HID endpoint clarification (feature reports)

[SmallerPond]

I'm trying to wrap my head around the APP_USBD driver, but I'm running into a mental block.  I am implementing a report descriptor for the Battery System usage page, and all of the characteristics are features.  So would I use an in or out endpoint? or both?  I'm in the middle of trying this now and I'm not getting an error, but I'm not seeing the endpoint on the host either - so I'm not sure if this is caused by the endpoint definition or the report.

It has also lead me down a bit of a rabbit hole.  I actually have a composite device with two endpoints working nicely (joystick and keyboard).  When I was adding on this third piece, I remembered that the default keyboard descriptor from the example has an output in it, but there is only an in endpoint.  So this has me feeling like I don't understand what's going on.  Shouldn't there also have to be an out endpoint for the keyboard to get the output from the host?  I thought I would try it, but when I added an out endpoint, the GLOBAL_DEF macro didn't like it and I'm not sure why:

#define HID_KEYBOARD_EPIN       NRF_DRV_USBD_EPIN(2)
#define HID_KEYBOARD_EPOUT       NRF_DRV_USBD_EPOUT(1)

#define ENDPOINT_LIST_KEYBOARD() \
(                           \
        HID_KEYBOARD_EPIN,  \
        HID_KEYBOARD_EPOUT  \
)

APP_USBD_HID_KBD_GLOBAL_DEF(m_app_hid_keyboard,
                            HID_KEYBOARD_INTERFACE,
                            ENDPOINT_LIST_KEYBOARD(),
                            hid_kbd_user_ev_handler,
                            APP_USBD_HID_SUBCLASS_NONE);

gives an "initializer element is not constant" error:

