18 Nov
2005
18 Nov
'05
1:17 p.m.
"Chuck Guzis" wrote:
On 11/18/2005 at 6:35 AM Brad Parker wrote:
I've just never looked into pertec. Is it ttl? It would be interesting
to see what signals you have to wiggle and how the data goes across.
I'm curious how you figured all that out.
Ah. I'd love to see the schematics - are they
on the web?
No, I did those on pencil and paper. Brutally simple, actually--mostly
receivers and drivers, with latches for holding data and status. My design goal is 1MB blocks. That should cover all
eventualities.
yowza - that's huge. I've never heard of anything writing blocks that
big. Mind if I ask *what* wrote them?
The data rate is about 1.1MB/sec from what I've
been able to determine.
I'd like a bunch of headroom. I'd tried a 16-bit ISA interface (16 bits at
a toss) using PIO, but even with interrupts disabled, I was still losing a
byte now and then, which leads me to suspect that I'm running on the edge.
Interesting. Seems like 1MByte/sec might be an ISA maximum
(http://www.evaluationengineering.com/pctest/articles/e707data.htm)
Using a 32 bit dos extender seems like the way to go - a hard loop. But
once you go to disk all bets are off. I can see how that might end up
being a loose.
I wonder if you just added a fifo to cover the time interrupts might
steal... you could do that in a cpld these days. yea, ok, sorry. I
just had to say it.
The ideal solution would be a double-buffered
bus-mastering DMA setup.
yes, on pci. but I think you'd still need a fifo to cover the arbitration.
If I moved
the whole setup out of the PC box, using a small processor board with a
small hard disk and interfacing via USB or TCP/IP, I'd have a permanent
solution that should work with any host machine. Even with today's
smallest hard disks, I could hold the contents of many tapes on one.
Well that makes sense. If you used something like a BrightStar
IPEngine, you'd have a PPC which will run linux next to a nice FPGA
which has some SRAM next to it. With that you could easily make an
interface which would pull all the data and you could stream it over
ethernet using tcp so you would not loose any data. You shouldn't need
a disk.
But for the same money you could buy a nice pci card with an fpga.
I'd go with an IPEngine style solution but that me :-)
Thanks for letting me kibitz. Very interesting. I'd enjoy hearing more
about the actual pertec interface.
-brad