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AFAIK, it was mostly because a lot more PS/2 keyboards support N-key rollovers than USB keyboards.
by mavidser 8y ago
AFAIK, it was mostly because a lot more PS/2 keyboards support N-key rollovers than USB keyboards.
- NeedMoreTea 8y agoThat's because USB has an actual limitation so can't support n-key, just 5 or 6 I think. PS/2 does, but of course not all keyboards can deliver n-key even over PS/2.
- frostburg 8y agoUSB n-key rollover keyboards avoid that issue by looking like several keyboards to the OS, I think.
- Palomides 8y agothis is not true, USB HID has a 'boot protocol' mode for BIOS etc. which limits HID devices to 6KRO, but USB keyboards can send a report descriptor to an OS with as many keys at once as they want. see: https://deskthority.net/wiki/USB https://deskthority.net/wiki/USB
- NeedMoreTea 8y agoWell, the reality is that all USB mechanical and gaming keyboards have been limited to 6KRO until very recently. For instance: https://www.keyboardco.com/blog/index.php/2016/03/what-is-nkro-our-guide-to-rollover-anti-ghosting-and-choosing-the-right-keyboard/ https://www.keyboardco.com/blog/index.php/2016/03/what-is-nk... The very same keyboards provide n-key if you use the USB->PS/2 adaptor in the box with the keyboard. If it were straightforward there wouldn't be hacks such as pretending there's 2 keyboards in the system.
- clarry 8y agoImplementing it is straightforward, trivial even. As makomk hints, the problem is that you'd be doing something non-standard and thus have to rely on your own driver (or someone else's) rather than the system's built-in and ready-to-go hid drivers. Or you show up as multiple keyboards simultaneously, but that confuses some software.
- makomk 8y agoThe trouble is, if I recall correctly, that there's an awful lot of buggy driver code out there which cannot handle this correctly. So keyboards can't safely use this mode by default.