[Coco] Coco3 warm start...
jdaggett at gate.net
jdaggett at gate.net
Fri Nov 16 13:42:59 EST 2007
On 16 Nov 2007 at 8:29, William Astle wrote:
> Robert Gault wrote:
> > The code at $C000 is hard to follow and the tendency is to make
> > false assumptions.
> > The reset button will cause the CPU to jump to $8C1B which does
> > force the 32k internal ROM mode and jump to $C000. The critical test
> > regards this question is the code at $C0DE-$C0E5. $FFA0 is cleared
> > which removes the normal $38 block and replaces it with the lowest
> > possible block based on available memory. Then $71 is tested for
> > $55. This test will fail for Disk Basic but will pass for OS-9 and
> > some other programs that "know" about the Coco3.
> > Since the above test failed, memory is copied from ROM to RAM and
> > the system switched back to RAM mode.
> Yes, but that test does NOT run unless the test in block $38 fails
> first so if Basic is initialized, it never checks block $00 but rather
> branches into the warm start code. That is to say, $C0DE does not
> execute if the Basic warm start vector is valid. That means on a warm
> start, the ROM is not copied to RAM (which is as it should be).
Remember that the code from $C03F to $C3C is copied to RAM location $x4000 during a
power on sequence and remeains there unless that block is overwritten by other programs.
Then execution is passed to that address. It can be $6400 or $04000 depending on amount
of RAM on board. The initialzation code including cold and warm start is executed in RAM
and not in ROM.
The only ROM code executed in ROM for the Coco3 in the $C000 to $DFFF range is the
code from $C000 to $C03F.
> William Astle
> finger lost at l-w.ca for further information
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