7> Compiling ‘main.c’
7> In file included from ../../../../../../components/libraries/usbd/class/hid/kbd/app_usbd_hid_kbd.h:58,
7>                  from C:\some_path\main.c:96:
7> ../../../../../../components/libraries/usbd/class/hid/kbd/app_usbd_hid_kbd_internal.h:116:1: error: initializer element is not constant
7> ../../../../../../components/libraries/util/app_util.h:712:37: note: in expansion of macro 'APP_USBD_HID_KBD_INTERVAL'
7> ../../../../../../components/libraries/util/nordic_common.h:118:31: note: in expansion of macro 'MACRO_MAP_1'
7> ../../../../../../components/libraries/util/app_util.h:700:29: note: in expansion of macro 'MACRO_MAP_N_'
7> ../../../../../../components/libraries/util/app_util.h:679:25: note: in expansion of macro 'MACRO_MAP_N'
7> ../../../../../../components/libraries/util/app_util.h:678:24: note: in expansion of macro 'MACRO_MAP_'
7> ../../../../../../components/libraries/usbd/class/hid/kbd/app_usbd_hid_kbd_internal.h:167:52: note: in expansion of macro 'MACRO_MAP'
7> ../../../../../../components/libraries/usbd/class/hid/kbd/app_usbd_hid_kbd.h:233:9: note: in expansion of macro 'APP_USBD_HID_KBD_GLOBAL_DEF_INTERNAL'
7> C:\some_path\main.c:619:1: note: in expansion of macro 'APP_USBD_HID_KBD_GLOBAL_DEF'
7> ../../../../../../components/libraries/usbd/class/hid/kbd/app_usbd_hid_kbd_internal.h:116:1: note: (near initialization for 'm_app_hid_keyboard_ep')
7> ../../../../../../components/libraries/util/app_util.h:712:37: note: in expansion of macro 'APP_USBD_HID_KBD_INTERVAL'
7> ../../../../../../components/libraries/util/nordic_common.h:118:31: note: in expansion of macro 'MACRO_MAP_1'
7> ../../../../../../components/libraries/util/app_util.h:700:29: note: in expansion of macro 'MACRO_MAP_N_'
7> ../../../../../../components/libraries/util/app_util.h:679:25: note: in expansion of macro 'MACRO_MAP_N'
7> ../../../../../../components/libraries/util/app_util.h:678:24: note: in expansion of macro 'MACRO_MAP_'
7> ../../../../../../components/libraries/usbd/class/hid/kbd/app_usbd_hid_kbd_internal.h:167:52: note: in expansion of macro 'MACRO_MAP'
7> ../../../../../../components/libraries/usbd/class/hid/kbd/app_usbd_hid_kbd.h:233:9: note: in expansion of macro 'APP_USBD_HID_KBD_GLOBAL_DEF_INTERNAL'
7> C:\some_path\main.c:619:1: note: in expansion of macro 'APP_USBD_HID_KBD_GLOBAL_DEF'
7> In file included from ../../../../../../components/libraries/usbd/app_usbd.h:46,
7>                  from C:\some_path\main.c:92:
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:463:18: error: initializer element is not constant
7> ../../../../../../components/libraries/util/app_util.h:747:41: note: in expansion of macro 'APP_USBD_CLASS_IFACE_EP_EXTRACT_1__'
7> ../../../../../../components/libraries/util/nordic_common.h:118:31: note: in expansion of macro 'MACRO_MAP_REC_1'
7> ../../../../../../components/libraries/util/app_util.h:708:33: note: in expansion of macro 'MACRO_MAP_REC_N_'
7> ../../../../../../components/libraries/util/app_util.h:687:29: note: in expansion of macro 'MACRO_MAP_REC_N'
7> ../../../../../../components/libraries/util/app_util.h:686:28: note: in expansion of macro 'MACRO_MAP_REC_'
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:460:17: note: in expansion of macro 'MACRO_MAP_REC'
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:457:17: note: in expansion of macro 'APP_USBD_CLASS_IFACE_EP_EXTRACT_1_'
7> ../../../../../../components/libraries/util/nordic_common.h:118:31: note: in expansion of macro 'APP_USBD_CLASS_IFACE_EP_EXTRACT_1'
7> ../../../../../../components/libraries/util/nordic_common.h:116:31: note: in expansion of macro 'CONCAT_2_'
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:440:9: note: in expansion of macro 'CONCAT_2'
7> ../../../../../../components/libraries/util/app_util.h:712:37: note: in expansion of macro 'APP_USBD_CLASS_IFACE_EP_EXTRACT_'
