Utility routines: WaitFor3xVBlank

       Name: WaitFor3xVBlank                                         [Show more]
       Type: Subroutine
   Category: Utility routines
    Summary: Wait for three VBlanks to pass
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * ResetScreen calls WaitFor3xVBlank


.WaitFor3xVBlank

 LDA PPU_STATUS         ; Read the PPU_STATUS register, which clears the VBlank
                        ; latch in bit 7, so the following loops will wait for
                        ; three VBlanks in total

.wait1

 LDA PPU_STATUS         ; Wait for the first VBlank to pass, which will set bit
 BPL wait1              ; 7 of PPU_STATUS (and reading PPU_STATUS clears bit 7,
                        ; ready for the next VBlank)

.wait2

 LDA PPU_STATUS         ; Wait for the second VBlank to pass
 BPL wait2

                        ; Fall through into WaitForVBlank to wait for the third
                        ; VBlank before returning from the subroutine