space: Simplify the code and its goals

Originally this was supposed to be a sort of mini game, but that would
have probably made it too complex for newcomers. Thus, let's just keep
it to subpixel movement and shooting bullets, which is already a big
step from the `basics/sprite.s` example.

Signed-off-by: Miquel Sabaté Solà <msabate@suse.com>

1 files changed, 10 insertions, 37 deletions

diff --git a/space/src/vectors/reset.s b/space/src/vectors/reset.s
index afc9fa5..1216146 100644
--- a/space/src/vectors/reset.s
+++ b/space/src/vectors/reset.s
@@ -1,39 +1,25 @@
 .segment "CODE"
 
+;; Check `basics/sprite.s` for a deeper look on the logic below. I have only
+;; added code after configuration/reset is done.
 reset:
-    ;; Ignore IRQs and disable decimal mode.
     sei
     cld
-
-    ;; Disable APU frame IRQ.
     ldx #$40
-    stx APU::FRAME_COUNTER
+    stx $4017
 
-    ;; Set up the stack register with the proper value.
     ldx #$ff
     txs
 
-    ;; And now disable, in this order, NMI, rendering and DMC IRQs. Note that
-    ;; `x` was set to $ff, so increasing it by one results in a zero, which is
-    ;; the value then stored in the aforementioned memory locations.
     inx
-    stx PPU::CONTROL
-    stx PPU::MASK
-    stx APU::DMC
-
-    ;;;
-    ;; NOTE: If you are using a mapper which needs some special configuration,
-    ;; now it would be a good time set it up. I am not using a special mapper,
-    ;; so there's nothing from me to do here.
-    ;;;
+    stx $2000
+    stx $2001
+    stx $4010
 
-    ;; First of the two VBLANK waits.
 @vblankwait1:
-    bit PPU::STATUS
+    bit $2002
     bpl @vblankwait1
 
-    ;; Clear RAM memory. Notice that we are not clearing $200-$2ff, this is done
-    ;; later.
     ldx #0
     lda #0
 @ram_reset_loop:
@@ -47,30 +33,17 @@ reset:
     inx
     bne @ram_reset_loop
 
-    ;; Reset sprites by moving them off-screen.
     lda #$ef
 @sprite_reset_loop:
     sta $200, x
     inx
     bne @sprite_reset_loop
 
-    ;; Write "sprites" into OAM.
-    OAM_WRITE_SPRITES
-
-    ;; Last VBLANK wait.
 @vblankwait2:
-    bit PPU::STATUS
+    bit $2002
     bpl @vblankwait2
 
-    ;; Reset palettes.
-    PPU_ADDR $3F00
-
-    lda #$0F
-    ldx #$20
-@palettes_reset_loop:
-    sta PPU::DATA
-    dex
-    bne @palettes_reset_loop
+    ;;;
+    ;; NOTE: configuration/reset is done, the code below is our actual program :D
 
-    ;; Jump into the main subroutine.
     jmp main