Re: [cc65] Uniform mass storage device discovery and file locations

From: "Oliver Schmidt"; on Friday, August 24, 2012; at 1:15 PM -0400
>
>> Those issues are why CBM-Command does it at a higher level (OPEN, CLOSE,
>> READST).  Look at "driveRoutines.s":
>> http://cbmcommand.codeplex.com/SourceControl/changeset/view/76273#841469
>
> Isn't that the approach that was classified as undesirable, before in
> this thread, because it causes "drive noise" if there's no disk in the
> drive?

These are different DOS commands:
"I" initiates a disk -- it can "bang" the head.
"UI" resets the DOS -- it doesn't try to touch any disks.
("U9" is an old alias of "UI".)

Only programs on the Pet platform send the "UI" command.

On Commodore's computers with the IEEE bus, the ROM's CLOSE function 
doesn't give us an indication of errors .  Therefore, we must make OPEN 
attempt to talk to devices.  We do that by giving OPEN a "file-name" string 
(the string is sent to the unit's command/status channel; therefore, it's 
obeyed, instead of openning a file).  I chose "UI" simply because 
CBM-Command uses that command later, anyway.  (But now, I think that I 
might change it to the more benign command "U0".  It resets some pointers 
that almost never are changed -- so, it's a no-op.)

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