moved unmodified through the AES CCM peripheral. These packets will always pass the MIC check.

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

Figure 3. Decryption
AES CCM packet decryption

AES CCM and RADIO concurrent operation

The CCM peripheral is able to encrypt/decrypt data synchronously to data being transmitted or received on the radio.

In order for CCM to run synchronously with the radio, the data rate setting in register MODE 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 register MODE can also be overridden on-the-fly during an ongoing encrypt/decrypt operation by the contents of register RATEOVERRIDE. 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.

Encrypting packets on-the-fly in radio transmit mode

When the AES CCM peripheral encrypts a packet on-the-fly while RADIO is transmitting it, RADIO must read the encrypted packet from the same memory location that the AES CCM peripheral is writing to.

The OUTPTR pointer in the AES CCM must point to the same memory location as the PACKETPTR pointer in the radio, see Configuration of on-the-fly encryption.

Figure 4. Configuration of on-the-fly encryption
The OUTPTR pointer in the AES CCM pointing to the same memory location as the PACKETPTR pointer in the RADIO

In order to match RADIO’s timing, the KSGEN task must be triggered early enough to allow the keystream generation to complete before packet encryption begins.

For short packets (MODE.LENGTH = Default), the KSGEN task must be triggered before or at the same time as the START task in 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. It uses a PPI connection between the READY event in RADIO and the KSGEN task in the AES CCM peripheral.

For long packets (MODE.LENGTH = Extended), the keystream generation needs to start earlier, such as when the TXEN task in RADIO is triggered.

Refer to Timing specification for information about the time needed for generating a keystream.

Figure 5. On-the-fly encryption of short packets (MODE.LENGTH = Default) using a PPI connection
KSGEN task triggered not later than triggering of the START task in the RADIO. The shortcut between the ENDKSGEN event and the CRYPT task enabled.

Decrypting packets on-the-fly in RADIO receive mode

When the AES CCM peripheral decrypts a packet on-the-fly while RADIO is receiving it, the AES CCM peripheral must read the encrypted packet from the same memory location that RADIO is writing to.

The INPTR pointer in the AES CCM must point to the same memory location as the PACKETPTR pointer in RADIO, see Configuration of on-the-fly decryption.

Figure 6. Configuration of on-the-fly decryption
The INPTR pointer in the AES CCM pointing to the same memory location as the PACKETPTR pointer in the RADIO

In order to match RADIO’s timing, the KSGEN task must be triggered early enough to allow the keystream generation to complete before the decryption 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 RADIO is triggered. In addition, the CRYPT task must be triggered no earlier than when the ADDRESS event is generated by RADIO.

If the CRYPT task is triggered exactly at the same time as the ADDRESS event is generated by RADIO, the AES CCM peripheral will guarantee that the decryption is completed no later than when the END event in RADIO is generated.

This use-case is illustrated in On-the-fly decryption of short packets (MODE.LENGTH = Default) using a PPI connection using a PPI connection between the ADDRESS event in RADIO and the CRYPT task in the AES CCM peripheral. The KSGEN task is triggered from the READY event in RADIO through a PPI connection.

For long packets (MODE.LENGTH = Extended) the keystream generation will need to start even earlier, such as when the RXEN task in RADIO is triggered.

Refer to Timing specification for information about the time needed for generating a keystream.

Figure 7. On-the-fly decryption of short packets (MODE.LENGTH = Default) using a PPI connection
The CRYPT task triggered at the same time as the ADDRESS event generated by the RADIO. Decryption completed no later than the END event in the RADIO.

CCM data structure

The CCM data structure is located in Data RAM at the memory location specified by the CNFPTR pointer register.

Table 1. CCM data structure overview
Property Address offset Description
KEY 0 16 byte AES key
PKTCTR 16 Octet0 (LSO) of packet counter
  17 Octet1 of packet counter
  18 Octet2 of packet counter
  19 Octet3 of packet counter
  20 Bit 6 – Bit 0: Octet4 (7 most significant bits of packet counter, with Bit 6 being the most significant bit) Bit7: Ignored
  21 Ignored
  22 Ignored
  23 Ignored
  24 Bit 0: Direction bit Bit 7 – Bit 1: Zero padded
IV 25 8 byte initialization vector (IV) Octet0 (LSO) of IV, Octet1 of IV, … , Octet7 (MSO) of IV

The NONCE vector (as specified by the Bluetooth Core Specification) will be generated by hardware based on the information specified in the CCM data structure from CCM data structure overview .

