From 98223d9e5a03c8de93f3af95ea822f4f2f7bbf71 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Fri, 21 Oct 2022 05:12:50 -0300
Subject: [PATCH] chore: implement more than just 1 cycle per mem access

---
 src/Bus.zig | 17 +++++++++++++++--
 src/cpu.zig |  4 ++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/Bus.zig b/src/Bus.zig
index d678170..db284e9 100644
--- a/src/Bus.zig
+++ b/src/Bus.zig
@@ -21,6 +21,19 @@ const log = std.log.scoped(.Bus);
 const createDmaTuple = @import("bus/dma.zig").create;
 const createTimerTuple = @import("bus/timer.zig").create;
 const rotr = @import("util.zig").rotr;
+
+const timings: [2][0x10]u8 = [_][0x10]u8{
+    // BIOS, Unused, EWRAM, IWRAM, I/0, PALRAM, VRAM, OAM, ROM0, ROM0, ROM1, ROM1, ROM2, ROM2, SRAM, Unused
+    [_]u8{ 1, 1, 3, 1, 1, 1, 1, 1, 5, 5, 5, 5, 5, 5, 5, 5 }, // 8-bit & 16-bit
+    [_]u8{ 1, 1, 6, 1, 1, 2, 2, 1, 8, 8, 8, 8, 8, 8, 8, 8 }, // 32-bit
+};
+
+pub const fetch_timings: [2][0x10]u8 = [_][0x10]u8{
+    // BIOS, Unused, EWRAM, IWRAM, I/0, PALRAM, VRAM, OAM, ROM0, ROM0, ROM1, ROM1, ROM2, ROM2, SRAM, Unused
+    [_]u8{ 1, 1, 3, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 5, 5 }, // 8-bit & 16-bit
+    [_]u8{ 1, 1, 6, 1, 1, 2, 2, 1, 4, 4, 4, 4, 4, 4, 8, 8 }, // 32-bit
+};
+
 const Self = @This();
 
 pak: GamePak,
@@ -112,7 +125,7 @@ fn readBios(self: *Self, comptime T: type, address: u32) T {
 pub fn read(self: *Self, comptime T: type, address: u32) T {
     const page = @truncate(u8, address >> 24);
     const align_addr = alignAddress(T, address);
-    self.sched.tick += 1;
+    defer self.sched.tick += timings[@boolToInt(T == u32)][@truncate(u4, page)];
 
     return switch (page) {
         // General Internal Memory
@@ -147,7 +160,7 @@ pub fn read(self: *Self, comptime T: type, address: u32) T {
 pub fn write(self: *Self, comptime T: type, address: u32, value: T) void {
     const page = @truncate(u8, address >> 24);
     const align_addr = alignAddress(T, address);
-    self.sched.tick += 1;
+    defer self.sched.tick += timings[@boolToInt(T == u32)][@truncate(u4, page)];
 
     switch (page) {
         // General Internal Memory
diff --git a/src/cpu.zig b/src/cpu.zig
index a61042a..94e1cb6 100644
--- a/src/cpu.zig
+++ b/src/cpu.zig
@@ -330,6 +330,10 @@ pub const Arm7tdmi = struct {
         comptime std.debug.assert(T == u32 or T == u16); // Opcode may be 32-bit (ARM) or 16-bit (THUMB)
         defer self.r[15] += if (T == u32) 4 else 2;
 
+        // FIXME: You better hope this is optimized out
+        const tick_cache = self.sched.tick;
+        defer self.sched.tick = tick_cache + Bus.fetch_timings[@boolToInt(T == u32)][@truncate(u4, self.r[15] >> 24)];
+
         return self.bus.read(T, self.r[15]);
     }