From: Spiro Trikaliotis (trik-news_at_gmx.de)
Date: 2003-11-21 16:18:24
Hello Ruud,
On Fri, Nov 21, 2003 at 03:12:00PM +0100, Baltissen, GJPAA (Ruud) wrote:
>
> Hallo allemaal,
>
> I'm still busy with disassembling the ROM of my PC20-III. The reason
> why I started this work was to find out how I can replace its HD with
> another type. The only thing I can say is that until now it makes no
> sense :( AFAIK it only uses four I/O addresses: 0320h..0323h, not the
> six I expect for a normal IDE-HD. Even stranger is the following code:
The PC20-III is an XT, isn't it?
The XT HDC is a completely other beast than an AT controller.
Ralf Brown's Interrupt List [1] does not give very much information on
this, but at least the following:
PORT 0320-0323 - XT HDC 1 (Hard Disk Controller)
SeeAlso: PORT 01F0h-01F7h
0320 RW data register
0321 -W reset controller
0321 R- read controller hardware status (see #P0574)
0322 R- read DIPswitch setting on XT controller card
0322 -W generate controller-select pulse
0323 -W write pattern to DMA and INT mask register
Bitfields for XT hard disk controller hardware status:
Bit(s) Description (Table P0574)
7-6 always 0
5 logical unit number
4-2 always 0
1 error occurred
0 always 0
So, in effect, there are 6 registers, but these are located on 4
addresses only.
0324-0327 is HDC 2, 0328-032B is HDC 3.
> ; [AA79]
> FillDX322_326 proc near
> push cs
> pop dx
> cmp dh,0FAh ; CS = $FAxx?
> mov dx,322h
> jz loc_AA86 ; yes, ->
>
> add dx,4 ; DX := $0326
> loc_AA86:
> in al,dx ; port 326h
> retn
> FillDX322_326 endp
>
> The value used to fill DX depends on wether CS = 0FA00h or not! The
> only time I know CS is 0FA00h is right after a reset when the PC is
> scanned for "external" ROM with the well known "55 AA" identification
> code. For the rest, I havent the faintest idea. The only thing I can
> think of adding another IDE-interface with its own _same_ ROM which is
> executed on another address.
This seems to be related to initializing a second HDC, too.
I know, this is not that much info, but I wanted to share it
nonetheless. ;-)
Spiro.
[1] http://www-2.cs.cmu.edu/afs/cs.cmu.edu/user/ralf/pub/WWW/files.html
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