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).

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

A private resolvable address composed of 6 bytes.

To resolve an address the register ADDRPTR must point to the start of the 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. The register NIRK specifies how many IRKs should be used. 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 Core specification v4.0 [Vol 3] chapter 10.8.2.3. The time it takes to resolve an address varies due to the location in the list of the resolvable address. 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 only compares the received address to those programmed in the module without checking the address type.

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 IRKPTR 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	Accelerated 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

TASKS_START

Address offset: 0x000

Start resolving addresses based on IRKs specified in the 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
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_START										Start resolving addresses based on IRKs specified in the IRK data structure
			Trigger	1								Trigger task

TASKS_STOP

Address offset: 0x008

Stop resolving addresses

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 resolving addresses
			Trigger	1								Trigger task

EVENTS_END

Address offset: 0x100

Address resolution procedure 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_END										Address resolution procedure complete
			NotGenerated	0								Event not generated
			Generated	1								Event generated

EVENTS_RESOLVED

Address offset: 0x104

Address resolved

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_RESOLVED										Address resolved
			NotGenerated	0								Event not generated
			Generated	1								Event generated

EVENTS_NOTRESOLVED

Address offset: 0x108

Address not resolved

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_NOTRESOLVED										Address not resolved
			NotGenerated	0								Event not generated
			Generated	1								Event generated

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	END										Write '1' to enable interrupt for event END
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
B	RW	RESOLVED										Write '1' to enable interrupt for event RESOLVED
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
C	RW	NOTRESOLVED										Write '1' to enable interrupt for event 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	Access	Field	Value ID	Value								Description
A	RW	END										Write '1' to disable interrupt for event END
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
B	RW	RESOLVED										Write '1' to disable interrupt for event RESOLVED
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
C	RW	NOTRESOLVED										Write '1' to disable interrupt for event 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	Access	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	Access	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	Access	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	Access	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	Access	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	Access	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
t_AAR	Address resolution time per IRK. Total time for several IRKs is given as (1 µs + n * t_AAR), where n is the number of IRKs. (Given priority to the actual destination RAM block).				..	..	..	µs
t_AAR,8	Time for address resolution of 8 IRKs. (Given priority to the actual destination RAM block).					48		µs