autorepeat - How is keyboard auto-repeat implemented on a Windows PC?

Question

I want to be able to intercept (and do arbitrary processing on) auto-repeating key presses on Windows. I'd like to know how keyboard auto-repeat is implemented so that I know what options I have. i.e. can I intercept at the:

• application,
• device driver and/or
• hardware level

?

Update: It looks like auto-repeat is (poorly?) generated at the hardware level and then overridden by device drivers (see here).

Answer 1

To modify or filter behavior, you can intercept keys using a hook:

SetWindowsHookEx using WH_KEYBOARD

The hook procedure receives, among others, the repeat count (due to holding down the key)

Note that the low level keyboard hook (WH_KEYBOARD_LL) does not receive the repeat count.

If all your windows are created in the same trhead, you can use a thread-specific hook, and avoid moving the hook procedure to a DLL.

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I dimly remember that repeat counts are generated by the keyboard itself and the LL hook sends repeated keydown events - I may be mistaken, though. Under DOS, the key repeat rate and time that was set in BIOS or through a BIOS call did return to default values when a DIN or PS/2 keyboard was unplugged and replugged. I am not sure WHY you need to know exactly.