Building a list of available BLE devices

[Andreas]

Hello, I want to build a list of available BLE devices and show the device names to the user via a display (pretty normal BLE search). The search shall be done for devices with the same base uuid. I started with the example "ble_app_uart_c_S120". I was able to change the project, so that the search is done for the base UUID I want to. But now, the project direcly connects to the device that is found. Do I need to connect to a device, to get the the device name? The device name should be sent by the advertising packages. So a connection should not be needed!? Where can I get the advertising data after starting the search with "scan_start();"? Especially, if there are more than one device on-air with the same base uuid?

Thanks and best regards, BTprogrammer

PS: I am using nRF51822 with S120 softdevice of course, in central role.

[Edit:]

I found this tutorial here: central tutorial

Now I tried to read out the data from p_adv_report->data[i]. But I didn`t find the advertised device name. Is it stored in that data field?

[Andreas]

Ok, I think I got it... :-) The p_adv_report->data field must be parsed for the device name. I struggled with the position I did this. For me, the trick was to do it before the function is_uuid_present() is called. This function seems to change the data field. After this function call, the device name isn`t content of the data field. That is what it looks like for me... Maybe some Nordic expert can give a better explanation about that.

I wrote a quick and dirty device name parse function. Hope this code helps someone:

static bool parseDeviceName(const ble_uuid_t *p_target_uuid, 
                        const ble_gap_evt_adv_report_t *p_adv_report){
uint32_t index = 0;
uint8_t *p_data = (uint8_t *)p_adv_report->data;

while (index < p_adv_report->dlen)
{
    uint8_t field_length = p_data[index];
    uint8_t field_type   = p_data[index+1];
			if ( (field_type == BLE_GAP_AD_TYPE_SHORT_LOCAL_NAME)
								|| (field_type == BLE_GAP_AD_TYPE_COMPLETE_LOCAL_NAME)
								)
			{
					printf("length_1: %d\r", field_length);
					memcpy(deviceName, p_adv_report->data+2, field_length);
					deviceName[p_adv_report->data[0]] = 0x00;
					printf("Name: %s\r", deviceName);
					return true;
			}
			index += field_length + 1;
	}
return false;
}

"deviceName" is a global static char array. After calling the parseDeviceName() funtion, the received name is stored in that array and can be used.

Regards, BTprogrammer

[Hung Bui]

Hi,

Could you double check is_uuid_present() would modify the input p_adv_report ? You can simply add breakpoints before and after the call and check if it's modified. I don't think it is.

You can actually use the function adv_report_parse() in main.c in ble_app_hrs_c project to parse any field.

[Andreas]

Hi Hung, Thanks for your reply. adv_report_pars() is a cool function. But isnt part of the uart_c project. Therfor it wasnt in my scope... Thanks for that hint. I double checkt the content of p_adv_report->data field. And the device name isnt part of the data field after calling is_uuid_present(...). But it is the first part in the data field before calling is_uuid_present(...). At the moment I dont know where this happens. But the parsing for the device name only works when doing it befor calling is_uuid_present(...).

Regards, BTprogrammer

[Andreas]

Other question, is there a exisiting list of found devices from the stack or the device manager? Or do I have to implement my own list of available devices in the BLE_GAP_EVT_ADV_REPORT event? (Thats the task I am working on at the moment...)

[Andreas]

I had a closer look to the is_uuid_present() function. For me it does not make any sense why that bahaviour happens. I dont knwo if it matters, I am using SDK 10.0.0. I also checked for any changes to SDK 11.0.0 with WinMerge. But didnt find anything special.

[Hung Bui]

@BT: You can debug and step into the code and see when the data in p_adv_report changed. You can add p_adv_report to watchlist and can see the data, live, when you step.

There is no list of found device in device manager for central. You would need to create one on your own. We only store the list of bonded device.