Exception on connection with nRF52 as connectivity chip

[gkovelman]

I'm using the pc-nrfutil v3.3.2 executable on Windows 10 which is using the ble driver v0.11.3. Connectivity chip is NRF52 on PCA10040.
I'm trying to perform secure buttonless DFU on my custom board.

The error that I'm seeing is:

x:\nrfutil\bin>nrfutil_332.exe -v dfu ble -pkg "pkg.zip" -ic NRF52 -p COM37 -n xxx -f
Shared library: C:\Users\Me\AppData\Local\Temp_MEI31~1\lib\win\x86_32\pc_ble_driver_shared_sd_api_v3.dll
Swig module name: pc_ble_driver_sd_api_v3
Board already flashed with connectivity firmware.
Using connectivity board at serial port: COM37
Sending Application image.

BLE: ble_enable with local ATT MTU: 247
BLE: Scanning for xxx
Received advertisement report, address: 0x705681D2C705, device_name:
Received advertisement report, address: 0x705681D2C705, device_name:
Received advertisement report, address: 0xD7D7784BF5B7, device_name:
Received advertisement report, address: 0xD7D7784BF5B7, device_name: xxx
BLE: Found target advertiser, address: 0xD7D7784BF5B7, name: xxx
BLE: Connecting to 0xD7D7784BF5B7
Received advertisement report, address: 0xDCA904951E08, device_name:
Received advertisement report, address: 0xD7D7784BF5B7, device_name:
BLE: Found target advertiser, address: 0xD7D7784BF5B7, name:
BLE: Connecting to 0xD7D7784BF5B7
Received advertisement report, address: 0xD7D7784BF5B7, device_name: xxx
BLE: Found target advertiser, address: 0xD7D7784BF5B7, name: xxx
BLE: Connecting to 0xD7D7784BF5B7
Received advertisement report, address: 0x4F351FA8E874, device_name:
Received advertisement report, address: 0x4F351FA8E874, device_name:
BLE: Connected to [215L, 215L, 120L, 75L, 245L, 183L]
ATT MTU exchanged: conn_handle=0 att_mtu=247
Successfully Connected
BLE: Service Discovery
Traceback (most recent call last):
File "nordicsemi_main_.py", line 871, in
File "site-packages\click\core.py", line 722, in call
File "site-packages\click\core.py", line 697, in main
File "site-packages\click\core.py", line 1066, in invoke
File "site-packages\click\core.py", line 1066, in invoke
File "site-packages\click\core.py", line 895, in invoke
File "site-packages\click\core.py", line 535, in invoke
File "nordicsemi_main_.py", line 747, in ble
File "nordicsemi\dfu\dfu.py", line 122, in dfu_send_images
File "nordicsemi\dfu\dfu.py", line 83, in _dfu_send_image
File "nordicsemi\dfu\dfu_transport_ble.py", line 453, in open
File "nordicsemi\dfu\dfu_transport_ble.py", line 147, in connect
File "site-packages\pc_ble_driver_py\ble_driver.py", line 124, in wrapper
File "site-packages\pc_ble_driver_py\ble_adapter.py", line 196, in service_discovery
TypeError: 'NoneType' object has no attribute 'getitem'
Failed to execute script main

Secure buttonless DFU is working with the iOS/Android apps/libraries, so my BLE profile is compatible.
This is also working correctly when the connectivity chip is nRF51 on PCA10031.
Log is the following:

x:\nrfutil\bin>nrfutil_332.exe -v dfu ble -pkg "pkg.zip" -ic NRF51 -p COM38 -n xxx -f
Shared library: C:\Users\Me\AppData\Local\Temp_MEI14~2\lib\win\x86_32\pc_ble_driver_shared_sd_api_v2.dll
Swig module name: pc_ble_driver_sd_api_v2
Flashing connectivity firmware...
Connectivity firmware flashed.
Using connectivity board at serial port: COM38
Sending Application image.
BLE: Scanning for xxx
Received advertisement report, address: 0xDCA904889157, device_name:
Received advertisement report, address: 0xD7D7784BF5B7, device_name:
Received advertisement report, address: 0xD7D7784BF5B7, device_name: xxx
BLE: Found target advertiser, address: 0xD7D7784BF5B7, name: xxx
BLE: Connecting to 0xD7D7784BF5B7
Received advertisement report, address: 0xDCA904889157, device_name:
Received advertisement report, address: 0xDCA904889157, device_name:
Received advertisement report, address: 0x479528C8E156, device_name:
BLE: Connected to [215L, 215L, 120L, 75L, 245L, 183L]
Successfully Connected
BLE: Service Discovery
Bonded Buttonless characteristic discovered -> Bond
etc...

[bihanssen]

Hi,
with ATT_MTU=247 it might be that the data is being sent to the bootloader too fast, we have seen this happen before. Could you try to reduce the MTU and see if that helps?

The pca10031 runs a softdevice that does not support MTU above 23, so that might explain why the problem is not occuring there.

[gkovelman]

So fast that the service discovery fails, even before the data transmission? Weird.

I'll try to reproduce this with ATT MTU=23

[bihanssen]

You're probably right, the error happens too fast for the MTU to be the issue here, unless in some indirect way.

[gkovelman]

Confirming that reducing the MTU helps with the issue. I modified to #define NRF_SDH_BLE_GATT_MAX_MTU_SIZE 23 and the PCA10040 could perform DFU.
Can we expect support for larger ATT MTU?

[bihanssen]

Related to NordicSemiconductor/pc-nrfutil#147
To be looked into.