Connection to Android isn't stable

[Jeremy Hubbard]

I'm having an issue with maintaining a stable connection with the master control panel on an android device. Using the PCA10000 I am able to get a stable connection with a computer and transmit data, but when I move to an android device it isn't stable.

I started with the example project "nrf51-ble-app-lbs-throughput-test-5.1.0" and instead of continuously transmitting on a button event, I added a timer which triggers every 30ms to transmit 9 bytes acquired from an I2C sensor. It continues to do this until the button is pressed again.

On the android device I can connect to it, but as soon as I press the button to start sending data the connection is lost and the error returned from the transmit function, ble_lbs_data_send(), is 0x3401.

I am using the nRF51822 development kit with the SoftDevice s110, Keilv5 evaluation version. I have also stopped the sensors from measuring and am transmitting dummy data, which doesn't change the error at all.

Thanks, Jeremy

[Ole Morten]

You can read about the 0x3401 error in this question.

If you're working with TWI sensors, could it be that you have not fixed your TWI module to be softdevice compatible? If so, you'll see HardFaults when if the module tries to access the softdevice directly, but this should be fairly easy to see with a debugger, by letting the chip run freely and then halt when the connection is lost. You may have use in taking a look at this question, and this GitHub example, the latter if you're using a second revision chip (FA or later for QFN).

[Jeremy Hubbard]

I have already updated the TWI driver to be softdevice compatible and I can transmit to a computer just fine. I'm not seeing hard faults.

Based on the 0x3401 error thread, I modified the error checking after the ble_lbs_data_send() command to:

err_code = ble_lbs_data_send(&m_lbs, data);
if (err_code != BLE_ERROR_GATTS_SYS_ATTR_MISSING 
        && err_code != NRF_SUCCESS 
        && err_code != BLE_ERROR_INVALID_CONN_HANDLE 
        && err_code != NRF_ERROR_INVALID_STATE 
        && err_code != BLE_ERROR_NO_TX_BUFFERS)
{
    APP_ERROR_CHECK(err_code);
}

and now I can transmit data, but after the connection is established with the Android device it disconnects every 16.5 seconds, like clockwork. Any ideas?

Thanks, Jeremy

[Ole Morten]

Have you tried using the sniffer to see what happens on-air? https://www.nordicsemi.com/eng/content/download/39099/660783/file/ble-sniffer_win_0.9.5.zip

Also, what is the reason when you get the DISCONNECTED event on the nRF51 side? You should also check that it isn't a connection parameter update that's failing, i.e. that you're asking for parameters that the Android device doesn't accept. If so, you'll see on_conn_params_evt() being called with evt_type BLE_CONN_PARAMS_EVT_FAILED. Do you see this when running with a debugger?

[Jeremy Hubbard]

It looks like the error thrown as seen using the sniffer is Error code: Unacceptable Connection Interval (0x3b). I am seeing that the error event BLE_CONN_PARAMS_EVT_FAILED being called in the debugger. I am using the Android Master Control Panel app when I see this error. I am only sending notifications in my program in the nRF51822, what could be causing that error?

Thanks, Jeremy

[Ole Morten]

Take a look at this question: https://devzone.nordicsemi.com/index.php/what-is-connection-parameters

If the Central for some reason rejects the parameters you request, you will get this error back. To fix it, you must therefore try to request other parameters.

However, I think my first reply answered the original question, so to clear up this question, I'd be happy if you could click the "Accept as answer" button below it. If you have any further problems, I suggest you post them separately, to keep each question here as focused as possible.