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⌂ ∞ Elite on the BBC Micro and NES

PPU: WaitForPPUToFinish

[NES version, Bank 7]

       Name: WaitForPPUToFinish                                      [Show more]
       Type: Subroutine
   Category: PPU
    Summary: Wait until the NMI handler has finished updating both bitplanes,
             so the screen is no longer refreshing

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * BuyAndSellCargo calls WaitForPPUToFinish
             * DrawMessageInNMI calls WaitForPPUToFinish
             * DrawScreenInNMI calls WaitForPPUToFinish
             * DrawScrollInNMI calls WaitForPPUToFinish
             * FadeToBlack calls WaitForPPUToFinish
             * HighlightLaserView calls WaitForPPUToFinish
             * LL164 calls WaitForPPUToFinish
             * PAUSE calls WaitForPPUToFinish
             * PauseGame calls WaitForPPUToFinish
             * SetupViewInNMI calls WaitForPPUToFinish
             * TT66 calls WaitForPPUToFinish
             * UpdateEquipment calls WaitForPPUToFinish
             * UpdateSaveScreen calls WaitForPPUToFinish




.WaitForPPUToFinish

 SETUP_PPU_FOR_ICON_BAR ; If the PPU has started drawing the icon bar, configure
                        ; the PPU to use nametable 0 and pattern table 0

 LDA bitplaneFlags      ; Keep looping back to the start of the routine until
 AND #%01000000         ; bit 6 of the bitplane flags for bitplane 0 is clear
 BNE WaitForPPUToFinish

 LDA bitplaneFlags+1    ; Do the same for bitplane 1
 AND #%01000000
 BNE WaitForPPUToFinish

                        ; We get here when both bitplanes have bit 6 clear,
                        ; which means neither bitplane is configured to send
                        ; nametable data to the PPU
                        ;
                        ; This means the screen has finished refreshing and
                        ; there is no longer any nametable data that needs
                        ; sending to the PPU, so we can return from the
                        ; subroutine

 RTS                    ; Return from the subroutine