Stopping the nRF52832 uart sample.

[mamorudeta]

Hi,

If the app keeps sending data at a certain rate, the numbers will skip and the software will stop.

I tried to see how much data I could communicate and at what speed. So, I made it possible to increment and send numbers at regular intervals from my own serial monitor and Android app(Android-nRF-UART).

I experimented in the following way.

1. The sample "ble_app_uart" of SDKv16.00 was written in nRF52832. 
2.  I installed "Android-nRF-UART (slightly edited)" on my Android tablet (Android 7.0) using Android studio.
3. Windows PC via uart and monitor it with a serial monitor of my own making.

First, we tested the communication from the serial monitor to the Android app.(serial monitor -> Android app)

The results were as follows.

loop count	interval(ms)	result	Notes
10	0	failure	"ble_app_uart" stopped
10	5	success
100	5	failure	"ble_app_uart" stopped
100	10	success
1000	10	failure	"ble_app_uart" stopped

Next, we tested the communication from the Android app to the serial monitor.(Android app -> serial monitor)

The results were as follows.

loop count	interval(ms)	result	Notes
10	0	success	There's more time lag than a serial monitor.(?)
100	0	failure	40 failures occurred.
100	5	success
1000	5	failure	The data does not reach around 250 times.
1000	10	failure	Around 350 times, the data is skipped until about 600 times. And it doesn't reach the end. However, it does not stop "ble_app_uart". The sender has completed the loop to the end.
1000	40	success
10000	40	failure	Around 1350 times, the data is skipped until about 1500 times.  And it doesn't reach the end. However, it does not stop "ble_app_uart". The sender has completed the loop to the end.

Question

1. What are some possible causes of why apps(ble_app_uart) stop?
2. What could be the cause of the skipped numbers on the receiving end?
3. How much throughput is allowed in nRF52832?

Thank you.

[Vidar Berg]

Hi,

1. You may get the "overrun error" (see ERRORSRC) if the UART transfer speed exceeds the transfer speed of your BLE link. The reason for this is that the send loop will become blocking while waiting for the NRF_ERROR_RESOURCES error to clear and thus prevent the UARTE buffer from being read.

To confirm that this is indeed the problem, try to comment out the code shown below from your UART event handler and see if it still stops:

        /* Handle UARTE communications errors. Comment APP_ERROR_HANDLER() to ignore lost packets */
        case APP_UART_COMMUNICATION_ERROR:
            APP_ERROR_HANDLER(p_event->data.error_communication);
            break;

This will make the FW ignore any communication errors on the UART interface.

2. Have you done any customizations to the original ble_app_uart example? Packets will get sent as long as ble_nus_data_send() returns NRF_SUCCESS (ie link will be terminated if not)

3. Throughput is likely going to be limited by the tablet in this case. Particularly if you are testing with an older Model running Android 7. Throughput numbers with nRF52's on both sides of the link can be found in the Softdevice specification here: Bluetooth Low Energy data throughput

Note that the UART v.2.0 mobile app has replaced by the UART app in nRF Toolbox. 

[mamorudeta]

Hi, Vidar Berg

Thank you for your quick reply.

1. Commenting out as you answered did not result in an error. In addition, when I checked "p_event->data.error_communication", I found it to be "1", indicating that it was a buffer overrun.

2. This was due to the fact that the Android application did not check for sending errors.

I have one more new question.

I changed the Android application to "Android nRF Toolbox" and made a few changes to it as a testing tool in the same way.
When sending data from the serial monitor to the Android application side at high speed, the missing data occurred. As a trial, I made the function immediately after receiving the data to output the received data to the log.

// UARTService.java for Android-nRF-ToolBox
public class UARTService extends BleProfileService implements UARTManagerCallbacks {
    ...
    @Override
    public void onDataReceived(@NonNull final BluetoothDevice device, final String data) {
        Log.d(TAG, data);
        ...
    }
    ...
}

However, at this point I found it to be missing. This problem did not occur when using "Android-nRF-UART".
What do you think is the cause?

