[Coco] Max number of floppy drives with DOS

Francis Swygert farna at att.net
Wed May 19 07:33:45 EDT 2021

Date: Tue, 18 May 2021 09:58:08 +0000
From: rietveld rietveld <rietveldh at hotmail.com>

I actually played with this MPI solution last night using POKE 65407,51 and POKE 65407,34 to software select the controllers.  I have a double sided 5 1/4 and 3 1/2 in slot 4 and a pair of double sided 5 1/4 drives in slot 3.
I am just playing around with a RAMDISK to act as the go between. I can copy from physical disk to RAMDISK then POKE a slot select and copy from RAMDISK to the other set of drives.
The only problem is that you're actually switching ROMs as well. With a CoCo2 this would be problematic, but on a CoCo3 that loads the ROMs into RAM at startup, I suppose it keeps the ROM from the first controller active... or does it re-load the ROM from the active controller when the slot is changed? As long as both ROMs are identical it probably doesn't matter, but this is interesting. So what happens with the ROM when the slots are changed? Nothing, or does it re-load? Won't matter with OS-9, of course, you just need to keep up with which controller is being used. I suppose a driver could be written that selected the correct slot when a certain drive number was chosen. The default controller being the main drives, the second controller having modified drivers so that when that drive number was chosen it would switch slots. Hmmm.... the default drivers would need to be changed to select the correct slot also, or the secondary drivers would need some way to switch back the the primary when an operation completed. 

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