Date   : Sat, 20 Jun 2009 01:48:57 +0200
From   : kortink@... (John Kortink)
Subject: One ROM disabling all others on Bootup

On Fri, 19 Jun 2009 23:56:17 +0100, "Mark Haysman"
<jumbos.bazzar@...> wrote:

>[...]
>
>Working in a Model B, I need to be able to have the facility in a ROM, when 
>necessary, to disable, and keep disabled, all other ROMs except itself and 
>Basic, even through a <CTRL><BREAK>. I have a private memory flag outside 
>normal memory that keeps a tag on if this is needed or not.
>
>[...]
>
>However, this doesn't work for filing systems that are in a higher priority 
>socket. I've tried claiming the &03 call, returning &00 in the Accumulator, 
>but that doesn't seem to work.
>
>Is there any magic way of doing this reliably, so that I can keep this one 
>ROM, and Basic as the only active ROMs in the System, without any filing 
>systems claiming their workspace?

Place a JMP <your ROM byte whacking code>@&287.
It gets called after the ROM bytes are determined,
and before the first service call goes round (which
is &FF if the Tube is present, else &01).

Otherwise, service call &01 is your first hookpoint,
but of course there's no guarantee that no ROM has
claimed any absolute workspace once you're up.


John Kortink

-- 

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