NRF52820-QDAA-R7 datasheet(88/437 Pages) NORDIC

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Peripherals

6.2 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).

6.2.1 EasyDMA

AAR implements EasyDMA for reading and writing to RAM. EasyDMA will have finished accessing RAM

when the END, RESOLVED, and NOTRESOLVED events are generated.

If the IRKPTR on page 93, ADDRPTR on page 93, and the SCRATCHPTR on page 93 is not

pointing to the Data RAM region, an EasyDMA transfer may result in a HardFault or RAM corruption. See

Memory on page 15 for more information about the different memory regions.

6.2.2 Resolving a resolvable address

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

random

LSB

MSB

1 0

hash

(24-bit)

prand

(24-bit)

Figure 25: Resolvable address

To resolve an address the register ADDRPTR on page 93 must point to the start of the packet. The

resolver is started by triggering the START task. A RESOLVED event is generated when AAR manages to

resolve the address using one of the Identity Resolving Keys (IRK) found in the IRK data structure. AAR will

use the IRK specified in the register IRK0 to IRK15 starting from IRK0. The register NIRK on page 92

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.

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.

AAR only compares the received address to those programmed in the module without checking the

address type.

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. AAR will generate an END event after it has stopped.

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NRF52820-QDAA-R7 Datasheet(PDF) 88 Page - Nordic Semiconductor

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