>> The point is that (a) the MIDI OUT interrupt is quite difficult to
catch
>> if there are line and frame interrupts going on as well because you
coul
>> easily miss one while the interrupts are disabled; and (b) you don't
need
>> that flag because in(248) already contains one (bit 1).
>>
>> imc
>>
>
>Thanks Ian, you beat be to it there.
>
>My interrupt handler works like this at the minute...
Hmmm... personally, I'd do it like this:
int.handler: PUSH AF
IN A,(INTSTAT)
BIT 2,A ; midi out bit? can't remember
CALL NZ,midiout
RRA
CALL NC,lineint
BIT 2,A ; now check for frame interrupt...
EI
JP NZ,exitint
; we've done all the short interrupts, so re-enable
frame: ; this is more longwinded and complicated, so...
frameflag: LD A,0x00 ; check if we're already in frame handler
OR A ;if so, early abort
JP NZ,exitallint
CPL
LD (frameflag:d),A
; push everything we need onto the stack, and do our
; frame interrupt stuff
;... and then clear frameint flag
DI ;just in case... we don't want to nest, so make sure
;that we have a clean stack - this way, interrupts
;won't come back until AFTER the RET at the end of
;the routine
XOR A
LD (frameflag:d),A
exitint: POP AF
EI ;inexpensive safety check
RET
midiout: PUSH AF
XOR A
LD (outmididata:d),A ;reset the "wait" flag.
exitmidi: POP AF
RET
line: ; only do simple stuff here...
PUSH AF
;blah
POP AF
RET
; Return NZ if not ready to output data version
outmididatanz: LD A,(outmididata:d)
OR A
RET NZ
JR outmidi
; Spinlock version of midi out routine
outmididata: LD A,0x00
OR A
JP NZ,outmididata ;data already queued, so spin round
outmidi: CPL
LD (outmididata:d),A
LD A,E
OUT (MIDIOUT),A
RET
I don't have my tech manual in the office, so I can't look up that flag;
however, this routine could be easily modified to use it.
You could, of course, also build your own FIFO for the MIDI OUT
interrupt to use. It's similar logic - you have to make sure that your
starting conditions are correct though.
Also, the frame interrupt trick is very handy - that way you can do all
your key checking every frame (which is necessary for good key response
- 25Hz gives dropped keys, at least for me), and mouse checks, etc etc
without dropping other interrupts. I used this in TERMITE, and it works
decidedly well - even at 57,600KHz.
Simon
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