Re: [Qemu-devel] [PATCH] fdc: fix MAX_FD probelm

[Natalia Portillo]

There has never been autodetection.

I can check for it if you want in IBM PC original BIOS' source code.

When the user tried to access a drive, simply the BIOS said that the  
drive does not answer.

Newer BIOS started to do a seek to check if drive is present and  
working, on seek fail, drive fails.

But it is hardcoded, if you put in the BIOS configuration that there  
is a second drive and there is none, the BIOS will indeed do a seek,  
fail, indicate the drive fails, but inform the operating system, there  
is a second drive in the system.

You can just check in any modern BIOS, disconnect any floppy drive,  
select in BIOS you have a 5.25" drive (or the oldest it can) and A:  
will appear on Windows showing you exactly that drive.

El 13/09/2009, a las 16:42, TAKEDA, toshiya escribió:

> Dear Stuart and members,
>
> > On Sun, Sep 13, 2009 at 07:07:12PM +0900, 武田 俊也 wrote:
> > > I added "connected" t fdrive_t to show physical drive is connected  
> > > or not
> > > and it is initialized in fdctrl_connect_drives().
> > >
> > > This is new patch.
> >
> > Neat. :-)
> >
> > I'm still slightly concerned that for machines with  
> > MAX_PHYSICAL_DRIVES
> > set to 2, guests would see drives 2 and 3 as present, but with no  
> > disk
> > inserted.  Previously, though, I expect they would have been  
> > mirrors of
> > drives 0 and 1, which is obviously worse!
>
> FD_DOR_SELMASK is not affected by MAX_PHYSICAL_DRIVES and is fixed  
> to 3,
> so I think drive 2 and 3 are not recognized as the mirror of 0 and 1.
>
> Because MAX_PHYSICAL_DRIVES == 2, drives[2 or 3]->bs is always null,
> but it may be same as drives[0 or 1] with no diskette inserted.
>
> I don't know how PC/AT BIOS detects the physical drive existance.
> In PC-98x1 family case, BIOS executes 4 recalib commands for each  
> drives
> and check the results of sence interrupt status commands to detect
> which drives are connected and power-on.
> (PC-98 BIOS also check the results of sence drive status command to
> detect the diskette is inserted.)
>
> If it is similar to PC/AT case, it is the problem of fdc commands.
> Now fdrive_t has the flag "connected", so we needed to fix
> the sence interrupt status command that it checks "connected" flag
> and changes the results.
> (We may need to fix other commands in the same way.)
> But I need time to investigate the real fdc behaviors on my pc.
>
> Well, I also think it is better the user can select the physical drive
> number, not only 2 but 0, 1 and 3.
> But it will require the large scale patch, for example the block and
> qemu option commands.
>
> In this patch, I hope I fix only the mirror problem of drive 2 and 3,
> and add "connect" flag that will help specifying several physical
> drive number in future.
> And I hope other 2 itmes are for another patch.
>
> If this patch is acceptable for commit, I will reimplement PC-09 patch
> based on it and in this time I hope I can fix the sence interrupt  
> status.
>
> Thanks,
> TAKEDA, toshiya
>
> > Cheers,
> > --
> > Stuart Brady