#### fun for MARS/MIPS/MIDI : "un canon pour MIDI"
#### CSC4536 Pascal Hennequin
#### original code by Luke Tannenbaum: github.com/TheCodeOfLife/

.data # Pachelbel Canon
syscalls: .byte 31, 31, 33, 33, 33, 33, 31, 31, 33, 33, 33, 33,
	  	31, 31, 33, 33, 33, 33, 31, 31, 33, 33, 33, 33,
	  	31, 31, 33, 33, 33, 33, 31, 31, 33, 33, 33, 33,
		31, 31, 33, 33, 33, 33, 31, 31, 33, 33, 33, 33
notes: 	  .byte 74, 70, 58, 58, 62, 65, 72, 65, 53, 53, 57, 60,
	  	70, 67, 55, 55, 58, 62, 69, 62, 50, 50, 53, 57,
	  	67, 63, 51, 51, 55, 58, 65, 58, 46, 46, 50, 53,
		67, 63, 51, 51, 55, 58, 69, 65, 53, 53, 57, 60
durees:	  .byte  4,  4,  1,  1,  1,  1,  4,  4,  1,  1,  1,  1,
	  	 4,  4,  1,  1,  1,  1,  4,  4,  1,  1,  1,  1,
	  	 4,  4,  1,  1,  1,  1,  4,  4,  1,  1,  1,  1,
		 4,  4,  1,  1,  1,  1,  4,  4,  1,  1,  1,  1
instrums: .byte 19, 19, 30, 48, 48, 48, 19, 19, 30, 48, 48, 48,
	  	19, 19, 30, 48, 48, 48, 19, 19, 30, 48, 48, 48,
	  	19, 19, 30, 48, 48, 48, 19, 19, 30, 48, 48, 48,
		19, 19, 30, 48, 48, 48, 19, 19, 30, 48, 48, 48
.data # params
length:   .word  48   # array length (unused, auto-computed) 
xduree:   .word 250   # facteur durée 100-1000
volume:   .byte  60   # 0-127
transpo:  .byte -12   # transposition note (octave == +-12) 

.text
# $s0 array index
# $s1 array length
# $s4 duration scale
# $s5 note tansposition
main:
    lw $s4, xduree
    lb $s5, transpo
# array length ->$s1
    la $t6, syscalls
    la $t7, notes
    sub $s1, $t7, $t6
# play ...
    jal play
    addi $s5, $s5, -12  # octave -1
    jal play
    addi $s5, $s5, +24  # octave +2
    jal play
# play forever
    j main
#exit
    li $v0, 10 
    syscall

play: 
    li $s0, 0       #loop index
loop:
# note
    lb $v0, syscalls($s0)
    lb $a0, notes($s0)
    lb $a1, durees($s0)
    lb $a2, instrums($s0)
    lb $a3, volume
# modifs
    add $a0, $a0, $s5
    mult $a1, $s4 
    mflo $a1
# MIDI play 
    syscall  
# loop/returns
    addi $s0, $s0, 1
    bne $s0, $s1, loop
    jr $ra