Table 2. Data structure for unencrypted packet
Property Address offset Description
HEADER 0 Packet Header
LENGTH 1 Number of bytes in unencrypted payload
RFU 2 Reserved Future Use
PAYLOAD 3 Unencrypted payload
Table 3. Data structure for encrypted packet
Property Address offset Description
HEADER 0 Packet Header
LENGTH 1

Number of bytes in encrypted payload including length of MIC

LENGTH will be 0 for empty packets since the MIC is not added to empty packets

RFU 2 Reserved Future Use
PAYLOAD 3 Encrypted payload
MIC 3 + payload length

ENCRYPT: 4 bytes encrypted MIC

MIC is not added to empty packets

EasyDMA and ERROR event

CCM implements an EasyDMA mechanism for reading and writing to RAM.

When the CPU and EasyDMA enabled peripherals access the same RAM block at the same time, increased bus collisions might disrupt on-the-fly encryption. This will generate an ERROR event.

EasyDMA stops accessing RAM when the ENDKSGEN and ENDCRYPT events are generated.

If the CNFPTR, SCRATCHPTR, INPTR, and the OUTPTR are not pointing to the Data RAM region, an EasyDMA transfer may result in a HardFault or RAM corruption. See Memory for more information about the different memory regions.

Registers

Table 4. Instances
Base address Peripheral Instance Description Configuration
0x4000F000 CCM CCM

AES counter with CBC-MAC (CCM) mode block encryption

   
Table 5. Register overview
Register Offset Description
TASKS_KSGEN 0x000

Start generation of keystream. This operation will stop by itself when completed.

 
TASKS_CRYPT 0x004

Start encryption/decryption. This operation will stop by itself when completed.

 
TASKS_STOP 0x008

Stop encryption/decryption

 
TASKS_RATEOVERRIDE 0x00C

Override DATARATE setting in MODE register with the contents of the RATEOVERRIDE register for any ongoing encryption/decryption

 
EVENTS_ENDKSGEN 0x100

Keystream generation complete

 
EVENTS_ENDCRYPT 0x104

Encrypt/decrypt complete

 
EVENTS_ERROR 0x108

CCM error event

Deprecated

SHORTS 0x200

Shortcuts between local events and tasks

 
INTENSET 0x304

Enable interrupt

 
INTENCLR 0x308

Disable interrupt

 
MICSTATUS 0x400

MIC check result

 
ENABLE 0x500

Enable

 
MODE 0x504

Operation mode

 
CNFPTR 0x508

Pointer to data structure holding the AES key and the NONCE vector

 
INPTR 0x50C

Input pointer

 
OUTPTR 0x510

Output pointer

 
SCRATCHPTR 0x514

Pointer to data area used for temporary storage

 
MAXPACKETSIZE 0x518

Length of keystream generated when MODE.LENGTH = Extended

 
RATEOVERRIDE 0x51C

Data rate override setting.

 

TASKS_KSGEN

Address offset: 0x000

Start generation of keystream. This operation will stop by itself when completed.

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                               A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A W

TASKS_KSGEN

   

Start generation of keystream. This operation will stop by itself when completed.

     

Trigger

1

Trigger task

TASKS_CRYPT

Address offset: 0x004

Start encryption/decryption. This operation will stop by itself when completed.

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                               A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A W

TASKS_CRYPT

   

Start encryption/decryption. This operation will stop by itself when completed.

     

Trigger

1

Trigger task

TASKS_STOP

Address offset: 0x008

Stop encryption/decryption

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                               A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A W

TASKS_STOP

   

Stop encryption/decryption

     

Trigger

1

Trigger task

TASKS_RATEOVERRIDE

Address offset: 0x00C

Override DATARATE setting in MODE register with the contents of the RATEOVERRIDE register for any ongoing encryption/decryption

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                               A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A W

TASKS_RATEOVERRIDE

   

Override DATARATE setting in MODE register with the contents of the RATEOVERRIDE register for any ongoing encryption/decryption

     

Trigger

1

Trigger task

EVENTS_ENDKSGEN

Address offset: 0x100

Keystream generation complete

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                               A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A RW

EVENTS_ENDKSGEN

   

Keystream generation complete

     

NotGenerated

0

Event not generated

     

Generated

1

Event generated

EVENTS_ENDCRYPT

Address offset: 0x104

Encrypt/decrypt complete

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                               A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A RW

EVENTS_ENDCRYPT

   

Encrypt/decrypt complete

     

NotGenerated

0

Event not generated

     

Generated

1

Event generated

EVENTS_ERROR ( Deprecated )

Address offset: 0x108

CCM error event

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                               A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A RW

EVENTS_ERROR

   

CCM error event

Deprecated

     

NotGenerated

0

Event not generated

     

Generated

1

Event generated

SHORTS

Address offset: 0x200

Shortcuts between local events and tasks

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                               A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A RW

ENDKSGEN_CRYPT

   

Shortcut between event ENDKSGEN and task CRYPT

     

Disabled

0

Disable shortcut

     

Enabled

1

Enable shortcut

INTENSET

Address offset: 0x304

Enable interrupt

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                           C B A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A RW

ENDKSGEN

   

