diff options
Diffstat (limited to 'basics')
| -rw-r--r-- | basics/sprite.s | 13 |
1 files changed, 7 insertions, 6 deletions
diff --git a/basics/sprite.s b/basics/sprite.s index 09dd8e5..fc024f7 100644 --- a/basics/sprite.s +++ b/basics/sprite.s @@ -185,10 +185,11 @@ reset: inx bne @ram_reset_loop ; if x overflows back to #00, then we are done. - ;; And now another thing we can do is to reset the sprites. In NES programs - ;; sprites live in a special range of memory addresses from the RAM called - ;; OAM (Object Attribute Memory). This range is located in $0200-02ff (the - ;; range we did not initialize when cleaning up RAM). + ;; And now another thing we can do is to reset the sprites. We will reserve + ;; space for sprites in $0200-02ff (the range we did not initialize when + ;; cleaning up RAM). With this in mind we will perform a DMA process right + ;; after this block of code that will take this memory range and bulk it + ;; into PPU OAM space. ;; ;; "Resetting sprites" is just a matter of giving them a value which will ;; not bother us in the future. One way to do this is to set each value to @@ -209,8 +210,8 @@ reset: ;; the byte given at the OAMADDR, thus XX = #$00; and N = 2 (see `lda ;; #$02`). Therefore, we are telling the PPU to start the DMA process from ;; $200. The PPU will assume that the following 256 bytes of memory are the - ;; ones to be copied, resulting in a DMA copy of $200-$2ff, right where the - ;; sprite data is located in memory. + ;; ones to be copied, resulting in a DMA copy of $200-$2ff, right where we + ;; stored the sprite data in advance. lda #$00 sta $2003 ; OAMADDR lda #$02 |