Writing Values to Characteristics in the Image Transfer Demo

[richardcoffey]

Hello, I've set up the image transfer app from Nordic Playground with the idea in mind to remove the Android App from the equation. I've picked through the Android app itself, and have found the characteristics advertised on the Nordic nrf52-DK necessary to capture images from an Arducam and transmit them over BLE as intended. 

public static final UUID IMAGE_TRANSFER_SERVICE_UUID = UUID.fromString("6e400001-b5a3-f393-e0a9-e50e24dcca3e");
public static final UUID RX_CHAR_UUID       = UUID.fromString("6e400002-b5a3-f393-e0a9-e50e24dcca3e");
public static final UUID TX_CHAR_UUID       = UUID.fromString("6e400003-b5a3-f393-e0a9-e50e24dcca3e");
public static final UUID IMG_INFO_CHAR_UUID = UUID.fromString("6e400004-b5a3-f393-e0a9-e50e24dcca3e");

Above are the three UUID's that I have been writing to via the nrfConnect app. Using nRFConnect, I turned on notifications for UUID's 6e400003 and 6e400004. Then, according to the Android app, writing "0x01" to UUID 6e400002 should trigger a "StartSingleCapture". This is confirmed to work on the nRFConnect app, and I can see the picture data being transferred over.

However, when using the ubuntu tool Bluetoothctl, it seems like writing to the UUID 6e400002 does not trigger a notification on neither of the UUID's 6e400003 and 6e400004. According to a bluetooth sniffer, I am sending the data over, I'm just not getting a response from the Nordic board. Clearly this could be due to a variety of issues, but I wanted to reach out and ask if anyone on the Nordic team has had experience writing values to the nrf52DK using the bluetoothctl tool (version 5.50).

The goal of this experiment is to be able to trigger an image transfer from the stock Nordic image transfer code on the nrf52, and receive the notification data on the linux side sending the data, essentially sidestepping the Android app all together. 

If you need any more information, please reach out.

[richardcoffey]

Hi Tor,

So I tested out the "ble_app_uart" demo on the nordic board, and I was successfully able to write to the device using my Bluetoothctl tool on the Linux device that has been having trouble. 

When I write data from Linux device, the data shows up on the Serial port that the nordic device is connected to. Additionally, I was also able to write to that same serial port and have the data propagate up through the notify channel back to my tool on the Linux device

So as far as I can tell, this UART demo works perfectly on my system. That seems to confirm that the odd behavior on the image transfer program is isolated to just that program, and the way my bluetooth chip handles the interaction.

[ovrebekk]

Hi Richard

Do you have some sort of BLE sniffer so you can see what's happening over the air when the Linux device is communicating with the image transfer demo?

Then I might be able to spot the issue without needing to test it myself on the same hardware. 

Best regards
Torbjørn

[richardcoffey]

Hi Tor,

I made a post in this thread on October 23rd, 2019 at 16:22 with bluetooth sniffer logs. There are pictures of connections, and attempted image transfers on both the working and the non working devices. 

[ovrebekk]

Hi

That's the HCI log on the Linux side I believe?

I am thinking of sniffer trace of what is happening over the air, similar to what you get from an Ellisys or Frontline Bluetooth sniffer, or the free Nordic sniffer. 

Best regards
Torbjørn