The BDRO9 subroutine - Elite on the 6502

       Name: BDRO9                                                   [Show more]
       Type: Subroutine
   Category: Sound
    Summary: Process music command <#9> to restart the current tune
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * BDJMPTBH calls BDRO9
             * BDJMPTBL calls BDRO9
             * BDRO11 calls BDRO9


.BDRO9

 LDA #0                 ; Clear the current music data byte, which discards the
 STA BDBUFF             ; next nibble if there is one (so this flushes any data
                        ; from the current pipeline)

 LDA BDdataptr3         ; Set BDdataptr1(1 0) = BDdataptr3(1 0)
 STA BDdataptr1         ;
 LDA BDdataptr4         ; So this sets the data pointer in BDdataptr1(1 0) back
 STA BDdataptr2         ; to the original value that we gave it at the start of
                        ; the BDENTRY routine when we started playing this tune,
                        ; which we stored in BDdataptr3(1 0)
                        ;
                        ; In other words, this restarts the current tune

 JMP BDskip1            ; Jump to BDskip1 to process the next nibble of music
                        ; data

[X]

Variable BDBUFF in workspace ZP

The music data byte that is currently being processed, with the low nibble being processed first, and then the high nibble

[X]

Variable BDdataptr1 in workspace ZP

The low byte of the address of the music data pointer in BDdataptr1(1 0), which points to the end of the music data currently being processed

[X]

Variable BDdataptr2 in workspace ZP

The high byte of the address of the music data pointer in BDdataptr1(1 0), which points to the end of the music data currently being processed

[X]

Variable BDdataptr3 in workspace ZP

The low byte of the address of the music data pointer in BDdataptr3(1 0), which is a backup of the initial value of the BDdataptr1(1 0) pointer, so music can be repeated

[X]

Variable BDdataptr4 in workspace ZP

The high byte of the address of the music data pointer in BDdataptr3(1 0), which is a backup of the initial value of the BDdataptr1(1 0) pointer, so music can be repeated

[X]

Entry point BDskip1 in subroutine BDirqhere (category: Sound)

Process the next nibble of music data in BDBUFF

Sound: BDRO9

[Commodore 64 version]