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⌂ ∞ Elite on the BBC Micro and NES

Icon bar: UpdateIconBar

[NES version, Bank 3]

       Name: UpdateIconBar                                           [Show more]
       Type: Subroutine
   Category: Icon bar
    Summary: Update the icon bar
  Deep dive: Views and view types in NES Elite

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * UpdateIconBar_b3 calls UpdateIconBar




.UpdateIconBar

 LDA iconBarType        ; Set A to the current icon bar type

 JSR SetupIconBar       ; Set up the icon bar

 LDA QQ11               ; If bit 6 of the view type is set, then there is no
 AND #%01000000         ; icon bar on the screen, so jump to ubar2 to return
 BNE ubar2              ; from the subroutine as there is no icon bar to update

 JSR SetIconBarRow      ; Set the row on which the icon bar appears, which
                        ; depends on the view type

 LDA #%10000000         ; Set bit 7 of skipBarPatternsPPU, so the NMI handler
 STA skipBarPatternsPPU ; only sends the nametable entries and not the tile
                        ; patterns

 ASL A                  ; Set barPatternCounter = 0, so the NMI handler sends
 STA barPatternCounter  ; icon bar data to the PPU

.ubar1

 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 barPatternCounter  ; Loop back to keep the PPU configured in this way until
 BPL ubar1              ; barPatternCounter is set to 128
                        ;
                        ; This happens when the NMI handler has finished sending
                        ; all the icon bar's nametable entries to the PPU, so
                        ; this loop keeps the PPU configured to use nametable 0
                        ; and pattern table 0 until the icon bar nametable
                        ; entries have been sent

 ASL skipBarPatternsPPU ; Set skipBarPatternsPPU = 0, so the NMI handler goes
                        ; back to sending both nametable entries and tile
                        ; patterns for the icon bar (when barPatternCounter is
                        ; non-zero)

.ubar2

 RTS                    ; Return from the subroutine