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Re: LBA vs CHS?

On Sat, 18 Nov 2023, Mouse wrote:
But, upon trying to install on it, bootxx_ffsv1 was having trouble
loading /boot.  I've been sprinkling debugging around.  It is
definitely reading the wrong blocks off the CF "disk"...and it appears
that the BIOS call it's using, int 0x13 function 2, is ignoring the
cylinder number.  (I'm doing this with my mutant 5.2, but this is all
about bootxx_ffsv1 code, so, unless bootxx_ffsv1 has been substantially
worked over, I doubt the OS rev matters.)

I don't know about it ignoring the cylinder number, but int 13h function 02h is limited to approximately 8GB (1024 cyl * 256 heads * 63 sectors * 512 bytes), so I'd expect the boot code to use int 13h function 42h for larger disks. I see a biosdisk_extread routine in http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/arch/i386/stand/lib/bios_disk.S?rev=1.18&content-type=text/x-cvsweb-markup&only_with_tag=MAIN so the code exists in 5.2. I haven't looked to see when it's used though. Although I'd also expect function 2 to work for reading below the 1024 cylinder limit (such as your example of cyl 1 head 4 sec 19).

I ran NetBSD on a Soekris net4501, but with an 8GB CF card. I never had any problems with it booting, but I don't know if it ever had to load anything from other than cyl 0. However, it seems likely that it would have... one cylinder is only about 8MB, right? It seems unlikely that the kernel would have always been on the first 8MB of the card.

Name: Dave Huang         |  Mammal, mammal / their names are called /
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