NRF52810-QCAA-R datasheet(97/483 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

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 on page 101, ADDRPTR on page 101 and the SCRATCHPTR on page 101 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 22: Resolvable address

To resolve an address the ADDRPTR on page 101 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

Specification13. 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.

13 Bluetooth Specification Version 4.0 [Vol 3] chapter 10.8.2.3.

4430_161 v1.0

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