Write '1' to enable interrupt for event ENDKSGEN

     

Set

1

Enable

     

Disabled

0

Read: Disabled

     

Enabled

1

Read: Enabled

B RW

ENDCRYPT

   

Write '1' to enable interrupt for event ENDCRYPT

     

Set

1

Enable

     

Disabled

0

Read: Disabled

     

Enabled

1

Read: Enabled

C RW

ERROR

   

Write '1' to enable interrupt for event ERROR

Deprecated

     

Set

1

Enable

     

Disabled

0

Read: Disabled

     

Enabled

1

Read: Enabled

INTENCLR

Address offset: 0x308

Disable interrupt

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                           C B A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A RW

ENDKSGEN

   

Write '1' to disable interrupt for event ENDKSGEN

     

Clear

1

Disable

     

Disabled

0

Read: Disabled

     

Enabled

1

Read: Enabled

B RW

ENDCRYPT

   

Write '1' to disable interrupt for event ENDCRYPT

     

Clear

1

Disable

     

Disabled

0

Read: Disabled

     

Enabled

1

Read: Enabled

C RW

ERROR

   

Write '1' to disable interrupt for event ERROR

Deprecated

     

Clear

1

Disable

     

Disabled

0

Read: Disabled

     

Enabled

1

Read: Enabled

MICSTATUS

Address offset: 0x400

MIC check result

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                               A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A R

MICSTATUS

   

The result of the MIC check performed during the previous decryption operation

     

CheckFailed

0

MIC check failed

     

CheckPassed

1

MIC check passed

ENABLE

Address offset: 0x500

Enable

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                             A A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A RW

ENABLE

   

Enable or disable CCM

     

Disabled

0

Disable

     

Enabled

2

Enable

MODE

Address offset: 0x504

Operation mode

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID               C             B B                             A
Reset 0x00000001 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
ID Access Field Value ID Value Description
A RW

MODE

   

The mode of operation to be used. Settings in this register apply whenever either the KSGEN task or the CRYPT task is triggered.

     

Encryption

0

AES CCM packet encryption mode

     

Decryption

1

AES CCM packet decryption mode

B RW

DATARATE

   

Radio data rate that the CCM shall run synchronous with

     

1Mbit

0

1 Mbps

     

2Mbit

1

2 Mbps

     

125Kbps

2

125 kbps

     

500Kbps

3

500 kbps

C RW

LENGTH

   

Packet length configuration

     

Default

0

Default length. Effective length of LENGTH field in encrypted/decrypted packet is 5 bits. A keystream for packet payloads up to 27 bytes will be generated.

     

Extended

1

Extended length. Effective length of LENGTH field in encrypted/decrypted packet is 8 bits. A keystream for packet payloads up to MAXPACKETSIZE bytes will be generated.

CNFPTR

Address offset: 0x508

Pointer to data structure holding the AES key and the NONCE vector

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A RW

CNFPTR

   

Pointer to the data structure holding the AES key and the CCM NONCE vector (see table CCM data structure overview)

INPTR

Address offset: 0x50C

Input pointer

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A RW

INPTR

   

Input pointer

OUTPTR

Address offset: 0x510

Output pointer

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A RW

OUTPTR

   

Output pointer

SCRATCHPTR

Address offset: 0x514

Pointer to data area used for temporary storage

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A RW

SCRATCHPTR

   

Pointer to a scratch data area used for temporary storage during keystream generation, MIC generation and encryption/decryption.

The scratch area is used for temporary storage of data during keystream generation and encryption.

When MODE.LENGTH = Default, a space of 43 bytes is required for this temporary storage. When MODE.LENGTH = Extended, a space of (16 + MAXPACKETSIZE) bytes is required.

MAXPACKETSIZE

Address offset: 0x518

Length of keystream generated when MODE.LENGTH = Extended

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                 A A A A A A A A
Reset 0x000000FB 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 0 1 1
ID Access Field Value ID Value Description
A RW

MAXPACKETSIZE

 

[0x001B..0x00FB]

Length of keystream generated when MODE.LENGTH = Extended. This value must be greater than or equal to the subsequent packet payload to be encrypted/decrypted.

RATEOVERRIDE

Address offset: 0x51C

Data rate override setting.

Override value to be used instead of the setting of MODE.DATARATE. This override value applies when the RATEOVERRIDE task is triggered.

Bit number 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ID                                                             A A
Reset 0x00000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ID Access Field Value ID Value Description
A RW

RATEOVERRIDE

   

Data rate override setting

     

1Mbit

0

1 Mbps

     

2Mbit

1

2 Mbps

     

125Kbps

2

125 kbps

     

500Kbps

3

500 kbps

Electrical specification

Timing specification

Symbol Description Min. Typ. Max. Units
tkgen

Time needed for keystream generation (given priority access to destination RAM block)

50 µs