Re: [hatari-devel] Small IDE drive image, wrong physical parameters?

[Uwe Seimet <Uwe.Seimet@xxxxxxxxx>]

Hi Thomas,

I see, but in this case in my opinion Hatari should prevent IDE (but not
ACSI, because they work fine) images < 1 MB to be used, because they do
not work and result in errors when relying on the capacity reported for
them.

Take care

Uwe

> Am Sun, 29 May 2016 19:13:16 +0200
> schrieb Uwe Seimet <Uwe.Seimet@xxxxxxxxx>:
> 
> > Hi,
> > 
> > I wonder whether Hatari correctly sets the physical drive parameters
> > of small IDE drives. With an IDE image file size of 524288 bytes the
> > result according to my calculation is 2016 sectors. This is how I
> > calculate: In case LBA is supported I just use the LBA sector count,
> > if LBA is not supported (LBA sector count is 0) I multiply the nubmer
> > of heads, sectors per track and cylinders.
> > 
> > For an image file size of 410009600 bytes the values appear to be
> > correct. Can it be that the values are wrong for the non-LBA case?
> 
> Have a look at the following code in ide.c:
> 
> 	/* if no geometry, use a standard physical disk geometry */
> 	cylinders = nb_sectors / (16 * 63);
> 	if (cylinders > 16383)
> 		cylinders = 16383;
> 	else if (cylinders < 2)
> 		cylinders = 2;
> 	s->cylinders = cylinders;
> 	s->heads = 16;
> 	s->sectors = 63;
> 
> For a file with 524288 bytes, nb_sectors is 524288 / 512 = 1024, so
> cylinders are first calculated to 1. Since 1 is < 2, it is set to 2
> instead. Then you get 2 * 16 * 63 = 2016 sectors instead.
> 
> Not sure why there is a limitation to 2 cylinders, but I guess there is
> a reason for this, current QEMU also still has this code.
> 
> So I think the it likely simply does not make sense to use IDE hard
> disks with a size less than 1 MB ... even the very first IDE hard disk
> already had 10 MB, so this interface was likely never invented for
> something smaller...
> 
>  Thomas
> 
>