15 Feb
2021
15 Feb
'21
11:51 a.m.
On Mon, 15 Feb 2021, Mattis Lind via cctalk wrote:
My guess is that the data that follows the sector ID
is some kind of
checksum.
yes. well, sorta. 16 bit CRC
A typical IBM/WD style format has:
a gap
Index Address Mark
a gap (note that WD can use a shorter post index gap than NEC can)
and then, repeated for each sector:
{
a gap
ID Address Mark,
C Cylinder number
H Head number (0,1)
R Sector number
N Sector Length (0:128, 1:256, 2:512, 3:1024)
16 bit CRC of the sector header
a gap
Data Address Mark
Sector data (128, 256, 512, or 1024 bytes. Larger is possible, but unlikely)
16 bit CRC of the data
a gap
}
(This is from memory (error prone?). The WD1791 datasheet should have
more detail, including CRC algorithm?, the specific requirements for the
address marks, and gap contents (write splice, synchronization, etc.))
--
Grumpy Ol' Fred cisin at xenosoft.com