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Author Topic: KRO and USB 2.0 vs 3.0  (Read 2462 times)

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Offline roknir

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KRO and USB 2.0 vs 3.0
« on: Thu, 23 February 2012, 12:28:43 »
As I understand it, if a keyboard uses USB 2.0, no rollover better than 6KRO can be achieved, while PS/2 can have true NKRO.  With USB 3.0 becoming more popular, is the limitation going to be the same?  Will USB 3.0 be limited to 6KRO also or could it do NKRO?
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Offline stingrae

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KRO and USB 2.0 vs 3.0
« Reply #1 on: Thu, 23 February 2012, 13:46:22 »
Quote from: roknir;523245
As I understand it, if a keyboard uses USB 2.0, no rollover better than 6KRO can be achieved, while PS/2 can have true NKRO.  With USB 3.0 becoming more popular, is the limitation going to be the same?  Will USB 3.0 be limited to 6KRO also or could it do NKRO?


USB works on polling devices while ps/2 works on well accepting input when it occurs, the behaviour of usb hasnt changed only the bandwidth (afaik, I may be wrong though). Btw you get over 12 kro on some keyboards without emulating keyboards.
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Offline alaricljs

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KRO and USB 2.0 vs 3.0
« Reply #2 on: Thu, 23 February 2012, 13:59:58 »
Not to mention on teensy KB controllers there's working NKRO on USB.
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Offline daniel0731ex

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KRO and USB 2.0 vs 3.0
« Reply #3 on: Thu, 23 February 2012, 15:14:05 »
I thought the 3.0 was a complete makeover in the internal design.
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Offline stingrae

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KRO and USB 2.0 vs 3.0
« Reply #4 on: Thu, 23 February 2012, 15:55:45 »
Quote from: daniel0731ex;523425
I thought the 3.0 was a complete makeover in the internal design.


Yes but not necessarily the way it works in an OS...

The issue with rollover by usb has never been a transfer speed issue afaik. I dont think its possible to poll more actions than 6 unless trickery (ducky or noppoo) or clever electronics (leopold 21 kro).
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Offline Soarer

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KRO and USB 2.0 vs 3.0
« Reply #5 on: Thu, 23 February 2012, 18:44:58 »
Well there won't be any USB 3.0 keyboards, so that question is moot!

I'm not even sure that any are even using full-speed USB; almost all, if not all, are low-speed devices.

Low-speed is tricky to do more than 6KRO, mainly because a packet is limited to 8 bytes. A report can be larger than a packet, or tricks with multiple endpoints (e.g. pretending to be more than one keyboard) can be used, but history tells us these aren't easy to make 100% compatible.

Teensy-based mods use full-speed, so have more freedom. My converter uses a 23 byte report - big enough to have one bit for each useful keyboard HID code (all 172 of them!). And then it's not a big problem to make NKRO 100% compatible.
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