Fail to interact with custom characteristics when its UUID is different from its service

[Dko]

Context

I followed these tutorials (which are great btw) and adapted them to have 2 custom services:

• Nordic UART Service (as provided in examples, no modification)
• My custom service

In my custom service I added 4 characteristics. All these characteristics share the same ble_uuid128_t base_uuid, which is different from the service they belong to.

• Service UUID: 0000FFFD-0000-1000-8000-00805F9B34FB
  
  • Char1:  CAFE0001-1234-1234-1234-123456789000
  • Char2:  CAFE0002-1234-1234-1234-123456789000
  • Char3:  CAFE0003-1234-1234-1234-123456789000
  • Char4:  CAFE0004-1234-1234-1234-123456789000

I use nRF Connect mobile app for Android to test my program.

Problem

When I try to interact (Read/Write/Enable notifications, ...) with my characteristic, the applications hangs forever.
In the logs, the last DEBUG frame is gatt.writeCharacteristic(CHAR_UUID, VALUE)

I tried to change the Service UUID so it matches the one from characteristics(CAFEFFFD-1234-1234-1234-123456789000)
And then that worked ! I was able to successfully Write/Read/etc.

I understand that I register my service UUID with sd_ble_gatts_service_add(), so the SoftDevice indexes the Service UUID.
However it seems that despite attaching my characteristic to the service handle with sd_ble_chracteristics_add(), it seems that some link is missing.
Like... the characteristic base UUID is not registered/indexed/?, only listed (because it appears OK in the Service/Char list after connection and discovery).
I am confused.

Notes:

• I have set vs_uuid_count to 3 (NUS UUID, Custom service UUID, Custom characteristic UUID). I also tried with 2 with no effect.
• The RAM is adapted correctly so I have no warning with soft_device_enable()
• I only advertise my custom service, (not the NUS) but when I connect I see all my services and characteristics with the correct UUIDs
• The NUS service is working as expected, no matter the configuration used for the custom service

[Nguyen Hoan Hoang]

The service and characteristics must belong to the same base uuid.  You can change the 16bits value for the service/char uuid.  Assuming your base uuid is CAFE0000-1234-1234-1234-123456789000,  your service/char uuid is the xxxx values CAFExxxx-1234-1234-1234-123456789000   

[Dko]

Thanks for the quick reply. However before posting my question I came across these topcis and it was my understanding that it was actually possible to have different base UUIDs for service and characteristics:

• https://devzone.nordicsemi.com/f/nordic-q-a/36380/fully-different-with-128-bit-uuid-for-service-and-characteristic
• https://devzone.nordicsemi.com/f/nordic-q-a/35733/definition-of-a-different-uuid-for-a-characteristic
• https://devzone.nordicsemi.com/f/nordic-q-a/16446/different-uuids-for-characteristics
• https://devzone.nordicsemi.com/f/nordic-q-a/10182/can-you-have-different-base-uuid-for-characteristics-in-a-service
• devzone.nordicsemi.com/.../128-bit-characteristic-uuid-not-based-on-service-uuid

Did I miss something ?

[Nguyen Hoan Hoang]

I've always though it has to be the same base.  Seems like it doesn't have to.  Then there is no problem in this case.