[Coco] 6309 microprocessor project 01-16-2004

[John Collyer]

So far it only exist in my head as a full fledge emulator.
Thanks for the information I'll save the email and use
it as I need when I get to the specific parts you
specified.  If you can remember anything else
it'll be a great help when I begin to tackle
the specific parts you state.  If any thing
I come up with can be easily applied to
the current ver19 coco3x emulator
I'll be sure to apply the change.

John Collyer

----- Original Message ----- 
From: "John Kowalski" <sock at axess.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>;
<coco at maltedmedia.com>
Sent: Friday, January 16, 2004 3:59 PM
Subject: Re: [Coco] 6309 microprocessor project 01-16-2004


> At 02:26 PM 16/01/2004 -0500, John Collyer wrote:
> >6309 microprocessor project.
> >...
> >I was still wondering what the emulator lacks in making the
> >Sockmaster demos work?  Any insights will be appreciated.
>
> Where could I download this emulator to check it out?
>
> Here's a quick list of things that make 'Sockmaster demos' troublesome
> to emulator:
>
> 1) Mid-frame (On-the-fly) palette updates.  This is how some demos,
CoCoMax
>    III and 64 palette color-charts display more than 16 colors on the
screen.
>    Emulating palette updates once per scan line is sufficient as I don't
know
>    of any programs that require mid-scanline palette updating (unless you
want
>    to go *all-the-way* authentic and emulate palette glitches as well :) )
>
> 2) Mid-frame video mode/resolution updates.  Some demos will change the
video
>    mode to different resolutions for different scanlines of the display.
>    (A real CoCo is capable of mid-line video mode changes, but I can think
of
>    only one program that requires it - Dragonfire for the CoCo1/2, which
>    switches between two color sets multiple times per line to display 8
colors
>    in the otherwise 4 color PMODE3 screen.)
>
> 3) Undocumented video resolutions/modes.  Boink demo takes advantage of a
>    video mode that repeats one scanline throughout the whole frame -
>    essentially 320x1 resolution.  This is how the ball bounces up and down
>    while still allowing stationary graphics at the bottom of the screen -
>    the demo switches to 320x1 mode at specific scan lines to 'stretch' one
>    line below and above the ball itself.  Other than offsetting the video
left
>    and right, what you see is technically a stationary graphics screen
>    throughout the demo!
>    Nick's Gate Crasher uses an undocumented video resolution which was/is
not
>    supported by Jeff's emulator.
>
> 4) Mid-frame horizontal offset updates.  (The horizontal smooth scrolling
>    register)  This is used for wavy effects and multi-sectioned scrolling
in
>    some demos.
>    *Mid-frame vertical (or video address updates) do not need to be
emulated
>    because even a real CoCo 3 does not support this.
>
> 5) Exact CPU cycle counts.  Some programs and demos count cycles to
syncronize
>    with the video raster.  The 6809 executes 57 cycles per scan line at
.89Mhz
>    and 114 cycles per scan line at 1.79Mhz.  The video display has 262
scan
>    lines total.
>
> 6) Exact TIMER and interrupt timing.  Some games and programs use
interrupts
>    to syncronize with the video raster.  If the emulated timing is
different
>    from the real CoCo, things in the display can flicker or appear out of
place.
>    Even the minor differences between the 1986 and 1987 versions of the
GIME
>    were enough to break a few games - most notably the 64 color chart in
>    CoCoMax III.   Emulating 1986 GIME timing is preferable.
>
> 7) Undocumented opcodes.  Not very important, but some programs, and the
>    old/original versions of my demos used undocumented opcodes as
half-NOPs,
>    or 1.5 NOPs for timing purposes. (I patched my demos when I found out
the
>    6309 treated these opcodes differently from the 6809.)
>
> 8) ...What else?  There may be a few more things that I've forgotten.
>
>                                          John Kowalski (Sock Master)
>
http://www.axess.com/twilight/sock/
>
>
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