BLE DFU example is not connectable

[mredp]

Hi,

I have been trying to get the BLE secure DFU example working on a custom board (nrf52840 - BC840 module). I tried it on SDK 15 and SDK 16. When I flash the BLE DFU, I can see it advertise on my mobile (nrfConnect) but I am unable to connect. 

I can, however, connect to it using nrfConnect on the PC. But I have noticed that the RSSI seems a little lower than usual anyhow.

You might think this is a hardware issue but:

• I flash, s140 6.1.1 softdevice + my app -> no issues
• I flash pre-compiled "secure dfu test images" -> no issues
• I compile the SDK 16 secure BLE DFU example, I make flash_softdevice + make flash -> issues
• I have also used the SDK 15 BLE DFU example but I needed to merge the softdevice and bootloader -> issues

My first idea to solve this was to check my sdk_config.h and make sure that the LF clock settings are correct. I have tried a number of settings without luck. I have on LF crystal on board, but even when I chose the RC clock, it had the same issue.

Finally, I have a nrf52832 dev board (BMD-350-EVAL). When I program the exact same example to the dev board it works fine. So my guess is there is something different about the nrf52832 vs nrf52840 examples/hardware. But I am not really sure.

You help is appreciated!

[mredp]

Ok I solved it,

I needed to change these lines in the sdk_config:

#define NRF_DFU_ANT_MTU 1024
#define NRF_DFU_BLE_MIN_CONN_INTERVAL 12

#define NRF_DFU_BLE_MAX_CONN_INTERVAL 12

Change them to:

#define NRF_DFU_ANT_MTU 247
#define NRF_DFU_BLE_MIN_CONN_INTERVAL 10

#define NRF_DFU_BLE_MAX_CONN_INTERVAL 15

Changing just the MTU or Just the connection interval didn't work. I had to change both. 

I am not 100% certain why this is necessary, I assume my phone can only handle certain values?

[mredp]

Sorry I spoke too soon, I am unable to replicate this success. I still am having issues connecting with my phone. Which is strange because I never have issues connecting with my own app - only when I flash the bootloader.

The error message is:

Connected to [MAC ADDRESS]
Connection parameters updae failed with status 8 (interval: 45.0ms, latency: 0, timeout: 5000ms)
Error 8 (0x8): GATT INSUF AUTHORIZATION
Error 8 (0x8): GATT CONN TIMEOUT
Disconnected

[mredp]

Another update. Once I OTA update the device using PC (nrfConnect). Then I can connect to my application using my phone.

So it appears that the only issue is that the my phone can't connect to the bootloader.