Re: Accessing large Hard disks
- From: "Benjamin David Lunt" <zfysz@xxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: 31 Oct 2009 21:24:03 GMT
"Ruud" <Ruud.Baltissen@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:4aec5cf6$0$5670$9a6e19ea@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
Having read BGB's answer it seems I have to go for LBA in PIO mode.
In the mean while I changed my mind:
1) Running the program from EPROM sounds nice but undoable for people
not having such a card. And, BLUSH, I forgot that I cannot equip my
laptop with such a car either.
2) Testing with the floppy sounds nice handling real data means
accessing the hard disk anyway.
So I decided to start directly from the hard disk.
But while doing some tests with the floppy, I ran into some trouble:
things went wrong when saving or loading more then 32 sectors to/from
the floppy disk. In that case I gaot error #9, meaning: DMA out of the
64 KB boundary. But 32 sectors =E0 512 bytes is only 16 KB. Did I miss
something ???
Any info is appreciated!
It really doesn't matter that it is only 16 KB. The error is that
one of those bytes crossed a physical 64k boundary. You must make
sure that your 16k is within a physical 64k block.
For example, if I were to transfer only 16 bytes, the following
would still give the error:
mov es,00FFFh
mov bx,0000Fh
mov cx,10h
Since the physical address is ((0FFFh<<4)+000Fh) or 0x0FFFFh.
The first byte would still be in the first 64k of RAM, but as soon
as it tried to transfer the second byte, it would error since
0FFFFh + 1 is now 10000h (65536d), in the second 64k of RAM.
Do you see what it means by 64k boundary?
Ben
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