From 951c7f3a146359b501abc712a09a8113cfd1a8a2 Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Tue, 13 Apr 2021 18:28:56 +0200
Subject: Update initial example w/ utility macros/functions

The initial implementation was very obtuse. Using macros for different
areas of GBA memory and some other utilities will make it much easier to
understand.
---
 src/main.c      | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 src/shorthand.h | 36 ++++++++++++++++++++++++++
 2 files changed, 109 insertions(+), 7 deletions(-)
 create mode 100644 src/shorthand.h

diff --git a/src/main.c b/src/main.c
index 655373b..88f4f4e 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,12 +1,78 @@
-int main()
-{
-    *(unsigned int*)0x04000000 = 0x0403;
+#include "shorthand.h"
 
-    ((unsigned short*)0x06000000)[120+80*240] = 0x001F;
-    ((unsigned short*)0x06000000)[136+80*240] = 0x03E0;
-    ((unsigned short*)0x06000000)[120+96*240] = 0x7C00;
+//
+// Memory sections.
+//
 
-    while(1);
+// Defines for the different memory sections in the GBA.
+#define MEM_SROM  0x00000000
+#define MEM_EW    0x02000000
+#define MEM_IW    0x03000000
+#define MEM_IO    0x04000000
+#define MEM_PAL   0x05000000
+#define MEM_VRAM  0x06000000
+#define MEM_OAM   0x07000000
+#define MEM_PAK   0x08000000
+#define MEM_CART  0x0E000000
+
+//
+// Display modes.
+//
+
+// Screen settings.
+#define SCREEN_WIDTH 240
+#define SCREEN_HEIGHT 160
+
+// Display modes.
+#define DISP_MODE_0 0x0000
+#define DISP_MODE_1 0x0001
+#define DISP_MODE_2 0x0002
+#define DISP_MODE_3 0x0003
+#define DISP_MODE_4 0x0004
+#define DISP_MODE_5 0x0005
+
+// Layers.
+#define DISP_BG0 0x0100
+#define DISP_BG1 0x0200
+#define DISP_BG2 0x0400
+#define DISP_BG3 0x0800
+#define DISP_OBJ 0x1000
+
+static inline void
+set_display_mode(u16 value) {
+    *((volatile u32*)(MEM_IO + 0x0000)) = value;
+}
+
+//
+// Colors.
+//
+
+// The GBA in mode 3 expects rbg15 colors in the VRAM, where each component
+// (RGB) have a 0--31 range. For example, pure red would be rgb15(31, 0, 0).
+typedef u16 Color;
+
+static inline Color
+rgb15(u32 red, u32 green, u32 blue ) {
+    return (blue << 10) | (green << 5) | red;
+}
+
+static inline void
+put_pixel(int x, int y, Color clr) {
+    ((volatile u16*)MEM_VRAM)[x + y * SCREEN_WIDTH] = clr;
+}
+
+//
+// Main functions.
+//
+
+int main(void) {
+    set_display_mode(DISP_MODE_3 | DISP_BG2);
+
+    put_pixel(120 , 80, rgb15(31, 0, 0));
+    put_pixel(136 , 80, rgb15(0, 31, 0));
+    put_pixel(120 , 96, rgb15(0, 0, 31));
+
+    while(true);
 
     return 0;
 }
diff --git a/src/shorthand.h b/src/shorthand.h
new file mode 100644
index 0000000..42eb935
--- /dev/null
+++ b/src/shorthand.h
@@ -0,0 +1,36 @@
+#ifndef UTILS_SHORTHAND_H
+#define UTILS_SHORTHAND_H
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+//
+// This simple header just typedefs the basic C define types to a shorter name,
+// loads the quality of life bool macro for _Bool and defines shorthand macros
+// for byte sizes.
+
+typedef uint8_t      u8;
+typedef uint16_t     u16;
+typedef uint32_t     u32;
+typedef uint64_t     u64;
+typedef int8_t       s8;
+typedef int16_t      s16;
+typedef int32_t      s32;
+typedef int64_t      s64;
+typedef volatile u8  vu8;
+typedef volatile u16 vu16;
+typedef volatile u32 vu32;
+typedef volatile u64 vu64;
+typedef volatile s8  vs8;
+typedef volatile s16 vs16;
+typedef volatile s32 vs32;
+typedef volatile s64 vs64;
+
+#define KB(N) ((u64)(N)   * 1024)
+#define MB(N) ((u64)KB(N) * 1024)
+#define GB(N) ((u64)MB(N) * 1024)
+#define TB(N) ((u64)GB(N) * 1024)
+
+#endif // UTILS_SHORTHAND_H
-- 
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