Hi,
About stopping the diskdrive after disk actions:
This particular address mentioned earlier contains a drive-off
counter. It is set to, I think, 254, after every disk action, and
decreased 1 on every call to the diskROM's interrupt handler (so
every timing-interrupt). If it reaches zero (so after some 5
seconds), the drive motor is stopped. If THIS drive is accessed again
in the meanwhile, the interval starts again. The value 255 has a
special meaning: 'keep running'. If you do something with the drive,
and POKE 255 in this memory location quickly (before the counter
reaches zero), this diskdrive motor simply keeps running.
The address is simply the same on many MSX machines, because they use
similar working diskROM(s), but it is NOT a fixed address in any way,
not documented, not guaranteed or such, in one word: don't rely on
something like this, if you do, someone will have troubles because of
it, some other time.
I figured out this approach to stopping disk drive motor(s, note
there might still be another drive running, if you start this game
quickly enough from a different one):
LD IX,#4029
LD IY,(#F347)
CALL #001C
This is a call to a diskROM entry, which (should) contain a routine
that 'scans' all diskROMs, and calls another entry in each, which
should be present in each diskROM, to stop the drive. The address
F348h contains the slot-address of the 'main' diskROM (the first one,
that handles the initialising stuff and so on), the address 4029h is
one of a small number of entries present in any diskROM, and are
described in the MSX Technical Databook (I'm not sure if they're also
in the MSX2 Tech Handbook). You can call the method above pretty
solid, and it should work whenever there IS a diskdrive (contents of
FFA7h<>C9h).
But: on using this myself, I found these drawbacks:
-It stops DRIVE-motors, doesn't do anything with other
interrupt-related processes that might be running.
-On my Novaxis SCSI, it stopped the HDD motor as well (great, mine
made a lot of noise). But those stupids from Gouda did implement this
diskROM-entry, but forgot to turn on the drive again when accessed,
in case it was shut down this way (! stupid, stupid...)
So, shutdown the drives this way, and you'd have to reset the machine
again, just to get the HDD spinning again (I switched it on and off
instead).
-This diskROM-entry might not be (properly, or not at all)
implemented with a particular disk system
I would say calling the hook at FD9Fh 256 times (do yourself a favor,
no less than 256..), is by far the best, AND most
compatible/problem-free way of shutting down disk-drives and such.
I'd say this IM2 approach is not a bad idea (and yes, there need to
be 257 of the same values on the address I*256), it prevents you from
HAVING to switch RAM in page 0, and you can select a different
starting address for your interrupt routine, which is called
immediately on each interrupt, rather than having to wait for a few
instructions at #0038 to get executed first, before a hook-address is
called.
If you'd switch RAM in page 0, you'd also have to setup at least the
slotswitching-routines, which are the same under DOS, BASIC, and even
present in MSX-2 subROM. I'd say, a lot of work.
Best way would be to use this IM2-approach during run-time, using
all 'common' hardware (VDP, keyboard etc.) by direct I/O (remember
any BIOS call might re-enable interrupts, and mess up things when
you'd expect these to be off at that time), and temporarily switching
back to IM1, and restoring memory settings etc. when making any BIOS
or disk CALLs.
Your program might have a setup like this:
On startup:
-Store any memory settings, in case you need to change, and restore
these later
(other initialisation)
-Set up your interrupt handler
-Set up this 257 byte table (interrupt handler at address
257*fillbyte), starting at a 256-byte boundary (low byte 0)
-Set Z80 I-register to the high byte of the address of this table
-switch to IM 2
-enter a main loop of your program
On a disk-access/BIOS-call:
-restore memory settings, if needed, possibly update some system
memory locations containing VDP-register contents and so forth
-switch back to IM 1
-make your BIOS/disk CALL
-(.. make some more disk CALLs)
-call FD9Fh 256 times
-switch to IM 2 again
On exit:
-Do the same restoring as before
-Switch back to IM 1
If that still doesn't do it:
-Use a faster METHOD of obtaining your goal
-Write even faster code
-make a turbo-circuit (6/7 MHz. or my own) a system requirement
-or make it a TurboR program
Greetings,
Alwin Henseler ([EMAIL PROTECTED])
http://huizen.dds.nl/~alwinh/msx (MSX Tech Doc page)
http://www.twente.nl/~cce/index.htm (Computerclub Enschede)
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