18 Nov
2005
18 Nov
'05
11:35 a.m.
"Chuck Guzis" wrote:
On 11/17/2005 at 8:47 PM Brad Parker wrote:
Ah. I'd love to see the schematics - are they on the web?
I'm confused (sorry). Are you trying to build
a PCI board with a Pertec
interface?
Yes, basically--and one that will handle arbitrarily long records (i.e.
much greater than 64K). I've built an ISA Pertec adapter that will do
this, but it's too slow to keep up with a faster drive. I've also built a
PCI version of a sort that uses a PCI card with 2 82C55's on it, but again,
it's not quite fast enough. I was under the impression that the qbus cards had the
64K record size
limitation.
Probably so.
What's the maximum block size?
If you don't mind discussing it, I'd be interesting to know why you want
such big blocks - are the tapes 'preexisting' and you just want to read
them, or do you want to create tapes with huge blocks? (if so, why?)
Also, what's the aggregate data rate in bytes/second? I assume you want
to 'stream' so the drives don't rock back and forth.
You might be able to get by with one of those little SAM7's cpu's. They
have a usb interface but it's only usb 1.1. Not much interal ram,
however (<64k). Now that I think about it I'm skeptical since you'd
have to buffer from the tape and feed out 64 byte bulk packets - pretty
tight timing wise.
I suspect the $200 pci bus solution might be your best bet cost wise,
but I would think you'd have to have at least a little fifo to buffer as
you arbitrate and burst onto the pci bus. Depending on the cpld/fpga
you might be able to use internal ram and do it all with some simple
verilog/vhdl.
On the read side I think I'd just double buffer and have two registers
in the pci card, one for each buffer, and then status & count for each
one. Very simple. Writing should be the same, again, with the fifo's
which allow you the dma to run ahead.
-brad