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Is it technically possible to write a kernel module to physically connect a PS/2 keyboard to a USB port using a passive converter? If not, why?

(If I simply wanted my keyboard to work I would buy an active adapter, but the purpose of this question is to learn something)

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  • Looks like an XY problem. Do you want to connect a PS/2 device to a USB port physically? Or do you want to create a virtual USB device that actually corresponds to your PS/2 device which would be connected to a true PS/2 port? Please add proper details to your question.
    – xhienne
    Aug 17, 2017 at 13:14
  • I want to physically connect a keyboard with a ps/2 plug to a usb-port with a non-active converter. I updated the question.
    – Louic
    Aug 17, 2017 at 13:22

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No.

No USB standard implements backwards compatibility with PS/2. PS/2 mice which predate USB do not contain time-travelled USB descriptors. Nor can an arbitrary USB port be accessed as a GPIO.

USB descriptors: https://blog.digital-scurf.org/posts/stm32-and-rtfm/

https://en.wikipedia.org/wiki/Gpio & https://en.wikipedia.org/wiki/Bit_banging

(Wiki links aren't going to be great, but the introductions here should give the idea).

Converting the opposite way round, passive USB to PS/2 converters require USB support in the USB input device, and recent USB devices don't bother with it: https://en.wikipedia.org/wiki/PS/2_port#Conversion_between_PS.2F2_and_USB

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  • This is wrong. Enabling "legacy usb" in BIOS let's you use passive USB/PS2 (pin to pin) converters. And they work on windows. No usb logic in them.
    – Zibri
    Mar 13, 2023 at 21:08
  • Congratulations. It would indeed be technically possible to write a kernel module that allows that to work. In fact you could write it in any language! Python would be a good example of a language where this program can be written in zero bytes. :-P.
    – sourcejedi
    Mar 13, 2023 at 22:44
  • Usually when I've seen "legacy USB" in BIOS, it's to allow using a USB device in an OS which only supports PS/2. Did you check that disabling "legacy USB" actually stops this alleged antique wonder from working? You might find the option is not actually necessary for this.
    – sourcejedi
    Mar 13, 2023 at 22:49
  • Pictures would also be very interesting :-).
    – sourcejedi
    Mar 13, 2023 at 22:51
  • 5kw.dk/Hobby/electronics/connectors/usb_and_ps2.jpg
    – Zibri
    May 5, 2023 at 15:25
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Enabling "legacy usb" in BIOS let's you use passive USB/PS2 (pin to pin) converters. And they work on windows.

I've never tried with linux though.

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