Routines
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45786: Play Note
Used by the routines at PlayMusic_WaitKey and PlayMusic.
Plays a note of a tune, or a rest if the note number is zero. Bits 0 to 5 select the entry in MusicNotes that holds the two delays of a cycle and the number of cycles. Bits 6 and 7 are the length less one, which multiplies the number of cycles, so the note is one to four times as long.
Input
A The note
DE Address of the note
Output
DE Address of the next note
Look up the delays and the number of cycles.
PlayNote 45786 AND %00111111 Isolate the number of the note.
45788 JR Z,PlayNote_Rest Jump to PlayNote_Rest if the note is a rest.
45790 LD L,A Set HL to the note number.
45791 LD H,0
45793 ADD HL,HL Double the number.
45794 CALL AddAToHL Call AddAToHL.
Point HL at the entry of the note in the table, MusicNotes.
45797 LD BC,45874 Point BC at MusicNotes.
45800 ADD HL,BC Find the entry for the note.
Fetch the first byte of the delay between the clicks of the speaker.
45801 LD B,(HL) Fetch the first delay.
45802 INC HL Move on.
Fetch the second byte of the delay.
45803 LD C,(HL) Fetch the second delay.
45804 INC HL Move on.
Fetch the basic length of the note.
45805 LD L,(HL) Fetch the number of cycles.
45806 LD H,0 Set H to 0.
Bits 6 and 7 are the length, less one.
45808 LD A,(DE) Fetch the note again.
45809 RLCA Move bits 6 and 7 to bits 0 and 1.
45810 RLCA
Isolate the length of the note.
45811 AND %00000011 Isolate the length of the note.
Make it 1 to 4.
45813 INC A Add one.
45814 PUSH DE Stash the note address on the stack.
45815 LD E,L Copy the number of cycles to DE.
45816 LD D,H
Multiply the number of cycles by the length.
PlayNote_Multiply 45817 DEC A Count down the length.
45818 JR Z,PlayNote_MultiplyDone Jump to PlayNote_MultiplyDone if the length has been used up.
45820 ADD HL,DE Add the number of cycles again.
45821 JR PlayNote_Multiply Jump to PlayNote_Multiply.
PlayNote_MultiplyDone 45823 POP DE Restore the note address from the stack.
Each pass makes one cycle of the note.
PlayNote_Cycle 45824 PUSH BC Stash the delays on the stack.
45825 XOR A Set A to 0.
45826 OUT (254),A Turn the speaker off.
PlayNote_OffDelay 45828 DJNZ PlayNote_OffDelay Wait with the speaker off, using the first byte of the delay for the first pass and 256 for each pass after it.
45830 DEC C Count down the second delay.
45831 JR NZ,PlayNote_OffDelay Jump to PlayNote_OffDelay until it has finished.
45833 POP BC Restore the delays from the stack.
45834 PUSH BC Stash the delays on the stack.
45835 LD A,16 Set bit 4.
45837 OUT (254),A Turn the speaker on.
PlayNote_OnDelay 45839 DJNZ PlayNote_OnDelay Wait with the speaker on for the same length of time.
45841 DEC C Count down the second delay.
45842 JR NZ,PlayNote_OnDelay Jump to PlayNote_OnDelay until it has finished.
45844 POP BC Restore the delays from the stack.
45845 DEC HL Decrease the number of cycles left to play.
45846 LD A,H Jump to PlayNote_Cycle until there are none left.
45847 OR L
45848 JR NZ,PlayNote_Cycle
45850 INC DE Point at the next note.
45851 RET Return.
A rest is a silent pause of one to four units.
PlayNote_Rest 45852 LD A,(DE) Fetch the length of the rest.
45853 INC DE Point at the next note.
45854 RLCA Rotate bits 6-7 of the note into the low bits.
45855 RLCA
45856 AND %00000011 Keep bits 0 and 1.
45858 INC A Add one.
45859 LD L,A Keep it in L.
45860 LD BC,17163 Set BC to 17163.
PlayNote_RestUnit 45863 PUSH BC Stash the pause length on the stack.
PlayNote_RestDelay 45864 DEC BC Count down the pause.
45865 LD A,B Jump to PlayNote_RestDelay until the length of the wait is zero.
45866 OR C
45867 JR NZ,PlayNote_RestDelay
45869 POP BC Restore the pause length from the stack.
45870 DEC L Count down the units of the rest.
45871 JR NZ,PlayNote_RestUnit Jump to PlayNote_RestUnit until it is zero.
45873 RET Return.
View the equivalent code in;
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