AAR — Accelerated address resolver

Accelerated address resolver is a cryptographic support function for implementing the "Resolvable Private Address Resolution Procedure" described in the Bluetooth Core specification v4.0. "Resolvable private address generation" should be achieved using ECB and is not supported by AAR.

The procedure allows two devices that share a secret key to generate and resolve a hash based on their device address. The AAR block enables real-time address resolution on incoming packets when configured as described in this chapter. This allows real-time packet filtering (whitelisting) using a list of known shared keys (Identity Resolving Keys (IRK) in Bluetooth).

Shared resources

The AAR shares registers and other resources with the peripherals that have the same ID as the AAR. The user must therefore disable all peripherals that have the same ID as the AAR before the AAR can be configured and used.

Disabling a peripheral that have the same ID as the AAR will not reset any of the registers that are shared with the AAR. It is therefore important to configure all relevant AAR registers explicitly to secure that it operates correctly.

See the Instantiation table in Instantiation for details on peripherals and their IDs.

EasyDMA

The AAR implements EasyDMA for reading and writing to the RAM. The EasyDMA will have finished accessing the RAM when the END, RESOLVED, and NOTRESOLVED events are generated.

If the IRKPTR, ADDRPTR and the SCRATCHPTR is 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.

Resolving a resolvable address

As per Bluetooth specification, a private resolvable address is composed of six bytes.

Figure 1. Resolvable address

To resolve an address the ADDRPTR register must point to the start of packet. The resolver is started by triggering the START task. A RESOLVED event is generated when the AAR manages to resolve the address using one of the Identity Resolving Keys (IRK) found in the IRK data structure. The AAR will use the IRK specified in the register IRK0 to IRK15 starting from IRK0. How many to be used is specified by the NIRK register. The AAR module will generate a NOTRESOLVED event if it is not able to resolve the address using the specified list of IRKs.

The AAR will go through the list of available IRKs in the IRK data structure and for each IRK try to resolve the address according to the Resolvable Private Address Resolution Procedure described in the Bluetooth Specification1. The time it takes to resolve an address may vary depending on where in the list the resolvable address is located. The resolution time will also be affected by RAM accesses performed by other peripherals and the CPU. See the Electrical specifications for more information about resolution time.

The AAR will only do a comparison of the received address to those programmed in the module. And not check what type of address it actually is.

The AAR will stop as soon as it has managed to resolve the address, or after trying to resolve the address using NIRK number of IRKs from the IRK data structure. The AAR will generate an END event after it has stopped.

Figure 2. Address resolution with packet preloaded into RAM

Use case example for chaining RADIO packet reception with address resolution using AAR

The AAR may be started as soon as the 6 bytes required by the AAR have been received by the RADIO and stored in RAM. The ADDRPTR pointer must point to the start of packet.

Figure 3. Address resolution with packet loaded into RAM by the RADIO

IRK data structure

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

Table 1. IRK data structure overview
Property Address offset Description
IRK0 0 IRK number 0 (16 - byte)
IRK1 16 IRK number 1 (16 - byte)
.. .. ..
IRK15 240 IRK number 15 (16 - byte)

Registers

Table 2. Instances
Base address Peripheral Instance Description Configuration
0x4000F000 AAR AAR

Acelerated Address Resolver

    
Table 3. Register Overview
Register Offset Description
TASKS_START 0x000

Start resolving addresses based on IRKs specified in the IRK data structure

  
TASKS_STOP 0x008

Stop resolving addresses

  
EVENTS_END 0x100

Address resolution procedure complete

  
EVENTS_RESOLVED 0x104

Address resolved

  
EVENTS_NOTRESOLVED 0x108

Address not resolved

  
INTENSET 0x304

Enable interrupt

  
INTENCLR 0x308

Disable interrupt

  
STATUS 0x400

Resolution status

  
ENABLE 0x500

Enable AAR

  
NIRK 0x504

Number of IRKs

  
IRKPTR 0x508

Pointer to IRK data structure

  
ADDRPTR 0x510

Pointer to the resolvable address

  
SCRATCHPTR 0x514

Pointer to data area used for temporary storage

  

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 RW Field Value Id Value Description
A RW

END

    

Write '1' to Enable interrupt for END event

See EVENTS_END

     

Set

1

Enable

     

Disabled

0

Read: Disabled

     

Enabled

1

Read: Enabled

B RW

RESOLVED

    

Write '1' to Enable interrupt for RESOLVED event

See EVENTS_RESOLVED

     

Set

1

Enable

     

Disabled

0

Read: Disabled

     

Enabled

1

Read: Enabled

C RW

NOTRESOLVED

    

Write '1' to Enable interrupt for NOTRESOLVED event

See EVENTS_NOTRESOLVED

     

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 RW Field Value Id Value Description
A RW

END

    

Write '1' to Disable interrupt for END event

See EVENTS_END

     

Clear

1

Disable

     

Disabled

0

Read: Disabled

     

Enabled

1

Read: Enabled

B RW

RESOLVED

    

Write '1' to Disable interrupt for RESOLVED event

See EVENTS_RESOLVED

     

Clear

1

Disable

     

Disabled

0

Read: Disabled

     

Enabled

1

Read: Enabled

C RW

NOTRESOLVED

    

Write '1' to Disable interrupt for NOTRESOLVED event

See EVENTS_NOTRESOLVED

     

Clear

1

Disable

     

Disabled

0

Read: Disabled

     

Enabled

1

Read: Enabled

 

STATUS

Address offset: 0x400

Resolution status

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
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 RW Field Value Id Value Description
A R

STATUS

  

[0..15]

The IRK that was used last time an address was resolved

 

ENABLE

Address offset: 0x500

Enable AAR

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 RW Field Value Id Value Description
A RW

ENABLE

    

Enable or disable AAR

     

Disabled

0

Disable

     

Enabled

3

Enable

 

NIRK

Address offset: 0x504

Number of IRKs

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
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 RW Field Value Id Value Description
A RW

NIRK

  

[1..16]

Number of Identity root keys available in the IRK data structure

 

IRKPTR

Address offset: 0x508

Pointer to IRK data structure

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 RW Field Value Id Value Description
A RW

IRKPTR

    

Pointer to the IRK data structure

 

ADDRPTR

Address offset: 0x510

Pointer to the resolvable address

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 RW Field Value Id Value Description
A RW

ADDRPTR

    

Pointer to the resolvable address (6-bytes)

 

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 RW Field Value Id Value Description
A RW

SCRATCHPTR

    

Pointer to a scratch data area used for temporary storage during resolution.A space of minimum 3 bytes must be reserved.

 

Electrical specification

AAR Electrical Specification

Symbol Description Min. Typ. Max. Units
tAAR,8

Time for address resolution of 8 IRKs

 48 µs
1 Bluetooth Specification Version 4.0 [Vol 3] chapter 10.8.2.3.
Documentation feedback | Developer Zone | Updated 2021-11-08