For a custom BLE service, write operation doesn't seem to work

RE: For a custom BLE service, write operation doesn't seem to work

cbd — Thu, 19 Sep 2019 11:25:03 GMT

Okay. I was just about to have a closer look.

I'm glad that you've sorted it.

RE: For a custom BLE service, write operation doesn't seem to work

tinytrex — Wed, 18 Sep 2019 18:50:54 GMT

Never-mind. This worked after changing the permissions of the relay service characteristics in the peripheral.

RE: For a custom BLE service, write operation doesn't seem to work

tinytrex — Wed, 18 Sep 2019 14:13:35 GMT

Yes. Notifications are enabled on both the central and peripheral. But notifications itself aren't the issue. It's the 'write' that is not getting to the peripheral.

RE: For a custom BLE service, write operation doesn't seem to work

cbd — Wed, 18 Sep 2019 13:53:14 GMT

That's a lot of code to check through.

Are you relying on a notification trigger in your peripheral to detect when the characteristic has been updated or are you polling it?

This is the code from my current nRF52840 based project for updating and triggering a notification, I've only included the important bits:

    ble_gatts_hvx_params_t params;

    memset(&params, 0, sizeof(params));
    params.type = BLE_GATT_HVX_NOTIFICATION;
    params.p_len = &len;

    /* update and notify for the characteristic */
    params.handle = m_LiveDriveService.lds_char_result_handles.value_handle;
    params.p_data = m_scratch_buffer;

    err_code = sd_ble_gatts_hvx(m_LiveDriveService.conn_handle, &params);
    if (NRF_SUCCESS != err_code)
    { /* notifications may not be enabled, attempt to update data */
        ble_gatts_value_t valueData;
        valueData.len = len;
        valueData.offset = 0;
        valueData.p_value = m_scratch_buffer;
        NRF_LOG_HEXDUMP_DEBUG(m_scratch_buffer, len);
        err_code = sd_ble_gatts_value_set(m_LiveDriveService.conn_handle,
                                          m_LiveDriveService.lds_char_result_handles.value_handle,
                                          &valueData);
        if (NRF_SUCCESS != err_code)
        {
            return err_code;
        }
    }

Oh I forgot to mention both devices central and peripheral must enable notification on any characteristic that they wish to receive a notification even for.

RE: For a custom BLE service, write operation doesn't seem to work

tinytrex — Wed, 18 Sep 2019 13:44:19 GMT

Please note that the .write_op of the write_params is BLE_GATT_OP_WRITE_REQ and not BLE_GATT_OP_PREP_WRITE_REQ as mentioned in the relay_client.c source. I modified it just to test and forgot to revert before posting this.