About scan timeout

[June6]

Hi,

I am using SDK 17.1.0 as a host scanner. When I changed the timeout to 0, there was a problem with the connection slave (NRF_ERROR_INVALID_PARAM). I'm pretty sure the problem is not caused by other conditions. Because other parameters remain the default. So when I want the scan to never time out, can I only restart the scan after the timeout?

[June6]

Oh! I see. The scan timeout parameter is NRF_ BLE_ SCAN_ SCAN_ DURATION. Not NRF_BLE_SCAN_SUPERVISION_TIMEOUT. 

But why is it wrong to change this parameter from 4000 to 0?

[Einarh]

Hello!

According to the documentation, NRF_BLE_SCAN_SCAN_DURATION can be set to 0x0000 to continue indefinitely:

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fsdk_nrf5_v17.1.0%2Fgroup__nrf__ble__scan__config.html&cp=8_1_6_2_15_0_9&anchor=gacdb9b51bb850e2dcb8b07baa78d45402

But have you made sure all your scanning parameters are compatible with each other?

You might have to change some of the other default parameters before you can remove the scan timeout.

Best regards,

Einar

[Einarh]

So it looks like sd_ble_ gap_connect() is complaining about something in your ble_gap_scan_params_t struct.

I assume what you are trying to do is set the ble_gap_scan_params_t::timeout value to zero?

According to the documentation it seems like setting it to zero should be equivalent to an unlimited timeout, so I'm not sure why this would cause an error.

Have you tried printing the contents of the scan params struct to check if it looks like you'd expect?

[June6]

I haven't confirmed it, but in my own program, other conditions remain unchanged. Changing the value of the timeout parameter to 0 will cause this error code.

I don't understand this very much, so I did it again in the official sample code uart_c.

The results obtained are still as above.

Incidentally, some scanning and filtering conditions are added, which can be connected normally. Until the timeout parameter is changed to 0.

[June6]

The following are all parameters related to the scanning part:

#define NRF_BLE_SCAN_SCAN_INTERVAL 160

#define NRF_BLE_SCAN_SCAN_DURATION 0

#define NRF_BLE_SCAN_SCAN_WINDOW 80

#define NRF_BLE_SCAN_MIN_CONNECTION_INTERVAL 7.5

#define NRF_BLE_SCAN_MAX_CONNECTION_INTERVAL 30

#define NRF_BLE_SCAN_SLAVE_LATENCY 0

#define NRF_BLE_SCAN_SUPERVISION_TIMEOUT 4000 // 0

#define NRF_BLE_SCAN_SCAN_PHY 1

If the timeout parameter is set to 0, will other parameters conflict? Or is the connection error because the slave does not accept this value?

[Einarh]

Looking more into this I found this post, giving some context to how the supervision timeout is intended to be used:

https://devzone.nordicsemi.com/f/nordic-q-a/10636/what-are-latency-and-supervision-timeout-limits

With this in mind, I believe your best option might be to set a high value for the supervision timeout and restart the scan when it times out.

My understanding is that the supervision timeout is how long you will allow to keep a connection while no packets have been sent, so it makes sense if this value is not allowed to be 0.

[June6]

okay, thank you. I'll mend the basics.