Add a variable to allow easy modification of the keypress limit.

[ZDBioHazard]

If you need to be able to press more than 6 keys on your virtual keyboard, and you don't mind losing BIOS compatibility, the changes in this branch enable you to simply change #define KEYS_ROLLOVER to however many keys you need, and it will alter the USB descriptor, resize the data structures and handle the extra keys automatically!

Even with the default 6-key configuration, this implementation is 34 bytes smaller. 😉 (on my Leonardo, at least)

I haven't thought of a sensible way to tweak KEYS_ROLLOVER from the user side, but at least people won't have to dig into the meat of this library to modify the rollover limit for their keyboard-emulating game controllers and whatnot.

[facchinm]

LGTM! The code cleanup is enough to justify the merge, and the "configurable" keypress number could be useful for someone.
@NicoHood does your HID project handles more than 6 keypress?

[NicoHood]

Yes it does. The problem with this implementation is, that for u2 devices the HID reports are limited to 15 bytes + reportid. This means you should not set this variable higher than 15.

Other than 6 keys makes it bios incompatible, correct. But the arduino implementation is not bios compatible anyways.

My HID Project covers both needs: bios compatible and nkro keyboard with >100 keypresses at the same time. The question is, if the os can handle those.
https://github.com/NicoHood/HID/wiki/Keyboard-API#boot-keyboard
https://github.com/NicoHood/HID/wiki/Keyboard-API#nkro-keyboard

I am not against new usb functions, I really like to see people working on those things. But as the #define is just for proprietary use, it makes no sense to include it. And I think we (@facchinm and @cmaglie ) aggreed that the arduino libraries should keeps basic and simple and the HID Project should extend them.

If the implementation is not more reliable or smaller (you should test this!), I see no reason to add this. But if it does, feel free to open a PR at my project.

And also: This PR suffers from this missing feature too. I implemented it in the old times without arduino builder, but noone ever did for arduino-builder. It would make the code a lot simpler and compacter. This would give a breakable change to the IDE, but noone seems to care for now :( You might consider to finally have a look at this:
arduino/arduino-builder#15

[ZDBioHazard]

Awesome, I hadn't run across the @NicoHood HID library. It took a little work to get it to play nice with arduino-makefile, but it works like a champ. SingleNROKeyboard somehow even seems to be 246 bytes smaller than the unmodified Arduino implementation with my simple ::press() and ::release() test app. 👍

If you like, I could go back and rework this patch into a general cleanup and resubmit it. Maybe change the #define to _REPORT_KEYS and remove the "you can edit this" comments, but keep it around so there aren't hard-coded sixes everywhere. Plus people could still edit it if they really want to. 😉 Maybe I can fix #5 while I'm at it.

[NicoHood]

I think i will not break the special bios compatiblity if the nkro is even smaller and better than this. If it works good, just use it like that ;)

If #5 also applies to my project, let me know.

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