Setting resolvable private address

[Amit Chahar]

I want to set the resolvable private address ( RPA ) manually instead of letting softdevice do it. I went through documentation but I am not sure about it. I know that I can configure IRK and refresh interval in softdevice but I want to do it with my code to analyze the performance or to use own encryption method.

I am using this to set the RPA :

ble_gap_addr_t new_add ;
new_add.addr_type=BLE_GAP_ADDR_TYPE_RANDOM_PRIVATE_RESOLVABLE;
for(uint32_t j = 0; j < BLE_GAP_ADDR_LEN; j++){  
	new_add.addr[j] = rpa[j];
}
err_code = sd_ble_gap_address_set(BLE_GAP_ADDR_CYCLE_MODE_NONE, &new_add);
APP_ERROR_CHECK(err_code);

where "rpa" is generated by me using my own IRK.

But as mentioned in the sd_ble_gap_address_set() documentation :

If the address cycle mode is BLE_GAP_ADDR_CYCLE_MODE_NONE and the application is using privacy, the application must take care to generate and set new private addresses periodically to comply with the Privacy specification in Bluetooth Core Spec.

So, my doubts are :

1. I am able to set the RPA by using the above code and see it on the scanner but Is it the correct and valid way ? Are there any other options (eg. privacy) that needs to be set ? (Valid in the sense that other devices should be able to resolve it if they have correct IRK).

2. What is the minimum interval to refresh the RPA ?

Thanks in advance

[Ole Bauck]

Hi,

1. This is the correct and valid way.
2. The recommended for updating the address is 15 minutes as specified in the Bluetooth core specification 4.2 Vol 6 Part B Chapter 6.1:

6.1 PRIVATE ADDRESS GENERATION INTERVAL

A private address shall be generated using the Resolvable Private Address Generation (see Section 1.3.2.2).

The Link Layer shall set a timer determined by the Host. A new private address shall be generated when the timer expires. If the Link Layer is reset, a new private address shall be generated and the timer started with any value in the allowed range.

Note: If the private address is generated frequently, connection establishment times may be affected. It is recommended to set the timer to 15 minutes.

This can also be found in the SDK: BLE_GAP_DEFAULT_PRIVATE_ADDR_CYCLE_INTERVAL_S

[Amit Chahar]

So, RPA refresh has to be done in my code using timer ? There is nothing compulsory to set in softdevice for it? Is there any minimum interval (beside the recommended) to refresh the RPA?

[Ole Bauck]

To update the RPA every 15 minutes you have to use a timer, for example the app_timer module. There is no min or max interval (that I found at least), only the recommended.