Use BLE_GAP_EVT_ADV_REPORT to scan for beacon

[Max]

Setup:

Module: nRF51822.

SDK version:nRF5_SDK_11.0.0_89a8197.

Example: ble_app_uart.

Softdevice: S130.

I use ble_nus_string_send on the BLE_GAP_EVT_ADV_REPORT in on_ble_evt tring to scan for

beacon and found that it only outputs strings less than 20 bytes. Dig a little further, I found it's

because of

if (length > BLE_NUS_MAX_DATA_LEN)
{
return NRF_ERROR_INVALID_PARAM;
}

in ble_nus.c while BLE_NUS_MAX_DATA_LEN is defined as (GATT_MTU_SIZE_DEFAULT - 3) and

GATT_MTU_SIZE_DEFAULT is defined to be 23.

My question is how to modify so I can scan for beacon whose data length is about 30? Or it's just

not supported in S130 to scan for beacons this way?

[Hung Bui]

Hi Max, 
I assume you are using S130. 

Unfortunately larger ATT_MTU and longer Datalengh is not supported by S130. 

So if you want to send via notification more than 23 bytes, you need to segment the data send it in multiple packets. 

On S132 (for nRF52) it's supported up to 247 byte ATT_MTU that you can use to send notification. 

[Max]

Hi Bui,

Yes, I am using S130. The thing is that I am not trying to send beacon signals. Instead, I want to scan for it. is there a workaround in BLE_GAP_EVT_ADV_REPROT?

Also, I am targeting nrf51822 module and S132 is not applicable.

[Hung Bui]

Hi Max, 

Please explain why you call ble_nus_string_send() , what's it for ? 

So you want to see the beacon data on the phone ? correct ? 

[Max]

Yes, you can say that.

[Hung Bui]

Then please read my reply from the beginning. 
The way we send the data from the nRF52 to the phone is via notification. And there is a limitation of the notification compare to read/write. 

[Max]

My question is to scan for a specific beacon signal in nRF51. How to implement this in nRF51?

[Hung Bui]

Have you managed to scan for beacon ? 
You mentioned that you found if the beacon datasize is above 20 bytes you can't send it via ble_nus_string_send(). I assume that you have managed to scan for beacon with smaller than 20 bytes payload ? 
If you haven't implemented the code to scan, please look at the examples in ble_central folder. 

[Max]

The problem is how do I get the beacon data with more than 20 bytes in nRF51. Not sending, please.
In anther words, how to achieve the condition in BLE_GAP_EVT_ADV_REPORT events (line 336 of attached main.c)

if ((p_adv_report->dlen == 30 ) && (ble_state == BLE_CONNECTED) && ...

where p_adv_report->dlen could never be 30 due to S130 limitation.

[Hung Bui]

Are you sure it was because of :

if ((p_adv_report->dlen == 30 ) && (ble_state == BLE_CONNECTED)

How do you know if you receive the beacon advertising packet or not ? If you simply call ble_nus_string_send() when it matched then it will never send out the notification to the phone because the length is over 20 bytes. 

Please try to test again with just toggling a GPIO or printout the log. Also try to test with simple check for example only use "if ((p_adv_report->dlen == 30 )  " or just printout any advertising packet you receives.

As far as I know the nRF51 shouldn't have any trouble scanning for beacon having more than 20 bytes payload. 

[Max]

You're right. I wasn't thinking straight and misunderstood. Now I can wake up from BLE idle by a specific beacon signal. Thank you very much for the help.