[Coco] GIME questions

[jdaggett at gate.net]

David

I gather this is your PIC emmulation of a 6809 processor. 

I gather you are not real familiar with 6809 assembly or the instruction set?

Could the problem be in your emmulation code not doing an equivalent/compatible 
of the 6809 instruction set?

If your are already stepping through the standard internal COCO3 rom then most 
likely what is happening is that you  may have some error in the emulation of the 
6809 instruction set. 

james


On 16 Aug 2004 at 9:19, David Gacke wrote:

From:           	"David Gacke" <dgacke at ektarion.com>
To:             	"'CoCoList for Color Computer Enthusiasts'" 
<coco at maltedmedia.com>
Subject:        	RE: [Coco] GIME questions
Date sent:      	Mon, 16 Aug 2004 09:19:06 -0500
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> Hi Robert,
> 
> Sorry it wasn't clear. So far, you are correct though.  I am stepping
> thru the code with my dsPIC CPU that I'm coding, not a 6809 or 6309
> and am trying to figure out what I broke.
> 
> To try and put it simply, by looking at that startup code, what would
> make a shadow copy of what is located at C000 appear at 4000.
> 
> Which GIME registers bits would I set if I wanted to do this
> intentionally?
> 
> I've stepped thru the code and am not finding a broken instruction. I
> want to fully understand how to reproduce this intentionally, maybe
> then I can figure out what is going wrong.
> 
> This one has me a little bit stumped, especially since I've never
> really done assembly on the CoCo (lots of other systems though), and
> I've never twiddled the bits on the GIME before.
> 
> Thanks very much for the assistance.
> 
> Dave
> 
> 
> -----Original Message-----
> From: coco-bounces at maltedmedia.com
> [mailto:coco-bounces at maltedmedia.com] On Behalf Of Robert Gault Sent:
> Monday, August 16, 2004 8:42 AM To: CoCoList for Color Computer
> Enthusiasts Subject: Re: [Coco] GIME questions
> 
> Robert Gault wrote:
> > David Gacke wrote:
> > 
> >> Hi Guys,
> >>
> >> I've got a GIME problem and I'm not sure what's going wrong. For
> >> some reason, "I think", it's not mapping RAM correctly.
> >>
> >> I'm stepping thru the startup ROM code on my CoCo 3, which matches
> the
> >> version I'm looking at in MESS. Just a plain old CoCo3 ROM.
> >>
> >> Anyway, there's a write to $FF90 with a value of 0x0A, then there's
> some
> >> startup code to set palette registers to all green, then there's
> >> some code to start copying code from $C03F to $4000.
> >>
> >> This is where I get into trouble. Immediately after writing the
> >> first word, with the STD, Y++ instruction, I read back the
> >> contents. The address I'm reading from is $4000 and I'm seeing the
> >> same data that
> is
> >> at $C000.
> > 
> > 
> 
> OK just so everyone is on the same page, the code in question is from
> the 32K ROM in a Coco3 and is as follows:
> 
>   lda #Coco+MMUEN+MC3+MC2+MC1
>   sta $$FF90
>   leax begmove,pcr
>   ldy #$4000
> LC02F ldd ,x++
>   ldu ,x++
>   std ,y++
>   stu ,y++
>   cmpx #endmove
>   bcs LC02F
>   jmp $4000
> 
> David asked why when stepping through this code, the contents of $4000
> =
> 
> that of $C000. He may have meant begmove. Regardless, the content at
> $4000 should be RAM and will look like whatever regY contained after
> the
> 
> std ,y++.
> 
> David, would you clarify what your problem is?
> 
> 
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