From f923f9fecb58b7e8f45c0d14203ddbc01cd8749f Mon Sep 17 00:00:00 2001
From: Lukas Krickl <lukas@krickl.dev>
Date: Tue, 1 Oct 2024 10:05:20 +0200
Subject: [PATCH] Initial setup for engine

---
 src/jmp.inc    |  2 +-
 src/macros.inc |  3 +++
 src/main.s     | 10 ++++++++++
 src/mem.s      | 46 +++++++++++++++++++++++++++++++++++++++++++++-
 src/oam.s      |  7 +++++++
 src/strings.s  | 11 +++++++++++
 src/sys.s      | 18 ++++++++++++++++++
 src/video.s    | 10 +++++++++-
 src/wram.s     |  7 +++++++
 9 files changed, 111 insertions(+), 3 deletions(-)
 create mode 100644 src/oam.s
 create mode 100644 src/strings.s
 create mode 100644 src/sys.s
 create mode 100644 src/wram.s

diff --git a/src/jmp.inc b/src/jmp.inc
index 2a8501d..f6f0d18 100644
--- a/src/jmp.inc
+++ b/src/jmp.inc
@@ -15,7 +15,7 @@ rst_panic:
 ;=============
 vec_vblank:
   push_all 
-  
+  call vblank  
   pop_all
 
   reti
diff --git a/src/macros.inc b/src/macros.inc
index b4e7f0c..e768638 100644
--- a/src/macros.inc
+++ b/src/macros.inc
@@ -11,3 +11,6 @@
   pop bc
   pop af
 #endmacro
+
+; relative jump: jr <label> RELB 
+#define REL - $ - 2 & 0xFF 
diff --git a/src/main.s b/src/main.s
index 870aafc..604bbc4 100644
--- a/src/main.s
+++ b/src/main.s
@@ -1,5 +1,7 @@
 #include "hw.inc"
 #include "macros.inc"
+#include "oam.s"
+#include "wram.s"
 
 .org 0x0
 #include "jmp.inc"
@@ -7,10 +9,16 @@
 #include "header.inc"
  
 entry: 
+  call disableinterrutpts
+  
+  call mem_init 
+
   call lcd_off
   call copy_tiles
   call lcd_on
 
+  call enableinterrupts
+
 main:
 @forever:
   jp @forever 
@@ -18,6 +26,8 @@ main:
 #include "tiles.inc"
 #include "video.s"
 #include "mem.s"
+#include "strings.s"
+#include "sys.s"
 
 ; fill bank
 .fill 0, 0x7FFF - $
diff --git a/src/mem.s b/src/mem.s
index 97315cc..4a9dbdd 100644
--- a/src/mem.s
+++ b/src/mem.s
@@ -1,10 +1,24 @@
+mem_init:
+ ; clear wram
+  ld a, 0
+  ld hl, WRAM
+  ld bc, WRAMLEN
+  call memset
+
+  ; copy shadow oam dma function 
+  ld de, shadow_oam_to_oam 
+  ld hl, OAMDMAFN
+  ld bc, shadow_oam_to_oam_end - shadow_oam_to_oam 
+  call memcpy
+  ret
+
 ; copies memory from one location to another 
 ; inputs:
 ;   de: source
 ;   hl: destination
 ;   bc: length
 memcpy:
-  @loop:
+@loop:
   ld a, [de]
   ld [hl+], a
 
@@ -15,3 +29,33 @@ memcpy:
   jp nz, @loop
 
   ret
+
+  ; sets a memory location to a specific value 
+  ; inputs:
+  ;   hl: destination
+  ;   bc: length
+  ;    d: value 
+memset:
+@loop:
+  ld a, d
+  ld [hl+], a
+
+  dec bc
+  ld a, b
+  or a, c
+  jp nz, @loop
+  ret
+
+
+; dma shadow oam to oam
+; registers:
+;   hl, af, bc, de
+shadow_oam_to_oam:
+  ld a, shadow_oam >> 8  
+  ldh [DMA], a
+  ld a, 40 ; 160-cycle wait 
+@wait:
+  dec a
+  jr nz, @wait REL
+  ret 
+shadow_oam_to_oam_end:
diff --git a/src/oam.s b/src/oam.s
new file mode 100644
index 0000000..b71df91
--- /dev/null
+++ b/src/oam.s
@@ -0,0 +1,7 @@
+; oam memory layout 
+.se 0
+.de oamy, 1
+.de oamx, 1
+.de oamchr, 1
+.de oamflag, 1
+.de oamsize, 0
diff --git a/src/strings.s b/src/strings.s
new file mode 100644
index 0000000..eecbd24
--- /dev/null
+++ b/src/strings.s
@@ -0,0 +1,11 @@
+; map ascii values to the actual tileset here
+.rep i, 10, 1, .scc i + '0' = i
+.rep i, 26, 1, .scc i + 'a' = i + 10
+.rep i, 26, 1, .scc i + 'A' = i + 10
+
+; map space to empty tile
+.scc 0x20 = 0x30
+
+STR_TITLE:
+.str "game"
+.db 0
diff --git a/src/sys.s b/src/sys.s
new file mode 100644
index 0000000..f058b4b
--- /dev/null
+++ b/src/sys.s
@@ -0,0 +1,18 @@
+nohandler:
+  ret
+
+panic:
+  ret
+
+enableinterrupts:
+  ; enable interrupts 
+  ld a, IVBLANK
+  ld [IE], a
+  ei 
+  ret
+
+disableinterrutpts:
+  ld a, 0
+  ld [IE], a
+  di
+  ret
diff --git a/src/video.s b/src/video.s
index 5601141..7aa2bf9 100644
--- a/src/video.s
+++ b/src/video.s
@@ -1,3 +1,9 @@
+; vblank handler
+vblank:
+  call OAMDMAFN
+
+  ret
+
 vblank_wait:
   ld a, [RLY] 
   cp a, 144
@@ -15,11 +21,13 @@ lcd_off:
   ret
 
 lcd_on:
-  ld a, LCDCF_ON | LCDCF_BGON
+  ld a, LCDCF_ON | LCDCF_BGON | LCDCF_OBJON 
   ld [RLCD], a
 
   ret
 
+  ; copies tilest0 and tileset1 to
+  ; vram
 copy_tiles:
   ld de, tileset0
   ld hl, VRAM 
diff --git a/src/wram.s b/src/wram.s
new file mode 100644
index 0000000..589dcfa
--- /dev/null
+++ b/src/wram.s
@@ -0,0 +1,7 @@
+#define WRAM 0xC000
+#define WRAMLEN 0xFFF
+.org WRAM
+
+.def int OAMDMAFN = 0xFF80 
+
+shadow_oam: .adv OBJSMAX * oamsize 
-- 
2.30.2