[Vidar Berg]

Hi,

1. Would it make sense to put more data in each packet rather than having several small packets? That will lower the overhead and increase the throughput significantly. Each notification packet can be 'm_ble_nus_max_data_len' bytes long.

2. It would allow you to queue more packets without getting the NRF_ERROR_RESOURCES  error, but it won't prevent the error if you send data fast enough. 

3. This is a generic and common error from Android that can mean a lot of things. It's often related to sudden disconnects. I'd suggest to debug the FW side to see if any error or disconnect events occur.

[mamorudeta]

Hi, Vidar Berg

Thank you for your reply.

"m_ble_nus_max_data_len" was already set to a maximum value of 247.

1. Is there any way to shorten the connection interval for Android apps?

2. Do you know how to turn off "D/BluetoothGatt: onNotify()~" in Android app's log when receiving data?

3. Is there any other way to improve the speed on the android app side?

[Vidar Berg]

Hi,

mamorudeta said:

"m_ble_nus_max_data_len" was already set to a maximum value of 247.

That means you could have sent the data in one 70 byte package instead of 10 7-byte packets.

1. Shorter connection intervals should be requested by the peripheral which you can do by adjusting the MIN_CONN_INTERVAL and MAX_CONN_INTERVAL settings in main.c.

For selecting connection parameters I'd suggest you follow the recommendations given in the Apple accessory design guidelines, section 35.6 (link). Phones will generally accept the connection param update requests if you follow these.

2. I'm not sure, unfortunately.

3. The throughput is limited because you are splitting the data into multiple smaller notifications packets.

[mamorudeta]

Hi, Vidar Berg

Thank you for your quick reply.

I'm sorry for the confusion. We've already tried to send it in 247 bytes. As a result, it's only slightly faster.

[Vidar Berg]

Hi, I see. Could you try the modified example attached below and see if it gives you better results? I got around 66 kbps with my iPhone 8. The transfer speed is printed out on RTT. 

ble_app_uart.zip

[mamorudeta]

Hi, Vidar Berg

Thank you for your quick reply.

I tried it with the file you attached (I only had Android).
The result was about 26~30 kbps. Android-nRF-UART, Android-nRF-ToolBox, and my own application all had similar results.

[Vidar Berg]

Hi,

Sorry, I looked over the project again and see that I had configured NRF_SDH_BLE_GAP_DATA_LENGTH to 27 instead of 251. I had also kept the default NRF_SDH_BLE_GAP_EVENT_LENGTH setting. Both of these will have a significant impact on the transfer speed given that the phone you are connected to support the same configuration.

Please try the attached configuration and see if you can get closer to the numbers listed in the Softdevice specification.

New configuration tested with Google Pixel 2 running Android 10:

Attachment:

pca10040_throughput_fix.zip

[mamorudeta]

Hi, Vidar Berg

Thank you for your quick reply.

I tried it with the attached settings. In my environment, it was about 80~100 kbps. Overall, it's now up to 72 kbps, which is much faster than before.
Let me just ask one last question.
The following log is output when bonding with Android 7.0.

<debug> nrf_ble_gatt: ATT MTU updated to 247 bytes on connection 0x0 (response).
<info> app: Data len is set to 0xF4(244)
<debug> app: ATT MTU exchange completed. central 0xF7 peripheral 0xF7
<debug> nrf_ble_gatt: Data length updated to 27 on connection 0x0.
<debug> nrf_ble_gatt: max_rx_octets: 27
<debug> nrf_ble_gatt: max_tx_octets: 27

max_tx_octets(and max_rx_octets?) is going to be 247, why is it 27?

 And where can I change this setting?

[Vidar Berg]

Hi,

This means that the BT chipset on your phone does not support longer data packets (ie the 244 byte payload will be split into multiple 27-byte radio packets on-air).

[mamorudeta]

Hi, Vidar Berg

Thank you for your quick reply.

I understand.
It was really helpful. Thank you for your long term relationship with us.