7> ../../../../../../components/libraries/util/nordic_common.h:118:31: note: in expansion of macro 'MACRO_MAP_1'
7> ../../../../../../components/libraries/util/app_util.h:700:29: note: in expansion of macro 'MACRO_MAP_N_'
7> ../../../../../../components/libraries/util/app_util.h:679:25: note: in expansion of macro 'MACRO_MAP_N'
7> ../../../../../../components/libraries/util/app_util.h:678:24: note: in expansion of macro 'MACRO_MAP_'
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:583:5: note: in expansion of macro 'MACRO_MAP'
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:811:29: note: in expansion of macro 'APP_USBD_CLASS_IFACES_EP_EXTRACT'
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:946:9: note: in expansion of macro 'APP_USBD_CLASS_INSTANCE_INITVAL'
7> ../../../../../../components/libraries/usbd/class/hid/kbd/app_usbd_hid_kbd_internal.h:169:5: note: in expansion of macro 'APP_USBD_CLASS_INST_GLOBAL_DEF'
7> ../../../../../../components/libraries/usbd/class/hid/kbd/app_usbd_hid_kbd.h:233:9: note: in expansion of macro 'APP_USBD_HID_KBD_GLOBAL_DEF_INTERNAL'
7> C:\some_path\main.c:619:1: note: in expansion of macro 'APP_USBD_HID_KBD_GLOBAL_DEF'
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:463:18: note: (near initialization for 'm_app_hid_keyboard.specific.iface.ep[0].address')
7> ../../../../../../components/libraries/util/app_util.h:747:41: note: in expansion of macro 'APP_USBD_CLASS_IFACE_EP_EXTRACT_1__'
7> ../../../../../../components/libraries/util/nordic_common.h:118:31: note: in expansion of macro 'MACRO_MAP_REC_1'
7> ../../../../../../components/libraries/util/app_util.h:708:33: note: in expansion of macro 'MACRO_MAP_REC_N_'
7> ../../../../../../components/libraries/util/app_util.h:687:29: note: in expansion of macro 'MACRO_MAP_REC_N'
7> ../../../../../../components/libraries/util/app_util.h:686:28: note: in expansion of macro 'MACRO_MAP_REC_'
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:460:17: note: in expansion of macro 'MACRO_MAP_REC'
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:457:17: note: in expansion of macro 'APP_USBD_CLASS_IFACE_EP_EXTRACT_1_'
7> ../../../../../../components/libraries/util/nordic_common.h:118:31: note: in expansion of macro 'APP_USBD_CLASS_IFACE_EP_EXTRACT_1'
7> ../../../../../../components/libraries/util/nordic_common.h:116:31: note: in expansion of macro 'CONCAT_2_'
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:440:9: note: in expansion of macro 'CONCAT_2'
7> ../../../../../../components/libraries/util/app_util.h:712:37: note: in expansion of macro 'APP_USBD_CLASS_IFACE_EP_EXTRACT_'
7> ../../../../../../components/libraries/util/nordic_common.h:118:31: note: in expansion of macro 'MACRO_MAP_1'
7> ../../../../../../components/libraries/util/app_util.h:700:29: note: in expansion of macro 'MACRO_MAP_N_'
7> ../../../../../../components/libraries/util/app_util.h:679:25: note: in expansion of macro 'MACRO_MAP_N'
7> ../../../../../../components/libraries/util/app_util.h:678:24: note: in expansion of macro 'MACRO_MAP_'
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:583:5: note: in expansion of macro 'MACRO_MAP'
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:811:29: note: in expansion of macro 'APP_USBD_CLASS_IFACES_EP_EXTRACT'
7> ../../../../../../components/libraries/usbd/app_usbd_class_base.h:946:9: note: in expansion of macro 'APP_USBD_CLASS_INSTANCE_INITVAL'
7> ../../../../../../components/libraries/usbd/class/hid/kbd/app_usbd_hid_kbd_internal.h:169:5: note: in expansion of macro 'APP_USBD_CLASS_INST_GLOBAL_DEF'
7> ../../../../../../components/libraries/usbd/class/hid/kbd/app_usbd_hid_kbd.h:233:9: note: in expansion of macro 'APP_USBD_HID_KBD_GLOBAL_DEF_INTERNAL'
7> C:\some_path\main.c:619:1: note: in expansion of macro 'APP_USBD_HID_KBD_GLOBAL_DEF'
Build failed

