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⌂ ∞ ▽ Elite on the BBC Micro and NES

PPU: SendPatternsToPPU (Part 6 of 6)

[NES version, Bank 7]

       Name: SendPatternsToPPU (Part 6 of 6)                         [Show more]
       Type: Subroutine
   Category: PPU
    Summary: Save progress for use in the next VBlank and return from the
             subroutine
  Deep dive: Drawing vector graphics using NES tiles

    Context: See this subroutine in context in the source code
 References: No direct references to this subroutine in this source file




.spat30

                        ; We now store the following variables, so they can be
                        ; picked up when we return in the next VBlank:
                        ;
                        ;   * (patternBufferHi patternBufferLo)
                        ;
                        ;   * sendingPattern

 STX patternCounter     ; Store X in patternCounter to use below

 LDX nmiBitplane        ; Set (patternBufferHi patternBufferLo) for this
 STY patternBufferLo,X  ; bitplane to dataForPPU(1 0) + Y (which is the address
 LDA dataForPPU+1       ; of the next byte of data to be sent from the pattern
 STA patternBufferHi,X  ; buffer in the next VBlank)

 LDA patternCounter     ; Set sendingPattern for this bitplane to the value of
 STA sendingPattern,X   ; X we stored above (which is the number / 8 of the next
                        ; pattern to be sent from the pattern buffer in the next
                        ; VBlank)

 JMP RTS1               ; Return from the subroutine (as RTS1 contains an RTS)