SFG05 Access

Well, it's still a mystery as indicated as remarks in the blueMSX source :

After hours of disassembling the MIBIOS I found something interesting:
Yamaha uses a byte somewhere in the ROM variables (F9A5h - this is somewhere in the middle of the music queue of Voice A) to save the state of the last write command to the 3FF6h.
(These area is previously saved from overwriting and cannot destroyed from "normal" BIOS - the "PLAY" ROM variable is overwritten with a RET command))

and sometimes the content of these byte is taken and processed and rewritten to 3FF6h like this:

LD HL,0F9A5H
LD A,(HL)
OR 02H
LD (HL),A
 LD (3FF6H),A

	LD A,(0F9A5H)
	RES 3,A			; Bit 3 IRQon is set to zero
	LD (0F9A5H),A
	LD A,(0F9A5H)                           ; mystery
	LD (3FF6H),A

LD A,(0F9A5H)
PUSH AF
AND 67H		; mask Bit 7,4,3
LD (0F9A5H),A
LD (3FF6H),A
EI
NOP
DI

unfortunally these variables in the music queue aren´t nowhere described and I´m going deeper and deeper and what I previously said: the mystery grows up! Yamaha uses a lot of variables in these space. They all setup in an endless subroutine.

The next I want to do is to follow the R- and M-calls in the MBIOS to get some information how to handle the 3FF6 Register.

I have disassembled the whole code from 0000h to 3FFFh and working on a clear listing in my assembler. If I´m ready with that, in one or two years, I´m back with my work

Is someone out there who have deeper informations?

EDIT:

this is interesting, it waits for something:

	LD A,(0F9A5H)
	PUSH AF
	AND 67H		; mask Bit 7,4,3
	LD (0F9A5H),A
	LD (3FF6H),A
L0655:  EI
	NOP		; gives interrupt a chance
	DI
	LD A,(0F9A2H)
	LD C,A
	LD A,(0F9A3H)
	CP C
	JR NZ,L0655
	POP AF
	AND 0FDH
	LD (0F9A5H),A
L0654:  LD B,5AH
L0656:  DJNZ L0656
	LD A,05H
	LD (3FF6H),A
	IM 1
	POP BC
	POP AF
	RET

After years, I´ll come back with this work.
Have much more expieriences with VDP and someone more....
I have simply modified the Code from Yamaha Goteborg MAP.GEN and got a simple MIDI THRU machine, without any screen Action.
It works fine on my real CX5M.
This is the main Loop:

THRLOOP:   CALL INMD
           LD   HL,DATABUF
           LD   (HL),D
           LD   A,D
           CP   #E0  ;PITCH WHEEL CH 1?
           JR   Z,THREND  ;RETURN TO BASIC
           CALL OPMD
           JR   THRLOOP
THREND:    CALL BACK
           RET

I can go out of this Loop with pitch on channel one.
All is fine.
But my question is, how can I Interrupt this Loop with keycommands?
I´m always inside the SFG05 wit DI.
Is this the way? (excerpt from above)

L0655:  EI
	NOP		; gives interrupt a chance
	DI

I´ve tried it in my other code where I have a Loop they wait for MIDI Input:
it´s almost the same from Yamaha Goteborg Code

INMD:  XOR D
       EI    ; Interrupt to get KEY is pressed? is that enough? Do I have to put a NOP after this?
       CALL CHECKBUFF  ; I´ve copied the BIOS code for this into RAM because of other SLOT
       JP NZ, KEYPR    ; if key is pressed then go to OUT Routine
       DI
       LD A,(MIDSTATR)       ;get status from Statusregister
       LD (MIDSTAT),A
      BIT 5,A                    
      JR  NZ,FE  ;if bit 5 of status is set then Framing Error
      BIT 1,A                    ;
      JR Z,INMD ;if bit 1 of status is zero, not ready yet,again

EI ; Interrupt to get KEY is pressed? is that enough? Do I have to put a NOP after this?

CHECKBUFF: LD HL,(0F3FAh)  ; GETPTN      Keyboardbuffer
           LD A,(0F3F8h)   ; PUTPNT
           SUB L   ; check if same      SET Z if empty
           RET

EDIT:
that doesn´t work, I got no Keyaction, the program hangs...

INMD:  XOR D
       EI
       NOP
       DI
       CALL CHECKBUFF
       JP NZ, KEYPR    ; if key is pressed then go to OUT Routine

Doesn’t MBIOS do the IM2 mode interrupt handling for you? I remember reading that in the application manual…

Sorry... I newer dived in to MIDI stuff as I didn't have MIDI keyboard or cables.

Really? This is first time I remember hearing that IM2 mode is used on MSX. In IM2 mode the interrupt jump address is formed by reading 16bit value from address pointed by register I (hi byte) and value in databus (lo byte).

If you can't decipher the correct databus values from the MBIOS, then maybe you can adapt this source for your needs:

; DATABUS Ver 2.1 for MSX (Made By: NYYRIKKI)
;
; This program reads a value from databus when 
; Z80 leaves databus control to peripherals.
;
; Usage from MSX-BASIC:
;
;	BLOAD "DATABUS.BIN",R:PRINT USR(0)
;
;-----------------------------------------------------------------------------------------

USR:	EQU #F7F8
USR0:	EQU #F39A

	DEFB #FE
	DEFW BEGIN
	DEFW END
	DEFW START

	ORG #B000

BEGIN:
START:
	LD HL,CODE
	LD (USR0),HL
	RET
CODE:
	DI
	LD HL,#BF00
	LD BC,0

NEXT:
	LD A,C
	ADD A,B
	CP #10
	JP NC,NOMORE

	LD (HL),A
	INC HL

	CP #F
	JP Z,SKIP
	LD (HL),B
	INC HL

SKIP:
	INC C
	LD A,C
	CP #10
	JP NZ,NEXT

NOMORE:
	LD C,0
	INC B
	LD A,B
	CP #10
	JP NZ,NEXT

	LD (HL),#C0

	LD HL,#BF00
	LD DE,#BE00
	LD BC,0

FIXL:
	LD A,(HL)
	LD C,A
	OR #C0
	LD (HL),A
	INC HL
	LD A,(HL)
	RLCA
	RLCA
	RLCA
	RLCA
	OR C
	LD E,A
	EX DE,HL
	LD A,E
	DEC A
	LD (HL),A
	EX DE,HL
	DJNZ FIXL

	LD HL,#C0C0
	LD DE,#C0C1
	LD B,#10

MAKEPROG:
	PUSH BC
	LD BC,#F
	PUSH HL
	PUSH DE
	LD (HL),4	;INC B
	LDIR
	LD (HL),#CD	;CALL
	INC HL
	LD DE,CALCUT
	LD (HL),E
	INC HL
	LD (HL),D
	POP DE
	POP HL
	POP BC
	INC H
	INC D
	DJNZ MAKEPROG

	LD A,#BF
	LD I,A

	IM 2
	EI
	NOP
	HALT	; Any interrupt will be accepted.

	LD L,A
	LD H,#BE
	LD A,(HL)
	LD (USR),A
	XOR A
	LD (USR+1),A
	RET


CALCUT:
	POP AF
	AND #F
	RLCA
	RLCA
	RLCA
	RLCA
	OR B
	XOR #F
	IM 1
	EI
	RETI

END: