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Music Processor

The music processor can be thought of as an independent CPU handling all output to the music/noise ports. The MUZCPU has 4 registers:

MPC Like all program counters, points to the next data byte to fetch.
MSP Like a stack pointer, points to return addresses on the stack.
DURATION Loaded at the start of a note, then decremented every 60th of a second.
VOICES A status register that tells which voices (tones) to load with what data.

The voices status register is shown below. Execution proceeds right-to-left. Make sure that you always have at least one PC incrementing bit or load on.

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Music System Routines

Name Description
BMUSIC Begin playing music
EMUSIC Stop music

Music System Routine Descriptions

BMUSIC

BEGIN PLAYING MUSIC

Calling Sequence: 
SYSTEM    BMUSIC

or 

SYSSUK    BMUSIC
DW        (music stack)
DB        (voices byte)
DW        (score)
Arguments: A = voices to start with
HL = music program counter (score)
IX = music stack pointer
Notes: None
Description: Quiets any previous music, then interprets specified “score.”
Restrictions: None

EMUSIC

STOP MUSIC

Calling Sequence: 
SYSTEM    EMUSIC

or 

SYSSUK    EMUSIC
Arguments: None
Notes: None
Description: Outputs 0 to volume ports and halt music processor.
Restrictions: None

MUZCPU Instruction Set

# OF BYTES MNEMONIC COMMENT
2 VOICES,(data) ;VOICES=(data)
2 MASTER,(data) ;TONE0=(data)
3 CALL,(address) ;(SP)=(PC+3) PC=address
1 RET ;PC=(SP++)
3 JP,(address) ;PC=address
2 NOTE1 ;Duration, note or data (D1)
3 NOTE2 ;Duration, D1,D2
4 NOTE3 ;Duration, D1,D2,D3
5 NOTE4 ;Duration, D1,D2,D3,D4
6 NOTE5 ;Duration, D1,D2,D3,D4,D5
2 REST ;Duration in 60ths of a second
Pauses silently (except during LEGATO)
1 QUIET ;Stops music and sets volume=0
2 OUTPUT ;Port #, Data
9 OUTPUT ;SNDBX,DATA10,D11,D12,D13,D14,D15,D16,D17
3 VOLUME ;(VOLAB),(VOLMC) sets volume for notes
1 PUSHN ;Push # between 1-16 onto the stack
1 CREL ;Call relative to next instruction
3 DSJNZ ;Decrement stack top and jump if not 0, else pop stack
1 LEGSTA ;Flips between STACATO and LEGATO modes
STACATO is clipped 1/60th before the end of each note
LEGATO allows one note to run into the next

Note: All durations are limited to a maximum of 127

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Music Score Example

          VOICES     11010100B     ;ABC=Data 1
          MASTER     0A1H          ;ABC=1/2
          VOLUME     88H,08H
          NOTE1      12,A1
          NOTE1      12,C2
          NOTE1      24,E2
          NOTE1      12,C2
          NOTE1      12,E2
          REST       6
          VOICES     11110110B     ;Suck in Vibrato, AB and C bytes
          NOTE3      12,14,A2,E2
          QUIET

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