Connection Loss between nRF and Iphone

[Mehdi]

Hi Nordic,

I'm using nRF51, SDK 12 and softdevice version S130 to stream data from nrf51 to iphone6 over BLE.

Sometimes, Few hours after launching streaming, the BLE communication between iphone and nrf51 is get lost.

Following the sniffing trace, the loss of connection was generated beacause nRF51 didn't respond to the connection event generated by smartphone.

nRF51 stream data using the code bellow :

memset(&params, 0, sizeof(params));
params.type = BLE_GATT_HVX_NOTIFICATION;
params.handle = p_translinks->rx_char_handles.value_handle;
params.p_data = data;
params.p_len = &length;

err_code  = sd_ble_gatts_hvx(p_translinks->conn_handle, &params);
if (err_code != NRF_SUCCESS &&
err_code != BLE_ERROR_INVALID_CONN_HANDLE &&
err_code != NRF_ERROR_INVALID_STATE &&
err_code != BLE_ERROR_NO_TX_PACKETS &&
err_code != NRF_ERROR_BUSY)
{
  APP_ERROR_CHECK(err_code);
}

When testing our work in another place this issue appears in a systematic way.

Could someone please can explain to me the cause of this issue

Best Regards,

Mehdi.

[David Edwin]

Requested actions:

1. Can you post the sniffer traces 

2. Can you state the 32 KHz clock source (Crystal or RC) and its accuracy (in ppm) on the nRF51 board

3. Can you state markings on top of your IC

4. I will look for the Sleep clock accuracy of the iPhone in the sniffer trace, which should be in the connect request. Please make sure that the connect request is present in the trace.

[Mehdi]

Hi David,

Thank you for your quick reply.

• the sniffer trace is bellow : 

            https://drive.google.com/file/d/1O8jS2S8YYREXJKIeDp3VmbPKmbHzRfdl/view?usp=sharing.

• The markings on the top of my IC is : ISP130301  BL 1625C.
• Clock source Crystal, i don't find clock occuracy on SDK_Config, so may be it's the default value.

Best Regards.

[David Edwin]

Can you attach the sniffer traces here here, you can also make the case private if desired.

I looked at the data sheet for the ISP130301 and I could not figure out the accuracy of the 32 KHz crystal used in the ISP130301. Please reach out to the manufacturer and get the accuracy of the 32 KHZ crystal.

Update the 

ble_stack_init()

function in SDK 12.x to set the crystal accuracy as stated by the manufacturer of the nRF51 module as the default used may not be correct.

[Mehdi]

Hi David, 

The occuracy i used is 20 PPM .

Please find attached the sniffer traces 

Best Regards

snifing streaming.pcapng

[David Edwin]

Comments:

1. The timeout seems to be 720 ms, which should be ok as it gives more than 20 missed packets before the link drops due to supervision timeout. (at a connection interval of 30ms)

2. The accuracy used in the code is 20ppm but this needs to match the actual accuracy of the 32 KHz crystal as used by the manufacturer. The SDK code is intended to set the 32 KHz accuracy as it is on the board. If the number used in this case i.e. 20ppm is incorrect you will get link losses.

Actions on your end:

- Get the 32 KHz crystal accuracy from your manufacturer or from the datasheets of the module

- Change the crystal drift to a higher level perhaps 50ppm or more and verify if the stability increases

- You can also change the 32KHz source to the internal 32KHz RC source so you are not dependent on the module vendor's 32 KHz clock source. Verify if the stability increases.

[Mehdi]

Hi David,

I think you talk about this table. Right ?

 

Best Regards

[MartinBL]

That seems to be it. It looks like the crystal has a +-40 ppm accuracy, so you should try to use that in your code rather than 20. As David mentions, you can also try to use even higher PPMs or the internal RC source to rule out any issues with your external crystal.