Android studio Peripherals onCharacteristicWriteRequest

[HuanVH]

Hello

I am writing a peripheral emulator application on android.
My peripherals include 2 services and 4 characteristics. I tested my application with nRF Connect on the computer, it didn't get any errors.
My central device, works very well with a peripheral using nRF52832.
When I tried to connect the application and the central device, the connection was successful. I have enabled the notification flags. But I cannot write data from the central device to the application via any characteristic. I set the breakpoint in the onCharacteristicWriteRequest event, but without anything going on, the application still runs while I send data. With nRF Connect, the onCharacteristicWriteRequest event is still normal.
Please answer and give me solution, thanks

i'm using SDK 15.3, SoC: nRF52832, SD: 6.1.1 and Android 9

Central code:

Write data to characteristic

uint32_t ble_smk_info_write(ble_smk_t * p_smk, uint8_t * data, uint16_t length)
{
    VERIFY_PARAM_NOT_NULL(p_smk);
    if (p_smk->conn_handle == BLE_CONN_HANDLE_INVALID)
    {
        return NRF_ERROR_INVALID_STATE;
    }
    ble_gattc_write_params_t const write_params = {.write_op = BLE_GATT_OP_WRITE_CMD,
        .flags = BLE_GATT_EXEC_WRITE_FLAG_PREPARED_WRITE,
        .handle = p_smk->peer_info_db.char_handle,
        .offset = 0,
        .len = length,
        .p_value = data};
    return sd_ble_gattc_write(p_smk->conn_handle, &write_params);
}

Android code:

Setup service and characteristic 

        mCharKey = new BluetoothGattCharacteristic(VNET_CHAR_KEY, BluetoothGattCharacteristic.PROPERTY_NOTIFY, 1);
        BluetoothGattDescriptor descriptor = new BluetoothGattDescriptor(CLIENT_CHARACTERISTIC_CONFIGURATION_UUID,
                (BluetoothGattDescriptor.PERMISSION_READ | BluetoothGattDescriptor.PERMISSION_WRITE));
        descriptor.setValue(new byte[]{0, 0});
        mCharKey.addDescriptor(descriptor);

        mCharInfo = new BluetoothGattCharacteristic(VNET_CHAR_INFO,BluetoothGattCharacteristic.PROPERTY_WRITE, BluetoothGattCharacteristic.PERMISSION_WRITE);
        mCharInfo.setValue(new byte[] {0, 0, 0, 0, 0, 0, 0, 0, 0});

        mServiceKey = new BluetoothGattService(VNET_SERVICE_KEY, BluetoothGattService.SERVICE_TYPE_PRIMARY);
        mServiceKey.addCharacteristic(mCharKey);
        mServiceKey.addCharacteristic(mCharInfo);

        mCharCmd = new BluetoothGattCharacteristic(VNET_CHAR_CMD, BluetoothGattCharacteristic.PROPERTY_NOTIFY, 1);
        BluetoothGattDescriptor descriptor1 = new BluetoothGattDescriptor(CLIENT_CHARACTERISTIC_CONFIGURATION_UUID,
                (BluetoothGattDescriptor.PERMISSION_READ | BluetoothGattDescriptor.PERMISSION_WRITE));
        descriptor1.setValue(new byte[]{0, 0});
        mCharCmd.addDescriptor(descriptor1);

        mCharResp = new BluetoothGattCharacteristic(VNET_CHAR_RESP, BluetoothGattCharacteristic.PROPERTY_WRITE, BluetoothGattCharacteristic.PERMISSION_WRITE);
        mCharResp.setValue(new byte[] {0, 0, 0, 0, 0, 0, 0, 0, 0});

        mServicePhone = new BluetoothGattService(VNET_SERVICE_PHONE, BluetoothGattService.SERVICE_TYPE_PRIMARY);
        mServicePhone.addCharacteristic(mCharCmd);
        mServicePhone.addCharacteristic(mCharResp);

Callback

        @Override
        public void onCharacteristicWriteRequest(BluetoothDevice device, int requestId, BluetoothGattCharacteristic characteristic, boolean preparedWrite, boolean responseNeeded, int offset, byte[] value) {
            super.onCharacteristicWriteRequest(device, requestId, characteristic, preparedWrite, responseNeeded, offset, value);
            String s = "";
            for (byte vl: value) {
                s = String.format("%02X ", vl);
            }
            Log.v(TAG, "Char: " + characteristic.getUuid().toString() + " offset " + offset + " Value " + s);

            if(tmp == mCurrentServiceFragment.getCharacteristicUUID().get(1))
            {
            
            }
            mGattServer.sendResponse(device, requestId, BluetoothGatt.GATT_SUCCESS, 0, null);
        }

[Edvin]

Hello,

So your peripheral works when you test it against nRF Connect, but not on the central.

Can you see what your ble_smk_info_write() function returns? What does sd_ble_gattc_write() return?

Best regards,

Edvin

[HuanVH]

I send the data right away at the db_disc handler function, after running the ble_smk_on_db_disc_evt function. I think that's the problem, I put a breakpoint at the send function, the conn_handle are all available.
This only happens with peripherals running on Android, with peripherals running on SoCs do not have this problem. I am forced to use 1 app_timer to send this data.
So is there a best way to identify all services and characteristics that have been discovered?
Thanks a lot

[Edvin]

Look at how this is done in the central examples in the SDK. 

Look for the discovery complete  event inside the discovery handler, and ensure that the specific characteristic is discovered before you use it. 

So what did sd_ble_gattc_write() return?

[HuanVH]

sd_ble_gattc_write() return success

Thanks for helping