Alien 8: Routine at B690

B690: A warble for the remote-controlled robots

Used by the routines at REMOTE_ROBOT and SLOW_CHASER.

A few single waves, their pitch scrambled from the turn counter and the step count with an XOR. How many is read from a table at HL, indexed by the turn counter's low two bits: REMOTE_ROBOT passes WARBLE_COUNTS, SLOW_CHASER the fifth byte of it, so the two run through different parts of the same rise and fall.

Input
HL	the table of wave counts (WARBLE_COUNTS, or four bytes into it)

WARBLE_SOUND

B690

LD A,(TURNS)

C = the table's entry for the turn counter's low two bits

B693

AND $03

B695

CALL ADD_HL_A

B698

LD C,(HL)

WARBLE_SOUND_0

B699

LD A,(TURNS)

one wave at half-wave count 64 + ((turns XOR C) AND 31)

B69C

XOR C

B69D

AND $1F

B69F

OR $40

B6A1

LD B,A

B6A2

CALL CLICK

B6A5

DEC C

until C runs out

B6A6

JR NZ,WARBLE_SOUND_0

B6A8

RET