[Coco] [Color Computer] OS-9 Question, GCC stuff

jdaggett at gate.net jdaggett at gate.net
Fri Jul 22 18:53:25 EDT 2005


While the 6809 does allow the direct page to sit in any 256 byte 
block of memory, with OS9 I would be reluctant to allow user 
programs to alter the DP register value from that which the OS sets. 

Changing the DP register contents on the fly and not resetting them 
can cause the OS to do some mighty funny things. One to say at 
least is crash.

In embedded situations this can be a nice feature to move the DP 
memory within the 64K memeory map. Even then, one has to be 
sure that all su broutines and interrupt service routines know of the 


On 22 Jul 2005 at 20:35, James Diffendaffer wrote:

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From:           	"James Diffendaffer" 
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Date sent:      	Fri, 22 Jul 2005 20:35:56 -0000
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9 Question, GCC stuff
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> What limitations does OS-9 place on the use of page 0 and DP usage by
> programs?  I'm guessing Page 0 is reserved for the OS but the DP would
> be ok to use for a user program... but I don't have any OS-9 docs so I
> wan't to make sure.  
> GCC 68HC11 places it's software registers on page 0 for fast access. I
> figured I could place the soft registers in the GCC startup code or at
> the start of the data segment and point the DP there to access them. 
> Without that GCC's code will be significantly slower.
> I've gone throught the instruction sets of the 09 and HC11.  The
> differences are managable so far.  The remaining issue is whether or
> not the compiler uses address modes that the 09 doesn't support for
> the same instructions. 
> To resolve the problems I was having with Cygwin I had to delete my
> entire install and install from a different mirror.  Once I did that
> the GCC configuration and make seemed to work great.  Something was
> wrong with a file on the mirror I had been using and it was causing
> problems with my install.  
> The make took a while (I walked away after 20 minutes) to make the
> entire GCC project on my 2.4GHz system the first time so anyone
> planning to build everything should expect to start it and check back
> later.
> Brought to you by the 6809, the 6803 and their cousins! 
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