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FreeDOS on SBC188 (Announce)

posted by GizMo79, 15.09.2020, 21:19

> > > Next try the following:
> > >
> > > 1. Boot into the debugger.
> > >
> > > 2. boot protocol chain b12test.bin
> > >
> > > 3. tp fffff while cs != 1FE0
> >
> > [image]
>
> As expected.
>
> > > 6. d ds:si - 10 length 20
> > >
> > > 7. Again show us what is visible.
> >
> > [image]
>
> This confirms that the memory was not corrupted: The dot is still in memory
> after the call instruction where it belongs.
>
> > > 4. tp fffff while cs == 1FE0 && (ip != 7D41 || al == 2E)
> > > silent
> > >
> > > 5. Show us what is visible after the prior step.
> >
> > [image]
>
> Ah, now everything is clear. The SBC188 ROM-BIOS that you use appears to
> modify the value in the al register when called for interrupt
> 10h service 0Eh and the cursor is at the end of the line. In that case it
> returns with al equal to 0Ah (the Line Feed codepoint). The
> modern FAT12/FAT16 FreeDOS boot sector loader expects the register to
> remain unchanged, so that
> it
> can check whether it finished displaying.
>
> On your hard disk either you're using the (CHS) FAT32 loader, or it might
> be the case that you're using the FAT16 loader but it doesn't display as
> many dots as needed to fill the line width. If you have a cluster size
> larger than 1 sector (512 bytes), then the sector reading code will only
> display one dot per cluster. It will
> loop
> to read_next for the subsequent sectors in the cluster, which doesn't
> display another dot.
>
> If you're already in contact with the maintainers of the SBC188 board's
> firmware, can you please point them to this? The int 10.0E service is
> expected to preserve the contents of the al register. I will
> prepare a patch for the FreeDOS boot sector loader regardless, but it is
> better to fix the bug on both sides, so that current FreeDOS loaders will
> also work on this board after a ROM-BIOS update.
I use FAT16 for compact flash

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