Messages in this thread | | | Date | Thu, 14 Mar 2002 13:26:37 -0800 (PST) | From | John Heil <> | Subject | Re: IO delay, port 0x80, and BIOS POST codes |
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On Thu, 14 Mar 2002, Pedro M. Rodrigues wrote:
> Date: Thu, 14 Mar 2002 22:19:23 +0100 > From: Pedro M. Rodrigues <pmanuel@myrealbox.com> > To: John Heil <kerndev@sc-software.com>, root@chaos.analogic.com > Cc: Linus Torvalds <torvalds@transmeta.com>, linux-kernel@vger.kernel.org, > Martin Wilck <Martin.Wilck@fujitsu-siemens.com> > Subject: Re: IO delay, port 0x80, and BIOS POST codes > > > This piece of code is taken from an old Minix source code tree, the file being > boothead.s . Notice the port 0xED usage and the comment. > > > ! Enable (ah = 0xDF) or disable (ah = 0xDD) the A20 address line. > gate_A20: > call kb_wait > movb al, #0xD1 ! Tell keyboard that a command is coming > outb 0x64 > call kb_wait > movb al, ah ! Enable or disable code > outb 0x60 > call kb_wait > > > mov ax, #25 ! 25 microsec delay for slow keyboard chip > 0: out 0xED ! Write to an unused port (1us) > dec ax > jne 0b > > ret > kb_wait: > inb 0x64 > testb al, #0x02 ! Keyboard input buffer full? > jnz kb_wait ! If so, wait > ret > > > > /Pedro > > On 14 Mar 2002 at 16:03, Richard B. Johnson wrote: > > > > > > > Well I can see why he's an EX-Phoenix BIOS developer. A port at 0xed > > does not exist on any standard or known non-standard Intel/PC/AT > > compatible. > > > > Remember DOS debug? > > > > C:\>debug > > > > -i ed > > FF > > -o ed aa > > -i ed > > FF > > -o ed 55 > > -i ed > > FF > > -q > > > > > > This is not a DOS emulation. This is a real-mode boot where any ports > > will be visible. If you used it with success, it means that you didn't > > need the I/O delay of writing to a real port. Instead you got the few > > hundred nanoseconds of delay you get by writing to nowhere. > > > > Cheers, > > Dick Johnson > >
We did not want the I/O delay based on the port itself. We specifically wanted an unused port, and avoid the 0x80 conflict.
Perhaps this should be a kernel hacking/debug option, due to the difference in environments and needs.
Johnh
- ----------------------------------------------------------------- John Heil South Coast Software Custom systems software for UNIX and IBM MVS mainframes 1-714-774-6952 johnhscs@sc-software.com http://www.sc-software.com -----------------------------------------------------------------
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