[Coco] Is the 6309 worth it?

[Robert Gault]

L. Curtis Boyle wrote:
><snip>
>      The biggest hurdle of using a 6309 is if you use RS-DOS almost  
> exclusively... there are only a few programs that properly use it (Sock  
> Master's MOD player, Roger's Spyder Hyper & Projector III, and maybe a few  
> others. I believe Robert Gault came out with some patches for the Coco 3  
> only to allow RS-DOS to run in native mode, getting you that 12-15% speed  
> increase, and I know Sock Master had some patches for screen scrolling as  
> well, that helped a lot, but not much more than that.
> 

There is no reason why Disk Basic could not be made to run in 6309 
native mode. The main problem is providing backwards compatibility for 
all Disk Basic programs.

The gotcha with native mode is the difference in the size of the stack 
during interrupts. The Disk Basic NMI service routine must be patched. 
There may be others but I can't think of any. Since many programs 
contain their own disk routines and don't use the ROMs, each of these 
programs would need patching to run in 6309 native mode.

In creating 6309 patches for the ROMs and writing EDTASM6309, I chose 
compatibility over speed and stuck with the 6309 emulation mode.

The best way in Disk Basic to use the 6309 native mode (in my opinion) 
is to incorporate switching into programs. The author could run in 6309 
native mode, switch as needed for disk I/O to emulation mode, and exit 
the program in emulation mode. This takes just several bytes of code so 
is not an inconvenience. It is completely analogous to programs that 
switched to the full fast mode on the Coco1. It works fine (even if you 
loose video) as long as you slow down after doing your task.