b $C2E8 data used by sound routine
B $C2E8 outer loop counter
B $C2E9 inner loop counter
B $C2EA four "delay" counters used by $C33A
B $C2EE four bytes which are added to the previous four bytes at the end of the sound routine


c $C2F9 Sound routine - data block format: outer loop counter, inner loop counter, first set of four bytes controlling delay loop before playing a sound byte, second set of four bytes controlling delay loop before playing a sound byte
; @label:$C2F9=$C2F9
C $C2F9 set destination address (data block at $C2E8)
C $C2FC ten bytes to be copied
C $C2FF copy ten bytes from where HL is pointing (by caller) to the data block at $C2E8

C $C301 disable interrupts
C $C302 point HL at $C2E8 (a data block of ten bytes for the current sound)
C $C305 load first byte into B - i.e. initialise loop counter
C $C306 preserve BC - outer loop counter
C $C307   point HL at $C2E9 - 2nd byte of data block
C $C30A   load 2nd byte of data block into B - inner loop counter
C $C30B   preserve BC - inner loop counter
C $C30C   set B to four - loop counter
C $C30E     point HL at third byte of data block
C $C311     preserve BC and HL
C $C313       load next byte from data block into B - counter used by $C33A below
C $C314       call $C33A which just counts down from B to zero before returning (?!)
C $C317       load A with value of unknown57 (initially $30) - sound byte to play?
C $C31A       XOR with $30 (110000 in binary) - toggle sound byte; black border
C $C31C       store result in unknown57 (current sound byte to play?)
C $C31F       write value in A to the loudspeaker (either $0 or $30)
C $C321       restore HL which is pointing into the data block
C $C322       increment HL to point to the next byte in the data block
C $C323       restore loop counter
C $C324       loop back to $C311 three times
C $C326       restore BC
C $C327     loop back to $C30B "second byte in data block" times
C $C329     load B with $04
C $C32B     exchange contents of DE and HL - DE points at wherever HL is up to
C $C32C     point HL at 3rd byte in data block at $C2E8
C $C32F     let (HL) = (HL) + (DE) - so the last 4 bytes in the data block are added to the preceding four
C $C332 increment DE and HL
C $C334 loop back to $C32F three times
C $C336 restore BC
C $C337 loop back to $C306 "first byte in data block" times
C $C339 return to caller