Date   : Sun, 29 Nov 2009 22:33:52 +0100
From   : kortink@... (John Kortink)
Subject: Tube - I/O processor memory questions

On Sun, 29 Nov 2009 20:20:10 +0000, Kevin Bracey
<kevin@...> wrote:

>Exactly what memory is available on the I/O processor for a
>language running on the language processor?
>
>I just  found myself wanting to reset a file pointer, and
>apparently OSARGS needs its block on the I/O processor zero
>page!

No, second processor zero page. When you subsequently
call OSARGS (on the second processor), the block is
transferred to the I/O processor for you, the call is
relayed, and any results are transferred back to the
second processor (and update the block if necessary).
This happens for practically all OS calls.

>How awkward is that? Okay, I can transfer my file pointer
>across with OSWORD 6.
>
>But... Can I happily use I/O 00.8F?

No.

>Are they all available to me, or has the Tube code got
>the rights to some of it it?

You should consider all language workspace to
be confiscated. I.e. &00-&8F and &400-&7FF.

But on the second processor the allocation of
language workspace is the same as on the I/O
processor (without the Tube active). E.g.
&70-&8F would be free if you run BASIC.

>Likewise for &400-&7FF - how much, if any, of that is available to me?

See above. None on I/O processor. Language
dependent on second processor.

>I understand that all of the I/O processor's OSHWM-HIMEM is available. 
>But is there any straightforward way of reading those settings from the 
>language processor? Presumably if I have some service code, if it asks 
>for OSHWM/HIMEM, it will get the I/O values, so I could use a user 
>OSWORD to get it to ask for me.

You will have to, yes. The second processor returns
its own OSHWM/HIMEM values via OSBYTE.

>And on a similar note - what does service code do if it needs some zero 
>page? There isn't anything obviously allocated for general non-language 
>use, just the few areas specifically allocated.

See above. On the I/O processor with the Tube active,
it's basically guesswork. You're not expected to run
any code there. That's the second processor's job.


John Kortink

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