From: Mike Haertel <9fans@ducky.net>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] usb keyboard and mouse?
Date: Wed, 28 Jun 2006 22:31:26 -0700 [thread overview]
Message-ID: <200606290531.k5T5VQ1W000476@ducky.net> (raw)
Er, no. Legacy keyboard emulation is intended to work with any OS,
even if the OS bypasses the BIOS and directly fiddles with the PS/2
hardware. It uses chipset magic to translate "in" and "out"
operations to ports 0x60 and 0x64 (the PS/2 keyboard ports) into
USB operations.
The implementation is chipset dependent. Often what happens is
that the chipset recognizes an I/O request to port 0x60 or 0x64 and
aborts the request with an SMI (system management interrupt). This
is a *very* non-maskable interrupt (more non-maskable than NMI...)
that causes the processor to save pretty much all its register state
in a special memory area, and jump to a handler in the system BIOS.
The BIOS SMI handler examines the saved register state, figures out
what the OS was trying to do, runs a software model of the PS/2
keyboard controller's state, chats with the USB keyboard, formulates
an appropriate response, emulates the I/O instruction the OS was
trying to do, and resumes execution of the OS at the instruction
following the I/O instruction.
Some chipsets might do it directly in hardware rather than using
the SMI+BIOS strategy.
>From: "Artem Letko" <aletko@gmail.com>
>To: "Fans of the OS Plan 9 from Bell Labs" <9fans@cse.psu.edu>
>
>but that's only if your kernel uses BIOS calls, right?
>
>On 6/26/06, geoff@collyer.net <geoff@collyer.net> wrote:
>> Some BIOSes have an option with a name like "enable legacy USB" or
>> "enable USB keyboard" that, if set, will simulate PS2 input from a USB
>> keyboard or mouse.
next reply other threads:[~2006-06-29 5:31 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-06-29 5:31 Mike Haertel [this message]
2006-06-29 8:23 ` Charles Forsyth
2006-06-29 11:55 ` Dan Cross
2006-06-29 15:02 ` Ronald G Minnich
2006-06-29 23:50 ` Charles Forsyth
-- strict thread matches above, loose matches on Subject: below --
2006-06-26 18:50 ISHWAR RATTAN
2006-06-26 19:22 ` Francisco J Ballesteros
2006-06-27 0:19 ` geoff
2006-06-28 15:48 ` Artem Letko
2006-06-28 17:01 ` Francisco J Ballesteros
2006-06-28 23:02 ` C H Forsyth
2006-06-28 23:21 ` Ronald G Minnich
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