Limitations of Scan Parameters in Coded PHY

[Genyu]

Hello, Nordic!

When a scan is started with certain scan parameters, a timeout event (NRF_BLE_SCAN_EVT_SCAN_TIMEOUT) will occur in a time less than the specified timeout value.

When scanning with Scan Parameters (OK), a timeout event occurs after 10 seconds as expected.

However, When scanning with Scan Parameters (NG), the timeout event occurs immediately after the scan starts.

When using Coded PHY, is there a limit to the scan interval or scan window?

・Scan Parameters（OK）

static ble_gap_scan_params_t const m_scan_param =
{
    .extended      = 0x01,
    .active        = 0x01,
    .interval      = 160,
    .window        = 80,
    .filter_policy = BLE_GAP_SCAN_FP_ACCEPT_ALL,
    .timeout       = 1000,
    .scan_phys     = BLE_GAP_PHY_CODED,
};

・Scan Parameters（NG）

static ble_gap_scan_params_t const m_scan_param =
{
    .extended      = 0x01,
    .active        = 0x01,
    .interval      = 4,
    .window        = 4,
    .filter_policy = BLE_GAP_SCAN_FP_ACCEPT_ALL,
    .timeout       = 1000,
    .scan_phys     = BLE_GAP_PHY_CODED,
};

Test Environment

• SDK：17.0.2
• SD：s140_nrf52_7.2.0
• DK：PCA10056（v2.0.0）
• Project：nRF5_SDK_17.0.2_d674dde\examples\ble_central\ble_app_hrs_c

Thanks

 

[haakonsh]

The Interval and Window scan parameters are too short. Note that their value is in units of 0.625ms and Coded PHY needs 8 times longer Windows and Intervals than 1mbps PHY. 

[Genyu]

Thank you for your help.

Does that mean that the scan parameters in Coded PHY should be in the following range?

・Scan Interval：0x0020 ~ 0xFFFF (20 ms ~ 40,959.375 s)
・Scan Window：0x0020 ~ 0xFFFF (20 ms ~ 40,959.375 s)

[haakonsh]

I would try out both the of those minimums and maximums, but I think those values are reasonable. 

[Genyu]

Thanks for trying!

I think sd_ble_gap_scan_start() should return an error if it is given scan parameters that do not work properly.

[haakonsh]

I agree completely, I think the devs have overlooked this issue. I'll have a chat with them, but given that the nRF5_sdk is in maintenance mode, I think it's unlikely that it will be fixed anytime soon. 

Did you find some parameters that works for you?