Linux 4.5 Input Updates Bring Changes Even For PS/2 Mice

[zanny]

Not sure why the article implies that there's something wrong with a PS/2 mouse. For the end user, there is absolutely no difference. Or wait, there is one, one more free USB slot...

PS/2 slots occupy space that usually fits two USB ports on motherboards.

The wrong part is that they are rare, barely used anymore, and thus consuming effort on everyones boot to search for devices maybe one person in a thousand has.

[caligula]

PS/2 slots occupy space that usually fits two USB ports on motherboards.

The wrong part is that they are rare, barely used anymore, and thus consuming effort on everyones boot to search for devices maybe one person in a thousand has.

Many modern mobos only have one PS/2 port. So it only uses one space. FWIW, it really depends on the chipset, how many USB ports you have. Some mobos have very small number of USB ports. I had one AMD system with 12 ports in the back and 2 in the front. Some systems only have 2-4 in the back. As already mentioned, some laptops use PS/2 internally.

[Shimon]

Besides, crap like keyboards repeating never happens(ed) on PS/2 - now go read about Rpi's or other SBC's problems with USB keyboards and mice. So yeah, the story is completely backwards.

[Iksf]

Another PS/2 keyboard user here. It's simpler, it's better (NKRO, less input delay), on Linux I can even hotplug PS/2 devices somehow which I'm pretty sure isn't meant to work but does anyway.... I get the argument for ditching them as a mobo designer or OS developer but as a user there's no reason to move away from them if you don't have to.

[Shimon]

It's possible to reinitialize the PS/2 devices via the /sys filesystem - not sure if you can actually boot without any and only then plug them in. You can definitely disconnect and reconnect at will as long as you don't swap the ports

[zanny]

Many modern mobos only have one PS/2 port. So it only uses one space. FWIW, it really depends on the chipset, how many USB ports you have. Some mobos have very small number of USB ports. I had one AMD system with 12 ports in the back and 2 in the front. Some systems only have 2-4 in the back. As already mentioned, some laptops use PS/2 internally.

I don't mean two individual PS/2 ports. One PS/2 port takes up the physical space of two USB ports, so if you were to have dual PS/2 ports for keyboard / mouse you are losing four usb ports total.

I've never seen a notebook advertising a trackpad as a ps/2 device personally, but I'd believe it could happen. It almost certainly shouldn't, though.

Another PS/2 keyboard user here. It's simpler, it's better

This is about PS/2 mouse polling though. PS/2 keyboards are common in the enthusiast space - I have one, for example. But PS/2 mice have been dead a long time since USB polling rates are more than sufficient to exceed the capabilities of PS/2 mice. There is no mechanical benefit to them at all, and thus using the universal interface is almost always the reasonable choice.

[maligor]

...and less latency (can be important for games).

How do you actually measure keyboard latency? I guess the only way is to disassemble the keyboard, attach a test jig to generate the signal straight off the board to avoid the mechanical latency and determine the control signal latency to a reasonable degree.

If you have any links to tests on it that aren't over 10 years old, I'd love to look at them too.

Additionally, PS/2 supports true n-key rollover (you can press as many keys as you want on your keyboard simultaneously and all will register correctly), while USB only supports up to 6 keys being pressed simultaneously. In some scenarios, this can be a deal-breaker.

My keyboard, for instance, has circuitry capable of n-key rollover, but it only works if I connect it to my PC over PS/2. The USB connection limits it to 6. I have seen keyboards that try to do fancy trickery to emulate it on USB (my friend has one), and it sorta works, but breaks other things ...

The 6 key limit on USB keyboards is bit of a myth, partially related to buggy BIOS code.

HID Keyboards are supposed to implement a boot keyboard mode which is infact limited to 6 keys, so that any firmware that handles the early boot doesn't have to deal with the entire HID specification and can essentially ignore the HID profile on the device.

When not in boot mode, they're only limited by the packet size of the USB operation mode and the HID profile can have anything you like. I've been meaning to test this out with some MCU's, since the HID spec does have a option of sending keys as a bitmap, and USB 2.0 should support large enough packets.

[Azrael5]

So developers don't know that PS/2 is an excellence and that not always what is modern is better.

one of the most rare ps/2 mouse made is 5 buttons very useful on gaming.

at least ps/2 keyboard is surely better than usb keyboard.

[nanonyme]

I don't mean two individual PS/2 ports. One PS/2 port takes up the physical space of two USB ports, so if you were to have dual PS/2 ports for keyboard / mouse you are losing four usb ports total.

I've never seen a notebook advertising a trackpad as a ps/2 device personally, but I'd believe it could happen. It almost certainly shouldn't, though.



This is about PS/2 mouse polling though. PS/2 keyboards are common in the enthusiast space - I have one, for example. But PS/2 mice have been dead a long time since USB polling rates are more than sufficient to exceed the capabilities of PS/2 mice. There is no mechanical benefit to them at all, and thus using the universal interface is almost always the reasonable choice.

And in addition to that you can attach a hub to a USB port so you can easily have 8 USB devices (4 per port) in the same space as one ps/2 device

[Petteri]

I've never seen a notebook advertising a trackpad as a ps/2 device personally, but I'd believe it could happen. It almost certainly shouldn't, though.

That is interesting because I have never seen a notebook trackpad which wasn't a PS/2 device. Even my not-too-old Toshiba ultrabook has touchpad with PS/2 interface (AlpsPS/2).