NRF52811-QCAA-R7 datasheet(77/444 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 82, ADDRPTR on page 82, and the SCRATCHPTR on page 82 is not

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

Memory on page 16 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 register ADDRPTR on page 82 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 on page 81

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.

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