[Coco] The DOS command

[RETRO Innovations]

On 11/7/2019 7:06 PM, Phill Harvey-Smith wrote:
> On 08/11/2019 00:57, RETRO Innovations wrote:
>> is there a comparable story about self starting carts that do NOT tie 
>> CART to Q on the cart port? I tried to explain that such a thing must 
>> be happening for things like CoCoSDC and the FD controller, as they 
>> need CART IRQ available, but they autostart...  I assume it must be a 
>> special set of values in the ROM on the cart.
>
> First two charcaters of the ROM must be 'DK' and the cart is entered 
> at $C002.
>
> From the Dragon ROM, I'm assuming the CoCo would be much the same :
>
>     LDX     #$444B        ; Check for 'DK' flag for DOS cart
>     CMPX    $C000
>         LBEQ    $C002        ; yes, found, jump to Dos init
>
>         ANDCC   #$AF        ; Enable IRQ and FIRQ
> At this point if FIRQ is tied to Q, then the FIRQ vector will be 
> followed, which ultimately enters the cart at $C000
>
> It should also be noted that if a 'DOS' cart is entered at $C002, the 
> IRQ and FIRQ are still disabled to give the DOS rom a chance to change 
> the vectors, and clear any interrupt sources it may be using before 
> enabling them.
>
> I do know of at least one cart for the Dragon that enters the code at 
> $C002 that is not a DOS cart, namely Compusense's Edit+.
>
> Cheers.
>
> Phill.
>
Thanks so much.  Archiving.

I wonder what DK refers to? "Drive Kode", "Drive Kickstart"... :-)


Jim

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