heart_monitor.8o

# CHIP-8 Heart Monitor Simulation
# Copyright 2015 Matthew Mikolay
# See github.com/mattmikolay/chip-8 or mattmik.com for more info.

:alias y v0                     # y coordinate of wave sprite
:alias x1 v1                    # x coordinate of wave's right edge
:alias x2 v2                    # x coordinate of wave's left edge
:alias px v3                    # Temporary x coordinate used by subroutine
:alias mod_val v4               # Stores the value 32, used in calculations
:alias sound_reg v5             # Register used to play beeping noise

:const BEEP_LENGTH 15           # Duration of beeping noise
:const LINE_LENGTH 10           # Length of flat line before pulse occurs
:const WAVE_Y 9                 # y coordinate of wave sprite

: main

    clear

    # Set initial values
    x1 := 0
    x2 := 0
    y := WAVE_Y
    mod_val := 0b00011111
    sound_reg := BEEP_LENGTH

    # Draw starting line
    i := step1
    loop
        sprite x1 y 13
        x1 += 1
        if x1 != LINE_LENGTH then
    again

    loop

        # Draw (x1,y)
        px := x1
        read_i
        sprite x1 y 13

        # When the previous call to read_i terminates, px will store x1 % 32,
        # which we can use to determine if we should play a beep sound
        if px == 12 then
            buzzer := sound_reg

        # Draw (x2,y)
        px := x2
        read_i
        sprite x2 y 13

        # Increment x1 and x2
        x1 += 1
        x2 += 1

        # Wrap x1 and x2 to the 64 pixel wide screen
        if x1 == 64 then
            x1 := 0
        if x2 == 64 then
            x2 := 0

    again

# Reads memory address of corresponding sprite into i register based upon the
# current x coordinate stored in register px
: read_i

    # Get relative step, mod 32
    px &= mod_val

    # Load sprite based upon this relative step
    i := step1
    if px == 10 then
        i := step2
    if px == 13 then
        i := step3
    if px == 14 then
        i := step4
    if px == 15 then
        i := step5
    if px == 16 then
        i := step6
    if px == 17 then
        i := step7
    if px == 20 then
        i := step2

    return

: step1
    0b00000000

: step2
    0b00000000
    0b00000000
    0b00000000
    0b00000000
    0b00000000
    0b00000000
    0b10000000
    0b00000000 #

: step3
    0b00000000
    0b00000000
    0b00000000
    0b00000000
    0b00000000
    0b10000000
    0b10000000
    0b00000000 #
    0b00000000
    0b00000000

: step4
    0b00000000
    0b00000000
    0b00000000
    0b10000000
    0b10000000
    0b00000000
    0b00000000
    0b00000000 #
    0b00000000
    0b00000000
    0b00000000
    0b00000000
    0b00000000

: step5
    0b10000000
    0b10000000
    0b10000000
    0b00000000
    0b00000000
    0b00000000
    0b00000000
    0b00000000 #
    0b00000000
    0b00000000

: step6
    0b00000000
    0b00000000
    0b00000000
    0b10000000
    0b10000000
    0b10000000
    0b10000000
    0b10000000 #

: step7
    0b00000000
    0b00000000
    0b00000000
    0b00000000
    0b00000000
    0b00000000
    0b00000000
    0b00000000 #
    0b10000000
    0b10000000
    0b10000000
    0b10000000
    0b10000000