Okay my bad it is ATA-1 but even that does not explain the bit.
only that section 7.2.6 top of page 14 (index numbers) defines it to be
set to 1 with out a reason.
This this is a pre-ATA thing back in IDE.
If you really want to know the answer I can go dig it up, but later.
Cheers,
Andre Hedrick
ASL Kernel Development
Linux ATA Development
-----------------------------------------------------------------------------
ASL, Inc. Toll free: 1-877-ASL-3535
1757 Houret Court Fax: 1-408-941-2071
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On Fri, 29 Jun 2001, Gunther Mayer wrote:
> Andre Hedrick wrote:
> >
> > That is a legacy bit from ATA-2 but it is one of those things you can not
> > get rid of :-( even thou things are obsoleted, they are not retired.
> > This means that you have to go back into the past to see how it was used,
> > silly! I hope you agree to that point.
>
> No,
> in ANSI X3.279-1996, "AT Attachment Interface with Extensions (ATA-2)",
> Approved September 11, 1996 , control register bit 3-7 are reserved.
>
> However ANSI X3.221-1994, "AT Attachment Interface for Disk Drives",
> Approved May 12, 1994, bit3 is "1" and bits 4-7 are "x". No further explanation.
>
> How far back must we go, to get the sense ?
>
> >
> > This is the drive->ctrl register pointer.
> >
> > outp(drive->ctl|0x02, IDE_CONTROL_REG);
> >
> > typedef union {
> > unsigned all : 8; /* all of the bits together */
> > struct {
> > unsigned bit0 : 1;
> > unsigned nIEN : 1; /* device INTRQ to host */
> > unsigned SRST : 1; /* host soft reset bit */
> > unsigned bit3 : 1; /* ATA-2 thingy */
> > unsigned reserved456 : 3;
> > unsigned HOB : 1; /* 48-bit address ordering */
> > } b;
> > } control_t;
> >
> > This is a new struct that is to be added for 48-bit addressing and it will
> > reflect drive->ctl soon. I have not decided how to use it best or at all,
> > but it has meaning and once I add-in the real def of bit3 then I will not
> > need to look it up again.
>
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