which I don't understand.  How could it not be constant?  I got the endpoints the same way I did when there was only one of them.

Anyway, I think maybe I have asked too many questions here, but I'm not 100% if I'm asking the right things so I'm hoping that there is an answer that kind of gets everything since they are related.  If this is wrong, I can always break this into different questions.  Then I can also make another one for my confusion about what the interface parameter does... :-P

[ovrebekk]

Hi

What does your report descriptor look like?

Is it based on the one in the USB HID Usage Table document?

Feature and out reports can use either an output interrupt endpoint or the control endpoint. The control endpoint is always present, so technically no OUT endpoint is needed, which is why the keyboard descriptor can support output reports without configuring an OUT endpoint. 

Best regards
Torbjørn

[SmallerPond]

The report is based on the usage table doc for HID power devices (cf. the chapter on Battery System and the example in Appendix A here, especially section A.6.9).  Generally, I am doing okay with creating descriptors I think.  I'm just a little fuzzy on getting and setting them using the app_usbd driver, and what the interplay is between endpoints, interfaces, and descriptors in the actual implementation.  Here is the descriptor, I can either use it at its own endpoint, or include it as a on the joystick or keyboard descriptor (I think, no?):

#define HID_BATT_REPORT_DESC() {  \
    0x05, 0x85,                    /* USAGE_PAGE (Battery System) */ \
 \
    0x09, 0x18,                    /* USAGE (BatteryInsertion) */ \
    0x75, 0x01,                    /* REPORT_SIZE (1) */ \
    0x95, 0x01,                    /* REPORT_COUNT (1) */ \
    0x15, 0x00,                    /* LOGICAL_MINIMUM (0) */ \
    0x25, 0x01,                    /* LOGICAL_MAXIMUM (1) */ \
    0xb1, 0x03,                    /* FEATURE (Cnst,Var,Abs) */ \
 \
    0x09, 0x2c,                    /* USAGE (CapacityMode) */ \
    0x75, 0x01,                    /* REPORT_SIZE (1) */ \
    0x95, 0x01,                    /* REPORT_COUNT (1) */ \
    0xb1, 0x03,                    /* FEATURE (Cnst,Var,Abs) */ \
 \
    0x75, 0x06,                    /* REPORT_SIZE (6) */ \
    0x95, 0x01,                    /* REPORT_COUNT (1) */ \
    0xb1, 0x03,                    /* FEATURE (Cnst,Var,Abs)  ; end byte 1 */ \
 \
    0x09, 0x83,                    /* USAGE (DesignCapacity) */ \
    0x75, 0x18,                    /* REPORT_SIZE (24) */ \
    0x95, 0x01,                    /* REPORT_COUNT (1) */ \
    0x67, 0x01, 0x10, 0x10, 0x00,  /* UNIT (SI Lin:Battery Capacity) */ \
    0x55, 0x00,                    /* UNIT_EXPONENT (0) */ \
    0x15, 0x00,                    /* LOGICAL_MINIMUM (0) */ \
    0x27, 0xfe, 0xff, 0xff, 0x00,  /* LOGICAL_MAXIMUM (16777214) */ \
    0xb1, 0x03,                    /* FEATURE (Cnst,Var,Abs)  ; end byte 1 + 3 = 4 */ \
 \
    0x09, 0x66,                    /* USAGE (RemainingCapacity) */ \
    0x75, 0x24,                    /* REPORT_SIZE (36) */ \
    0x95, 0x01,                    /* REPORT_COUNT (1) */ \
    0x67, 0x01, 0x10, 0x10, 0x00,  /* UNIT (SI Lin:Battery Capacity) */ \
    0x55, 0x00,                    /* UNIT_EXPONENT (0) */ \
    0xb1, 0x03,                    /* FEATURE (Cnst,Var,Abs)  ; end byte 4 + 4 = 8, start byte 9 with 4 bits */ \
 \
    0x75, 0x04,                    /* REPORT_SIZE (4) */ \
    0x95, 0x01,                    /* REPORT_COUNT (1) */ \
    0xb1, 0x03,                    /* FEATURE (Cnst,Var,Abs)  ; end byte 9 */ \
 \
    0x09, 0x42,                    /* USAGE (BelowRemainingCapacityLimit) */ \
    0x09, 0x44,                    /* USAGE (Charging) */ \
    0x09, 0x45,                    /* USAGE (Discharging) */ \
    0x75, 0x01,                    /* REPORT_SIZE (1) */ \
    0x95, 0x03,                    /* REPORT_COUNT (3) */ \
    0x15, 0x00,                    /* LOGICAL_MINIMUM (0) */ \
    0x25, 0x01,                    /* LOGICAL_MAXIMUM (1) */ \
    0x65, 0x00,                    /* UNIT (None) */ \
    0xb1, 0x03,                    /* FEATURE (Cnst,Var,Abs)  ; start byte 10 with 3 bits */ \
 \
    0x75, 0x05,                    /* REPORT_SIZE (5) */ \
    0x95, 0x01,                    /* REPORT_COUNT (1) */ \
    0xb1, 0x03                     /* FEATURE (Cnst,Var,Abs)  ; +5bits = end byte 10 */ \
}

As I said before, I try to give it it's own endpoint, but I get an error using the macro APP_USBD_HID_KBD_GLOBAL_DEF.  The most important information first is to know what is the preferred way to set up a report descriptor like this one?

