Re: Cursor#18 HI-RES

From: Rhialto <rhialto_at_falu.nl>
Date: Thu, 30 Jul 2020 14:16:24 +0200
Message-ID: <20200730121624.GG22551_at_falu.nl>
I adjusted the timing in VICE for CRTC-less PETS, and now it is close
enough that the HI-RES program actually shows something interesting.

If it shows exactly what the author intended, I don't know.
I do know that it flickers, which I also remember seeing on real
hardware. There is at least a part of the CURSOR logo there.

The current implementation in VICE triggers the retrace interrupt
immediately after the last visible scanline has been drawn, if I
interpret things correctly.

It is possible that hardware had a bit of extra delay first. What I've
seen in the VICE monitor may suggest that the program runs a bit ahead
of schedule, but that depends on how one should interpret concepts as
"current scanline" in a line-based (not cycle based) emulation.

Is there some documentation where one can find exact timing of the IRQ
trigger?

I did get the number of cycles per line to 64 (the HI-RES program
assumes this) and the refresh frequency at almost exactly 60.000 Hz. In
fact, it should be a tad higher, since in the New ROMs there is a timing
fix that delays counting of TI by 1/623:

        0099-009A               Jiffy clock correction: 623rd 1/60 sec
                                does not increment time

-Olaf.
-- 
Olaf 'Rhialto' Seibert -- rhialto at falu dot nl
___  Anyone who is capable of getting themselves made President should on
\X/  no account be allowed to do the job.       --Douglas Adams, "THGTTG"


Received on 2020-07-30 15:00:03

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