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⌂ ∞ ▽ Elite on the 6502

Sound: LASNOISE

[Apple II version]

       Name: LASNOISE                                                [Show more]
       Type: Subroutine
   Category: Sound
    Summary: Make the sound of our laser firing or the sound of us being hit by
             lasers

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * Main flight loop (Part 3 of 16) calls LASNOISE
             * TACTICS (Part 6 of 7) calls LASNOISE




.LASNOISE

 LDY #11                ; Set the length of the loop below to 11 clicks, so we
                        ; make a total of 12 clicks in the following

 LDX #150               ; Set the period of the sound at 150, which increases
                        ; as the sound progresses

.SOBLOP

 BIT DNOIZ              ; If bit 7 of DNOIZ is non-zero, then sound is disabled,
 BMI SOUR               ; so return from the subroutine (as SOUR contains an
                        ; RTS)

 STX T3                 ; Store the period in T3

.BEEPL3

 LDA $C030              ; Toggle the state of the speaker (i.e. move it in or
                        ; out) by reading the SPEAKER soft switch

 INC T3                 ; Increment the period in T3 twice, so the tone of the
 INC T3                 ; sound falls rapidly

 LDX T3                 ; Loop around for T3 iterations, so as the sound
 DEX                    ; continues and T3 increases, the wait gets longer and
 BNE P%-1               ; the frequency of the laser tone lowers into a
                        ; dissipated explosion noise

 DEY                    ; Decrement the sound length in Y

 BNE BEEPL3             ; Loop back to make another click and wait for a rapidly
                        ; increasing amount of time between clicks, until we
                        ; have made a sound consisting of Y clicks

 LDA $C030              ; Toggle the state of the speaker (i.e. move it in or
                        ; out) by reading the SPEAKER soft switch

 RTS                    ; Return from the subroutine