Sound: coffee

       Name: coffee                                                  [Show more]
       Type: Subroutine
   Category: Sound
    Summary: Return from the interrupt routine, for when we are making sound
             effects
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * COMIRQ1 calls coffee


.coffee

 PLA                    ; Retrieve the value of Y we stored on the stack at the
 TAY                    ; start of the music section of the interrupt routine,
                        ; so it is preserved

 PLA                    ; Retrieve the value of X we stored on the stack at the
 TAX                    ; start of the interrupt routine, so it is preserved

 LDA l1                 ; Set bits 0 to 2 of the port register at location l1
 AND #%11111000         ; ($0001) to bits 0 to 2 of L1M, leaving bits 3 to 7
 ORA L1M                ; unchanged
 STA l1                 ;
                        ; This sets LORAM, HIRAM and CHAREN to the values in
                        ; L1M, which ensures we return memory to the same
                        ; configuration as when we entered the interrupt routine

 PLA                    ; Retrieve the value of A we stored on the stack at the
                        ; start of the interrupt routine, so it is preserved

 RTI                    ; Return from the interrupt