[SeaBIOS] Re: Floppy drive configuration

[Eduardo Batalha]

Hi,

I had some old files saved in diskettes that I really needed to see, so I bought a floppy drive and installed it in my coreboot based computer, so, no, It's not a retro project. :)

Regarding the AHCI CDROM issues, I really don't know. I did not have problems with it so I did not look at that code at all.

Going back to the floppy configuration issue I think I need to explain my logic a bit better. 
So... Seabios does not provide us with a fancy interface to configure the floppy drive type. It also does not assume anything. For real hardware, (not qemu,) it is completely dependent on the etc/floppy "file" being present in CBFS. The reason it cannot depend on the cmos value is because when you remove the RTC battery, the CMOS memory gets filled up with random values. coreboot, which runs before seabios has a mechanism to fix this, but ignores the floppy type byte, leaving it with a random value.

My idea below, with my code, is not to use the CMOS value if there are no etc/floppy files but instead to update the cmos value unconditionally whenever etc/floppy files exist.
romfile_loadint returns the second argument if the file does not exist, i.e. 0. so the if condition is correct for the logic I explained above.

On a second thought, I now think the condition "if (type0 || type 1)" should not even exist. The best solution is to have the CMOS_FLOPPY_DRIVE_TYPE always updated on every boot. This way, if there are no etc/floppy files in CBFS the value of the byte would be zero, indicating to the operating system that there are no floppy drives installed.

Cheers,
Ed

On Wednesday, 3 April 2024 at 03:58:40 BST, Petr Cvek  wrote:

Thanks for info,

So I guess yours ICH10 AHCI controller can probably withstand an NULL pointer access in hardware. Unlike my ICH7, which had problems with the same situation, as described here:

https://www.mail-archive.com/[e-mail]/msg12950.html
> > if (type0 || type 1)
> >             rtc_write(CMOS_FLOPPY_DRIVE_TYPE, type0 <<4 | type1);

Oh BTW I was looking how/if the code meanwhile changed and I think it should be:

if (!type0 || !type 1)
        rtc_write(CMOS_FLOPPY_DRIVE_TYPE, type0 <<4 | type1);

or something as in "if none romfile_loadint() set type, use CMOS values".

But on the other hand, if CMOS load is allowed even on a real hardware, then the entire "if (CONFIG_QEMU) .. else ..." block can be optimized out.

BTW^2 I completely forgot to ask. What are you trying to use the floppy for, some retro project?

Best regards,
Petr

Dne 03. 04. 24 v 0:45 Eduardo Batalha napsal(a):
> Hi,
>
> Yes, booting from a SATA DVD drive with the controller configured as AHCI worked fine for me.
>
> Cheers,
> Ed
>
> On Tuesday, 2 April 2024 at 02:19:42 BST, Petr Cvek  wrote:
>
> And I agree ;-)
>
> it worked on Kontron 986LCD, but I don't have time to play with it (and I upgraded to a ryzen board). But actually I'm planing to use all semi-standard CMOS addresses for legacy/retro boards.
>
> BTW does a boot from SATA CD/DVD works for you with seabios? (native IDE CD/DVD on PATA is in question too)
>
> Petr
>
> Dne 02. 04. 24 v 2:59 Eduardo Batalha via SeaBIOS napsal(a):
> > Hi all,
> >
> > I own an ASUS P5Q and had the same problem that Petr Cvek mentioned in his previous emails.
> > I was configuring the floppy type using the the etc/floppy0 value in cbfs but took me quite a while to figure out that why linux was not showing it.
> > I haven't tested it myself yet, but I think the solution to the floppy configuration issue may be to continue using etc/floppyX and change these lines in floppy.c from
> >
> > } else {
> >         u8 type = romfile_loadint("etc/floppy0", 0);
> >         if (type)
> >             addFloppy(0, type);
> >         type = romfile_loadint("etc/floppy1", 0);
> >         if (type)
> >             addFloppy(1, type);
> >     }
> >
> > to
> >
> > } else {
> >         u8 type0 = romfile_loadint("etc/floppy0", 0);
> >         if (type0)
> >             addFloppy(0, type);
> >         u8 type1 = romfile_loadint("etc/floppy1", 0);
> >         if (type1)
> >             addFloppy(1, type1);
> >         if (type0 || type 1)
> >             rtc_write(CMOS_FLOPPY_DRIVE_TYPE, type0 <<4 | type1);
> >     }
> >
> > Quoting from osdev.org :
> > "The first 14 CMOS registers access and control the Real-Time Clock. In fact, the only truly useful registers remaining in CMOS are the Real-Time Clock registers, and register 0x10. All other registers in CMOS are almost entirely obsolete (or are not standardized), and are therefore useless. "
> > So, register 0x10, the floppy drive type, is, conversely, pretty much standardised...
> >
> > Hope this makes sense...
> >
> > Cheers,
> > Ed
> > _______________________________________________
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