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Elite on the BBC Micro

Sound: NOISE (Master version)

Name: NOISE [View in context] Type: Subroutine [Compare versions] Category: Sound Summary: Make the sound whose number is in Y by populating the sound buffer
The following sounds can be made by this routine. Two-part noises are made by consecutive calls to this routine with different values of Y. The routine doesn't make any sounds itself; instead, it populates the sound buffer at SBUF with the relevant sound data, and the interrupt handler at IRQ1 calls the NOISE2 routine to process the data in the sound buffer and send it to the 76489 sound chip. This routine can make the following sounds depending on the value of Y: 0 Long, low beep 1 Short, high beep 3, 5 Lasers fired by us 4 We died / Collision / Our depleted shields being hit by lasers 6 We made a hit or kill / Energy bomb / Other ship exploding 7 E.C.M. on 8 Missile launched / Ship launched from station 9, 5 We're being hit by lasers 10, 11 Hyperspace drive engaged Arguments: Y The number of the sound to be made from the above table
.NOISE \ This routine appears to set up the contents of the \ SBUF sound buffer, so the NOISE2 routine can then send \ the results to the 76489 sound chip. How this all \ works is a bit of a mystery, so this part needs more \ investigation LDA DNOIZ \ If DNOIZ is non-zero, then sound is disabled, so BNE SRTS \ return from the subroutine (as SRTS contains an RTS) LDA SFX2,Y \ Fetch SFX2+Y and shift bit 0 into the C flag LSR A CLV \ Clear the V flag LDX #0 \ If bit 0 of SFX2+Y is set, set X = 0 and jump to NS1 BCS NS1 INX \ Increment X to 1 LDA SBUF+13 \ If SBUF+13 < SBUF+14, set X = 1 and jump to NS1 CMP SBUF+14 BCC NS1 INX \ SBUF+13 >= SBUF+14, so increment X to 2 .NS1 \ By the time we get here, X is set as follows: \ \ * X = 0 if bit 0 of SFX2+Y is set \ * X = 1 if SBUF+13 < SBUF+14 \ * X = 2 if SBUF+13 >= SBUF+14 LDA SFX1,Y \ Set A = SFX1+Y CMP SBUF+12,X \ If SFX1+Y < SBUF+12+X, return from the subroutine BCC SRTS SEI \ Disable interrupts while we update the sound buffer \ If we get here then SFX1+Y >= SBUF+12+X STA SBUF+12,X \ SBUF+12+X = A = SFX1+Y LSR A \ Store bits 1-3 of SFX1+Y in bits 0-2 of SBUF+6+X AND #%00000111 STA SBUF+6,X LDA SFX4,Y \ Store SFX4+Y in SBUF+9+X STA SBUF+9,X LDA SFX2,Y \ Store SFX2+Y in SBUF+3+X STA SBUF+3,X AND #%00001111 \ Store bits 1-3 of SFX2+Y in bits 0-2 of SBUF+15+X LSR A STA SBUF+15,X LDA SFX3,Y \ Set A = SFX3+Y BVC P%+3 \ If the V flag is set, double the value in A ASL A STA SBUF+18,X \ Store A in SBUF+18+X LDA #%10000000 \ Set bit 7 of SBUF+X STA SBUF,X CLI \ Enable interrupts again SEC \ Set the C flag RTS \ Return from the subroutine