[Coco] disable super extended basic

[William Astle]

On 2016-01-28 10:09, Robert Hermanek wrote:
> Is it possible to "disable" super extended basic on a coco3?  If I
> understand the boot process correctly, the original unmodified basic and
> extended basic code is in ROM, and the boot process automatically
> executes the "super" extended basic code in the $E000+ range, and this
> code "patches" the originally loaded extended basic ROM image to
> integrate the super extended functionality.
>
> Well ok.  But I was thinking the other day it would be nice to have
> basic, and extended basic, and HDB-DOS (in my case) all loaded up as per
> normal, but then detach super-extended basic and get it out of there...
> it would be nice to be able to build my own ML code that does clever
> things with the coco3 hardware, while leaving the basic interpreter
> intact.... and if I'm not using super extended basic commands, the $E000
> memory page would be a great place to put it.

As long as you are not using any SECB features, you can disable SECB.

There are two easy ways to do it. First, you can simply drop into ROM 
mode. However, that means you can't use the upper 32K of RAM in the 
machine since accessing that would access the ROM.

Alternatively, you can do a simple ROM/RAM copy, the same as you would 
do on a 64K coco2. That will copy the ROMs over *without* the fancy 
patching and other gimmicks done at startup. Doing it this way would 
mean you have no problems with RAM access and can actually use the upper 
8K of RAM for some purpose. (24K would be used for the ROM copies.)