Open GoogleCodeExporter opened 9 years ago
I have updated hs.tap utility to allow one to edit the parameters. It should be
possible to generate all sorts of wonderful sounds but currently the shift
register
for mode 100 does not appear to be relying on T2 low order timeouts to shift.
Original comment by Jonathan...@gmail.com
on 18 Feb 2010 at 10:37
Attachments:
I can't seem to make it do anything at all. Certainly timer 2 is never written
to.
Original comment by p...@petergordon.org.uk
on 2 Mar 2010 at 8:42
I/We need to try this prog on a Real Oric
If my understanding is correct a shift occurs either when a value is stored in
SR or
when Timer 2 latches the low order byte.
Original comment by Jonathan...@gmail.com
on 3 Mar 2010 at 10:24
What i mean is, the program itself doesn't seem to work at all. I press space,
but no
registers seem to ever get written to at all.
Original comment by p...@petergordon.org.uk
on 3 Mar 2010 at 1:38
BTW, when you say:
"Timer 2 latches the low order byte"
you seem to think that timer 2 will expire, then reload from the latch. I find
no
evidence from the datasheets i have to hand that this is the case. As far as I
can
tell, timer 2 *always* decrements through zero and carries on from $FFFF.
This is why my current "shift out under T2 control" shifts at a rate determined
by
the timer 2 latch value, and doesn't use the actual timer 2 counter itself. I
don't
have an easy way to test a real VIA at this time, so if you could prove or
disprove
this, i'd be grateful ;-)
Original comment by p...@petergordon.org.uk
on 3 Mar 2010 at 1:44
Err... yes... so to be clear, my implementation currently does the following:
* Writes to the T2 low order latch set the shifting rate, but does not trigger
a new
shift operation
* A read or write of the SR triggers the beginning of the shift operation
* A shift operation occurs once every "timer 2 latch value" cycles
This is how I understand the datasheet.
Original comment by p...@petergordon.org.uk
on 3 Mar 2010 at 1:46
It seems that the wikipedia article on the 6522 has been updated and is more
accurate regards the 6522 Shift Register bug. Is it more acurate for you to
more accurately emulate the Shift register? :P
Original comment by Jonathan...@gmail.com
on 21 Jun 2010 at 1:00
It looks like it does, but i'd have to go back and re-read the datasheet as
i've pretty much totally forgotten how the VIA works at that level of detail :)
None of this changes any of what I said above, btw.
Original comment by p...@petergordon.org.uk
on 21 Jun 2010 at 2:48
Ok, I re-read all the above earlier and i realise i avoided many of your
questions, apologies. i'll need to take a look at hs.tap
Original comment by Jonathan...@gmail.com
on 21 Jun 2010 at 3:55
Original issue reported on code.google.com by
Jonathan...@gmail.com
on 17 Feb 2010 at 9:51Attachments: