Is it possible to BLE scanning in one channel instead of 3 channel?

[Alan Ajit]

Dear nordic,

BLE advertising happens in 3 channel(37,38,39) and scanner scans these channel based on scan interval consecutively

I want to scan single channel instead of scanning 3 channels consecutively . Is it possible to scan one channel?

can you help me to solve this?

[Einar Thorsrud]

Hi,

You can scan on only one channel by setting the channel_mask field in the ble_gap_scan_params_t struct that you pass to the call to sd_ble_gap_scan_start().

[Alan Ajit]

Thanks for your replay but when i check the  ble_gap_scan_params_t  i can't find channel mask i am using central peripheral example in BLE how i change scanning in one channel only

[Einar Thorsrud]

Which SDK and SoftDevice version are you using? The ability to scan on specific channels was added in version SoftDevice version 6.0.0, which is used in SDK 15.0.0. It is not supported if you use an older SoftDevice.

[Alan Ajit]

Thanks i see channel mask in SDK 15.0.0 . 

channel mask has 40 bits that is 5 byte LSB for channel index 0 and MSB for channel index 39 if i set channel mask MSB to 0 and next 2 bits set to 1 scanning happens in channel 39 only is it right procedure for scanning one channel?

[Einar Thorsrud]

You can do like this (modified from this post):

/** @brief Parameters used when scanning. */
static ble_gap_scan_params_t const m_scan_params =
{
    .active             = 1,
    .interval           = SCAN_INTERVAL,
    .window             = SCAN_WINDOW,
    .timeout            = SCAN_DURATION,
    .scan_phys          = BLE_GAP_PHY_1MBPS,
    .filter_policy      = BLE_GAP_SCAN_FP_ACCEPT_ALL,
    .channel_mask[4]    = 0x60, // <- DON'T SCAN ON CHANNEL 37 or 38
};

[Alan Ajit]

Sorry for late reply

I tested as per above modification 

For testing i use two nrf device one as Scanner and other as Advertiser

Scanner:-

static ble_gap_scan_params_t const m_scan_params =
{
.active = 1,
.interval = SCAN_INTERVAL,
.window = SCAN_WINDOW,
.timeout = SCAN_DURATION,
.scan_phys = BLE_GAP_PHY_1MBPS,
.filter_policy = BLE_GAP_SCAN_FP_ACCEPT_ALL,
.channel_mask[4] = 0x60, // <- DON'T SCAN ON CHANNEL 37 or 38
};

Advertiser:- modified in advertising_init(void)

ble_gap_adv_params_t m_adv_params;

m_adv_params.channel_mask[4] =0x80;

modified for Advertising in Channel's 37 and 38 advertising

But i get Advertising in Scanner(scanning only in 39 channel) how its possible?

Is it any mistake in my procedure?

[Einar Thorsrud]

That's odd. What do you do with m_scan_params m_adv_params after setting the channel mask_field? Can you upload the full source code for the advertise and scanner?

[Alan Ajit]

I tested Central peripheral example in SDk 15 

I am just modified  in scanner side

static ble_gap_scan_params_t const m_scan_params =
{
.active = 1,
.interval = SCAN_INTERVAL,
.window = SCAN_WINDOW,
.timeout = SCAN_DURATION,
.scan_phys = BLE_GAP_PHY_1MBPS,
.filter_policy = BLE_GAP_SCAN_FP_ACCEPT_ALL,
.channel_mask[4] = 0x60, // <- DON'T SCAN ON CHANNEL 37 or 38
};

and modified in advertiser side in advertising_init(void)

ble_gap_adv_params_t m_adv_params;

m_adv_params.channel_mask[4] =0x80;

just two things modified nothing more

[Einar Thorsrud]

 I still find it a bit strange. Can you show me your complete advertising_init() function?

[Alan Ajit]

This is my function 

/**@brief Function for initializing the Advertising functionality.
*/
static void advertising_init(void)
{
ret_code_t err_code;
ble_advertising_init_t init;
ble_gap_adv_params_t m_adv_params;
m_adv_params.channel_mask[4] =0x80;
memset(&init, 0, sizeof(init));

init.advdata.name_type = BLE_ADVDATA_FULL_NAME;
init.advdata.include_appearance = true;
init.advdata.flags = BLE_GAP_ADV_FLAGS_LE_ONLY_GENERAL_DISC_MODE;
init.advdata.uuids_complete.uuid_cnt = sizeof(m_adv_uuids) / sizeof(m_adv_uuids[0]);
init.advdata.uuids_complete.p_uuids = m_adv_uuids;

init.config.ble_adv_fast_enabled = true;
init.config.ble_adv_fast_interval = APP_ADV_INTERVAL;
init.config.ble_adv_fast_timeout = APP_ADV_DURATION;
init.evt_handler = on_adv_evt;
// m_adv_params.channel_mask[4] =0x80;

err_code = ble_advertising_init(&m_advertising, &init);
APP_ERROR_CHECK(err_code);

ble_advertising_conn_cfg_tag_set(&m_advertising, APP_BLE_CONN_CFG_TAG);
}

nothing do additional . is it any wrong?

[Einar Thorsrud]

Yes, something's clearly wrong. You make instance of m_adv_params in your advertising_init() function where you set the channel_mask, but you never actually use this variable anywhere. It cannot have any effect whatsoever, so just remove it.

As you use the advertising module, you need to look at the first parameter of your call to ble_advertising_start(), the which is an instance of ble_advertising_t. This is called m_advertising in most examples. You should instead set something like this in your code before you call ble_advertising_init():

m_advertising.adv_params.channel_mask[4] = 0x80;

[Alan Ajit]

Thank you for your support.