Reading Polymorphic hard sectored double density disk
dkelvey at hotmail.com
Sat Feb 16 23:04:12 CST 2008
I made good progress today. I got the programmer working again.
I'm now doing 2716s on the PB-10 again.
I blew some more test code and also figured what the problem was
with the controller.
Previously, I'd gotten the frequencies change in the crystal and
PLL circuits. I got to the point that it appeared to be reading the
disk into the USART chip but not getting data into the dual ported
RAM. It was still erroring on the header. I wrote code to ignore
the header and tried that. It still seemed to be missing the header
This is when the programmer decided to cause problems.
While waiting to get parts I realized what the problem
was with the controller.
I was running everything from the memory window in the
Poly88s monitor. Every time it updates a single byte,
it rereads a large block of memory to put into the display.
I was pointing to the RAM that was double ported and
this stole cycles from the controllers time. This caused
missed bytes from the USART.
I wrote some simple code in another area of memory and
used that to initiate the read command. It was then reading
the header and data without missing any of the header or
I expect I'll soon make greater progress.
I need to delay some before reading the double ported RAM
or the controller will miss the first few bytes.
I need to write my serial transfer and finish the code for
reading the sectors.
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