[Coco] MPI and NitrOS-9

[Gene Heskett]

On Sunday 08 December 2013 00:05:45 Bill Gordon did opine:

> I've been able to "jump" between drives using the pokes to access the
> slots on the MPI in Disk Extended Color Basic, but I'm wondering is
> there a way that slots other than the drive controller slot (Slot 4)
> can be accessed with NitrOS-9?
> 
You may find the assembly source for the clock modules interesting reading.  
Way back when I was trying to make serial comm, and the B&B XT-RTC clock 
live together on level 1, I came across something that explained that in 
the IRQ search for where it came from routine.

Generally each module of code that needs to access a slot other than 3, 
which you know as 4, will read and save that current value of the slot at 
$FF7F, set it to what that driver needs, and when its done, reset it to 
what was there before, or to $33, but with a jumpered MPI such as I have 
mentioned many times, the nibble that control IRQ steering can be anything 
without blocking an IRQ and making the modem miss a character.  But you'll 
have to look that up as I have long since forgotten which of the two 3's is 
the important one.  With the MPI jumpered, there is at least 50 bytes of 
code in the clock modules that could be elided.
> 
> Thanks
> 
> 
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Cheers, Gene
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