Date   : Tue, 01 Dec 2009 02:34:20 +0000
From   : kevin@... (Kevin Bracey)
Subject: Tube - I/O processor memory questions

Jonathan Graham Harston wrote:
> Kevin Bracey wrote:
>   
>> Exactly what memory is available on the I/O processor for a language
>> running on the language processor?
>>     
>  
> None. A language is only allowed to use memory in the language
> processor. It is absolutely forbidden to use any other memory.
>   
Says who? All the docs I've seen state unambiguously that the I/O 
OSHWM-HIMEM area is normally available for the user or language. It was 
only the below-OSHWM areas where there seemed to be any doubt.

Who do you think has the rights to that area?

Clearly there are some heavy *-Commands that splat the area, as normal; 
and there's the printer buffer than came with the copro that use that 
area, but that's semi-apologetic about it and says it should only be 
used if you're not using the I/O RAM. The clear implication being that 
you may well be:

"This buffer uses RAM in the I/O processor between &4000 and &8000 and 
should not be used where your own application makes use of this area of 
I/O memory."

I've certainly not seen any suggestion that anyone else has gained more 
rights to it than the language/user.

>  
> If you are transient code running in the I/O processor, use the
> memory locations allocated and documented as available for such use
> - &A8 to &AF.
>   
Aha, so that's intended for general third party service code use? 
Where's that documented? The references I've seen just have it down as 
for "operating system scratch space" or the like.

Kevin