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[Bug 1895363] Re: borland IDEs double up cursor key presses (need timing
From: |
Thomas Huth |
Subject: |
[Bug 1895363] Re: borland IDEs double up cursor key presses (need timing on PS2 port input) |
Date: |
Wed, 25 Aug 2021 07:15:29 -0000 |
** Changed in: qemu
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1895363
Title:
borland IDEs double up cursor key presses (need timing on PS2 port
input)
Status in QEMU:
Fix Released
Bug description:
Most DOS-era IDEs from Borland (I have tried Borland C++ 2.0, Borland
C++ 3.1 and Turbo Pascal 7.1) exhibit strange responses to the
keyboard. Cursor keys are registered twice, so each press of a cursor
key causes the cursor to move twice. Also the other keys occasionally
are missed or duplicated.
From an internet search, the problem appears to be this. These
programs read the PS2 input register multiple times per incoming byte,
on the assumption that the byte will remain there for at least a few
hundred microseconds, before the next byte (if any) appears there.
qemu treats a read of the register by the guest as an acknowledgement
of the incoming byte and puts the next byte into the register
immediately, thus breaking the programs that expect each successive
byte to stay in place for a while.
The obvious solution is to use a timer to advance through the queued
bytes.
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