Then, once I get it setup without throwing errors, I have no idea how to set the feature reports (I found this for BLE HID, but nothing for USBD) so some information about that would be appreciated.  Finally, if you are feeling particularly generous, maybe you could also clear up for me why I might use a separate endpoint for a new report descriptor vs just trying to append it to an existing descriptor?  Is it just if I plan on updating the data separately?

Thanks for your help!

[ovrebekk]

Hi Alberto

Sorry for the slow response. I just got back from several weeks of leave and will need some more time to try and test this on my end. 

Have there been any developments on your end in the mean time?

Best regards
Torbjørn

[Alberto Favero]

The system have been test on my side and there are no bugs now (I hope also when the customer will test it!).

There are just to need to reset the white list each time that a win10 O.S. need to connect with-out a disconnection in another before. But this one is another topic.

Pleas, have a quick look if there is anything working wrong in the BLE standard.

Best regards,

Alberto

[ovrebekk]

Hi Alberto

The example seems to work fine for me, at least the normal keyboard commands are received like normal. 

Best regards
Torbjørn

[Alberto Favero]

Thanks a lot,

have been tricky make it work correctly in the different OS (linux, win10, mac os).

Thanks for the test and the support.

Another question about the example. I need to delete the white list sometimes in the system. In particular with the win10 os. Is it possible avoid this? Meaby is another tread.

Best regards,

Alberto

[ovrebekk]

Hi Alberto

I can imagine there could be some complications getting everything running everywhere, yes. Please note I didn't try to send any data to your custom HID endpoint in Windows. Have you tried this already? 

I agree the whitelist issue is probably best for another case. Just include all the things you have tried, and any information relevant to the issue. 

Best regards
Torbjørn

[Alberto Favero]

Hi Torbjørn,

after 10 month the costumer add the BLE under windows 10 in the system and they checked it out.

The end-point out is not working.

I mean, is working only with the capslock / block num correctly under windows 10, but the general end-point is not working. In Linux Ubnuntu 20.04 is still working proprely!

Do you have any suggestion to make it work?

Need i to change the HID descriptor or add another composite pheriperal?

Gest regards,

Alberto

[Alberto Favero]

https://docs.microsoft.com/en-us/windows-hardware/drivers/hid/hid-architecture

Look-like I need to add a new end-point in the BLE HID device, make it composite like i did in the USB.

This allow windows to use:

0x0001

0x0006 - 0x0007

Yes

Yes

Yes

Keyboard / Keypad class driver and mapper driver

Exclusive

and the new hid pheriperal to send any end-point-out to the device.

Are you agree?

Do you have any example to add a new HID generic class to the BLE hid keyboard example?

Is really userfull the hid pheriperal to communicate with the O.S., is driverless ad usually it is working fine with any O.S.

Best regards,

Alberto

[ovrebekk]

Hi Alberto

Alberto Favero said:

Are you agree?

Do you have any example to add a new HID generic class to the BLE hid keyboard example?

I don't think we have such an example, but I will do some digging internally and see if I can find something relevant. 

Alberto Favero said:

Is really userfull the hid pheriperal to communicate with the O.S., is driverless ad usually it is working fine with any O.S.

Normally you would use USB CDC devices for this. They are also driverless (at least with Windows 10 and up), and provide a very simple comport interface that you can easily integrate with many different types of application or API's. 

Is there any reason you couldn't use CDC instead?

It is possible to set up both a standard HID endpoint and a CDC endpoint on the same device. 

Best regards
Torbjørn

[Alberto Favero]

Thanks for the quick response.

The customer asked for HID peripheral.

Looking forward if you find any BLE HID keyboard + END point out example.

Best regards,
Alberto

[ovrebekk]

Hi Alberto

I couldn't find any example showing how to do a custom HID endpoint over BLE unfortunately. The example I shared earlier is showing custom HID endpoint, but over USB. 

It should be possible to adapt some of this code (like the report descriptor) to utilize HID over GATT instead of HID over USB. 

Best regards
Torbjørn