diff options
Diffstat (limited to 'fx/blink.s')
| -rw-r--r-- | fx/blink.s | 33 |
1 files changed, 18 insertions, 15 deletions
@@ -5,7 +5,7 @@ ;; https://www.nesdev.org/wiki/MMC3. The MMC3 is a pretty advanced chip, so ;; first go over the `basics/` directory for a better understanding on easier ;; topics. Most importantly, take a look at examples like `basics/persist.s` or -;; `basics/unrom`, which also perform bank switching albeit with simpler +;; `basics/unrom.s`, which also perform bank switching albeit with simpler ;; hardware. ;; ;; This example basically makes use of the bank switching capabilities of the @@ -41,8 +41,8 @@ ;; Variables used on this example. .scope Vars - counter = $00 - last_bank = $01 + zp_counter = $00 + zp_last_bank = $01 .endscope .segment "HEADER" @@ -128,14 +128,14 @@ ;;; specific to this example. .segment "TAIL" -reset: +.proc reset sei cld ldx #$40 stx $4017 - ldx #$ff + ldx #$FF txs inx @@ -217,7 +217,7 @@ reset: inx bne @ram_reset_loop - lda #$ef + lda #$EF @sprite_reset_loop: sta $200, x inx @@ -244,6 +244,7 @@ reset: dex bne @palettes_reset_loop jmp main +.endproc ;;; NOTE: mainly as usual except that a bit of game loop has been added to ;;; handle the blinking state. @@ -251,7 +252,7 @@ reset: ;; The code will iterate between banks 4 and 6 on the pattern table, as ;; that's where sprites are located (check the CHARS segment for more info). lda #4 - sta Vars::last_bank + sta Vars::zp_last_bank CLEAR_SCREEN @@ -289,13 +290,13 @@ reset: ;; NOTE: let there be a game logic :D ;; Is the counter already at the limit? If not just restart the game loop. - lda Vars::counter + lda Vars::zp_counter cmp #$20 bne @main_game_loop ;; Reset the counter lda #0 - sta Vars::counter + sta Vars::zp_counter ;; The whole trick is done on R2, which points to $1000, where the sprite ;; tiles begin. Hence, select it. @@ -303,7 +304,7 @@ reset: sta MMC3::BANK_SELECT ;; The value for the register is either 4 or 6 depending on its last value. - lda Vars::last_bank + lda Vars::zp_last_bank cmp #4 beq :+ lda #4 @@ -312,7 +313,7 @@ reset: lda #6 @set: ;; Save which is the bank being used both internally and onto the MMC3 chip. - sta Vars::last_bank + sta Vars::zp_last_bank sta MMC3::BANK_DATA jmp @main_game_loop @@ -346,7 +347,7 @@ initial_sprite_data: ;;; NOTE: nothing to highlight here other than the counter is increased on each ;;; NMI. -nmi: +.proc nmi bit $20 bpl @next @@ -357,7 +358,7 @@ nmi: pha ;; Increase the counter for the blinking. - inc Vars::counter + inc Vars::zp_counter jsr Diskun::nmi_update @@ -382,10 +383,12 @@ nmi: pla @next: rti +.endproc ;;; NOTE: IRQ is disabled when setting up the MMC3 chip for this example. -irq: +.proc irq rti +.endproc ;;; NOTE: The header for this game advertises 128KB for CHR-ROM. This is wildly ;;; too much for this example, but it's a reasonable size for an MMC3 game. @@ -402,7 +405,7 @@ irq: ;; filled with `diskun0.chr` and `diskun1.chr`, which are 2KB each. Hence, the ;; 4th CHR bank contains the regular character, and the 6th CHR bank contains ;; the blinking version. You can see these values used when initializing -;; `Vars::last_bank`, or when performing bank switching. +;; `Vars::zp_last_bank`, or when performing bank switching. .res $1000, $00 .incbin "../assets/diskun0.chr" ; First half of the second pattern table has the default diskun character. .incbin "../assets/diskun1.chr" ; Second half of the second pattern table simply has the blinking version. |