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⌂ ∞ Elite on the BBC Micro and NES

PPU: SendInventoryToPPU

[NES version, Bank 7]

       Name: SendInventoryToPPU                                      [Show more]
       Type: Subroutine
   Category: PPU
    Summary: Send X batches of 16 bytes from SC(1 0) to the PPU, for sending
             the inventory icon bar image

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * SendViewToPPU calls SendInventoryToPPU




 Arguments:

   X                    The number of batches of 16 bytes to send to the PPU

   SC(1 0)              The address of the data to send



.SendInventoryToPPU

 LDY #0                 ; Set Y as an index counter for the following block,
                        ; which sends 16 bytes of data from SC(1 0) to the PPU,
                        ; using Y as an index that starts at 0 and increments
                        ; after each byte
                        ;
                        ; We repeat this process for X iterations

                        ; We repeat the following code 16 times, so it sends
                        ; one whole pattern of 16 bytes to the PPU (eight bytes
                        ; for each bitplane)

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA (SC),Y             ; Send the Y-th byte of SC(1 0) to the PPU and increment
 STA PPU_DATA           ; the index in Y
 INY

 LDA SC                 ; Set SC(1 0) = SC(1 0) + 16
 CLC                    ;
 ADC #16                ; Starting with the low bytes
 STA SC

 BCC smis1              ; And then the high bytes
 INC SC+1

.smis1

 DEX                    ; Decrement the block counter in X

 BNE SendInventoryToPPU ; Loop back to the start of the subroutine until we have
                        ; sent X batches of 16 bytes

 RTS                    ; Return from the subroutine