Multiple HID services - what are essential HID characteristics

[Matthew K]

Hi guys. May I ask some questions regarding ble_app_hids_keyboard_pca10056_s113 project from 17.1.0 nRF5 SDK:

From my previous question,

 RE: HID report map data size limit? 

I have a HID report descriptor exceeding 512 so I'm planning to create multiple HID services by modifying the ble_app_hids_keyboard_pca10056_s113  example, like HID A / HID B / HID C

In the ble_app_hids_keyboard_pca10056_s113  example, there are

2A4E Protocol mode

2A4B Report map

2A22 Boot keyboard

2A4D Report (Input, output, feature total 3 characteristics)

2A4A HID info

2A4C HID control point

For other HID services, I expect report map and report characteristics should be added. What about Protocol mode / HID info / HID control point?

Should every HID Service have Protocol mode / HID info / HID control point to work properly with iOS / Android / Windows / Linux devices?

Curious whether these are mandatory. Thanks for your help!

[Hung Bui]

Hi Matthew, 
Could you tell what exactly you want to achieve by having multiple HID services in your device ? 
Are you planning to make the device acts as multiple keyboard/mouse ? 
I am not so sure if the host would support that when you have multiple HID services. 

Regarding the characteristics, you can find this in the HID service specification 

O is optional and M is mandatory. For Cx , you would need to read the note. 

One customer has combined a mouse and keyboard in the same report here. It might be useful for you. 

[Matthew K]

Hi Hung.

Hung Bui said:

I am not so sure if the host would support that when you have multiple HID services. 

Really? My nRF52 device seems to work with Android at the moment when having

1 BAS + 1 DIS + 2 HIDS

May I ask what are the cases when a BLE client doesn't support multiple HID service?

Hung Bui said:

One customer has combined a mouse and keyboard in the same report here. It might be useful for you. 

Thanks, I also read  BLE HID Mouse and BLE HID keyboard integration in the same program with nrf52 dk. Need urgent help 

but my case is that the HID report descriptor exceeds 512 bytes.

I believe in this thread  RE: HID report map data size limit?  , Kenneth confirmed to split HIDS if the report map is bigger than 512 bytes.

Hung Bui said:

Are you planning to make the device acts as multiple keyboard/mouse ? 

Thank you for that screenshot. I plan to create Keyboard + Mouse + special feature reports. Due to my additional special feature reports in the report map, I need to split the HID service.

From this thread  How to test HID boot input and output using a PC , I recall boot characteristics are not supported by Windows.

So that means I can drop the Protocol mode characteristic, right?

[Hung Bui]

Hi Matthew, 
Thanks for letting me know. I'm no expert with HIDs, so I was not so sure if the host would detect multiple HID services then treat them as different devices. 

Matthew K said:

So that means I can drop the Protocol mode characteristic, right?

Yes if you don't plan to have the boot protocol mode. 

[Matthew K]

Sorry, but can I ask one more question?

For multiple HID services (HID A, HID B),

both A & B needs the two mandatory characteristics (HID Information and HID Control Point), right?

I was imagining whether HID A's mandatory characteristics can be used as a "global" characteristics for HID B.

[Hung Bui]

Hi Matthew, 

From my understanding they are mandatory for each service. I am not aware of "sharing" mandatory characteristics between services.