[Coco] DriveWire on EPROM ?

[William Astle]

It is possible to merge HDBDOS into the internal ROM on the coco3. 
However, doing so requires substantial changes to the bootup code. The 
bare minimum code required to make it work does fit in the left over 
space above the SECB ROM code, though. I did a proof of concept test of 
such a setup using MESS a while back.

The proof of concept required no modifications to the HDBDOS ROM code. 
It just required moving the internal bootup code that currently resides 
at C000 to FAxx above the SECB ROM code. The remainder of the boot 
sequence remained the same including all the patching, ROM/RAM copying, 
etc., with the exception that it needs to check the internal ROM for 
disk basic. It's actually not terribly difficult though you do have to 
rip out the easter egg, of course. (That also requires updating the 
reset routine stub at 8C1B to jump to the right place, but otherwise the 
rest of the ROM needs no changes.)

On 2016-01-18 13:59, Arthur Flexser wrote:
> The original version of that internal ROM is coded so as to include booting
> up the Color Basic and Extended Basic images that the chip contains, plus
> booting up Disk Basic if it is present in the disk controller.
>
> To do more would require additional coding.  You couldn't just "pop in"
> some code that was written to be booted via inclusion in the Disk Basic
> chip.
>
> Art
>
> On Mon, Jan 18, 2016 at 3:50 PM, Jason M <oleribus at gmail.com> wrote:
>
>> perhaps I'm not using the right terms ... my chip is removable ... the chip
>> that was in there had a custom image that my company had developed back in
>> the day ...
>>
>> a co-worker used his old EPROM writer to put color basic 2 image on a
>> M27C256B chip, I popped it in the coco and it booted right up ... that was
>> a 32K rom.
>>
>> On Mon, Jan 18, 2016 at 3:38 PM, Arthur Flexser <flexser at fiu.edu> wrote:
>>
>>> A significant problem with replacing the internal ROM chip with an EPROM
>> is
>>> that the chip is soldered in. For that reason, no one to my knowledge has
>>> bothered to explore putting enhancements in that chip rather than in the
>>> disk controller one.  The internal chip does have enough free space for
>>> substantial additional code.  The Mugateers image that appears when you
>>> press control-alt-reset takes 6K in itself and could be replaced by code.
>>>
>>> However, you'd have to write some specialized routines to make use of
>> such
>>> code, whereas putting it in the disk controller uses the bootup sequence
>>> already built into Basic.
>>>
>>> Art
>>>
>>> On Mon, Jan 18, 2016 at 3:13 PM, Jason M <oleribus at gmail.com> wrote:
>>>
>>>> Is there a way to load HDB-DOS or DW3DOS from the EPROM on the main
>>> board ?
>>>> Which I believe is a 32K chip. The rom images I'm finding look like
>> they
>>>> are 8K and are for a Disk Controler EPROM ?
>>>>
>>>> Thanks,
>>>> JasonM
>>>>
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>>>
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>>
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>