6 May
2007
6 May
'07
12:12 p.m.
Chuck Guzis wrote:
The ones I'm thinking of are 8" systems,
where the drive has separate
outputs for SECTOR and INDEX. There's no compelling reason to pay
attention to INDEX in many applications--and some systems reflect
this.
OK then, looks like I *do* need to read the SA800 docs then...
That was the other thing that I wanted to
mention--that 8" drives
separate sector marks from index marks for you. Most do it with a
couple of one-shots--precision timing isn't terribly important, given
that HS 8" disks had at most 32 sectors. Given that, you may want to
make your determination of index and sector marks optional for those
wishing to make use of the drive capabilities.
That's a good point - if there's a spare pin on the 34-pin connector (and a
bit of spare space in the CPLD) I'll add the relevant logic to it. Pins 4 and
6 on the FDD connector look like fair game - they're listed as "N/C" on my
pinout, but seeing as it's going to be turned into an input, I doubt that
matters much (after all, you can always turn off the external index marker input).
The only thing I'm slightly worried about is if the INDEX output also includes
the half-sector pulse that marks the 'first sector'. That would change how the
drive controller needs to be programmed - if you wanted to read the last
sector on its own, you'd add 1 to the "termination count" (number of times a
termination condition - i.e. the INDEX line - must exist before the R/W
operation is stopped). If the drive masks out the half-sector pulse, you
wouldn't need to add the 1. Again, all of this is configurable in the CPLD;
the hard part is deciding how to integrate all these options into the software
interface and API!
I think I'll spend this evening sorting out the register interface stuff, tie
all the logic together and see if it passes the behavioural simulations. If it
does, I'll start work on the schematics and PCB.
Thanks.
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