USB Keyboard : how to find scancode for specific functions ?

[spilz]

Hello everyone

i'm working on a project with a PIC18F2550 to use it as an USB keyboard.

I'm able to send ASCII properly, I'm able to send scancode from this list properly :

[Ttelmah]

This is one of those lovely complicated things.
Now start with the table you have found. This gives PS/2 scancodes. These
were the codes a keyboard device actually sent when connected to the old
PS/2 connector. Now these were interpreted internally inside the PC, so
pressing the ESC key gave a 1, and releasing it gave an 0x81. The internal
code in the PC, then translated this into the ESC being pressed and released
operations.
When USB launched, they decided to implement loads more possibilities than
the basic codes, so the handling moved away from these codes. Instead
you have a huge list of codes for the keys, and the operations on these
(some of which are latched, and some happen only when the corresponding
key is pressed), and the scancodes remain the same for the key involved.
So (for example), '?', returns the same key number as '/', but with
the shift set.
Now to make things worse, different keyboard manufacturers change where
things actually are on the keyboard.

Key list to pull is:
[url]
https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/translate.pdf&ved=2ahUKEwiv9o6UzsuHAxWWX0EAHQa5NQIQFnoECCYQAQ&usg=AOvVaw0qYepWO28gAp8NbbWWs5EY
[/url]

This lists every key Microsoft admit to, and their USB scancodes, together
with the PS/2press and release codes.

Now, some of the ones you are asking about are complex, since they are
not actually standard HID keyboard codes. They use usage pages other
than 7. This is because they are not actually functions originally assigned
to the 'keyboard'. 0xC is actually a 'consumer page' ID. So a character
coming from a special controller, not a keyboard. If you really need to
send these, you are actually going to have to implement another device
using this usage page, with it's own USB descriptor for this page. You
can potentially do this with a combined USB descriptor (look at the
example for kbmouse), so the driver effectively generates two USB
devices, one a keyboard, and the second (for your case), a consumer
controller.
Look at this thread about this:
[url]
https://stackoverflow.com/questions/55166120/combine-keyboard-consumer-control-in-descriptor
[/url]
In particular the last post here.
Do a search on 'USB composite device', for a lot about this.

[spilz]

Thanks a lot for you explanations

I’m going to try to do it the way you suggest

Have a good day

[vtrx]

Read these tips here.

https://www.ccsinfo.com/forum/viewtopic.php?t=59253&highlight=vtrx

[Ttelmah]

Good stuff.
Key point here is that he still needs to handle the composite device part,
since he wants both a keyboard and a multimedia controller, but this gives
most of the stuff for the latter.