28 Dec
2012
28 Dec
'12
6:30 p.m.
On 12/28/2012 05:05 PM, Fred Cisin wrote:
The NEC 765, and presumably all of the
"compatible" alternatives do a
"reset" on seeing the index pulse. That makes many "crowded"
formats,
such as Cromemco, TRS80, etc. difficult to read on PC.
If feasible, PLEASE consider having that overrideable in software, so that
it is possible to read immediately after the index.
Eww! I don't even understand why they would purposely do that. The PLL
either needs a handout or it doesn't. At the moment, my code ignores index
pulses other than to count them so it knows when to give up (even that
bothers me -- I'd rather use a timer than have the FDC totally wedge up
just because the disk's in backwards or whatever). My only plan for using
index pulses was for the "format" cmd.
On Fri, Dec 28, 2012 at 05:37:28PM -0800, Chuck Guzis wrote:
NEC has sort of a "Read Track - read multiple
sectors without looking
at the IDAM" command; it starts after the index and reads subsequent
sectors starting at each DAM. You can have an unreadable IDAM and
still recover the sector data if the DAM is readable.
Other than data recovery, I never got how that's useful. I'm never so
desperate for data that I don't care which sector it came from! Although,
the very weird SCAN commands show that they imagined just such a use.
You also can feed the 765 a "Read Track"
with a phony datalength
specified. The 765 will suck up all of the data after the first DAM
after the index until the transfer count is exhausted. Thus, you get
gaps, AMs, headers, all "in the raw", meaning that the 765 does not
resync during the transfer.
Where was I for this?!?! That sounds very very useful, almost. What value
constitutes "phony"?
Also, consider implementing some of the 82078 added
commands,
particularly "Format and Write" (can make copying go very fast) as
well as the PM functions.
Very nice! I hadn't noticed that one (I've been using the PC8477B data sheet
since that was the chip I used in Rev A).
Personally, I'd do the board as a USB card, given
the difficulty of
finding ISA-equipped motherboards or dealing with the nuances of
PCI/PCIE, etc.
Absolutely. I'm working on that right now (so I'll have a PCB already
whenever XMOS finally releases the XS1-SU01A to mere mortals, which is
supposedly imminent). I just like to be compatible with everything.
There's plenty of software that wants a uPD765, especially if it's for
booting. I never got the point of the PCI Catweasels -- they aren't
compatible with anything (not even each other, or ISA Catweasels) AND they
use expensive hardware to use up a slot whose bandwidth they don't even
need. But then again, at least the cabling stays out of the way.
You should also be aware that Andrew has been testing
prototypes of
an ISA FDC that can use either the I82077AA, PC8477 or DP8473 chips.
Nice! Well I've got a tube of PC8477Bs that I bought when they were
EOLed that I'm not going to be using after all...
John Wilson
D Bit