Ps/2 adapter question

[P o n e.c.c.c.c.c if I can]

I've been looking at a ps/2 adapter and have been wondering if a usb to ps/2 adapter will make my keyboard latency to 1ms? Just like how ps/2 keyboard are. Oh and I disabled legacy usb on my motherboard so I'm gonna have to buy a ps/2 keyboard anyway . Answers will be helpful(*-*/)

[Uptivuptiz]

I think it depends on what the pulling rate is on the adapter. To get the 1ms response time would require a pulling rate of 1000Hz

[mariushm]

In theory, you can do polling up to 8000 Hz. In real world, most devices will be designed to support up to 1000 Hz.

 

You could use a microcontroller to simulate a simple usb 1.1 or usb 2.0 host and poll the usb keyboard at 1000hz, but I have doubts the controller inside will update more often than once every 5-10ms or so.

 

You want to be particularly careful with mechanical keyboards, because you have to handle debouncing - in simple terms when you press a mechanical key, it's not always an off-on-off ... for a ms or so, sometimes even more, there can be sporadic contact due to the design of the key (ex you lift finger off the key so contact breaks but then the spring inside the key starts extending and the contact is made again)

Most mechanical keys suggest a debounce time of up to 5ms ... for old keyboards this time can extend up to 10ms or so.

So the keyboard controller will scan the key matrix multiple times and then FILTER the readings to reduce/prevent debouncing, so even though the keys can be all scanned in less than 0.1ms, some keyboard controllers will probably scan for 1-2ms and filter results and then wait for the next usb polling (every 8ms for the default 125 Hz polling rate)

 

Anyway, the ps/2 is not particularly faster... by default it works at 100 Hz compared to usb's 125 Hz ... and it can only be raised up to around 200Hz.... the ps/2 goes to a Fast IO chip which then connects to chipset or whatever.... so 1ms updates are unlikely really to happen on ps/2

You usually want  ps/2 because it's more flexible when it comes to n-key rollover and stuff like that, not for latency reasons

 

See https://en.wikipedia.org/wiki/PS/2_port#Lower_Default_Latency_of_USB_Mice