From c660ca8922da3db3d5589ca4d86bb89486a6fcd9 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Wed, 29 Dec 2021 17:16:32 -0600
Subject: [PATCH] feat: implement LDR STR

---
 src/bus.zig                      |  9 +++++++--
 src/cpu.zig                      |  4 ++--
 src/cpu/single_data_transfer.zig | 10 ++++++++--
 src/pak.zig                      |  7 +++++++
 4 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/src/bus.zig b/src/bus.zig
index 03c12ab..2a41c37 100644
--- a/src/bus.zig
+++ b/src/bus.zig
@@ -16,8 +16,13 @@ pub const Bus = struct {
         return self.pak.readWord(addr);
     }
 
-    pub fn writeWord(_: *@This(), _: u32, _: u32) void {
-        std.debug.panic("TODO: Implement Bus#writeWord", .{});
+    pub fn writeWord(self: *@This(), addr: u32, word: u32) void {
+        // TODO: Actually implement the memory mmap
+        if (addr >= self.pak.buf.len) {
+            return;
+        }
+
+        self.pak.writeWord(addr, word);
     }
 
     pub fn readHalfWord(self: *const @This(), addr: u32) u16 {
diff --git a/src/cpu.zig b/src/cpu.zig
index dbb758a..97cb45c 100644
--- a/src/cpu.zig
+++ b/src/cpu.zig
@@ -27,8 +27,8 @@ pub const ARM7TDMI = struct {
 
     pub inline fn step(self: *@This()) u64 {
         const opcode = self.fetch();
-        // Debug
-        std.debug.print("R15: 0x{X:}\n", .{opcode});
+
+        std.debug.print("R15: 0x{X:}\n", .{opcode}); // Debug
 
         ARM_LUT[armIdx(opcode)](self, self.bus, opcode);
 
diff --git a/src/cpu/single_data_transfer.zig b/src/cpu/single_data_transfer.zig
index 468c15c..1d107dd 100644
--- a/src/cpu/single_data_transfer.zig
+++ b/src/cpu/single_data_transfer.zig
@@ -24,7 +24,9 @@ pub fn comptimeSingleDataTransfer(comptime I: bool, comptime P: bool, comptime U
                     cpu.r[rd] = bus.readByte(address);
                 } else {
                     // LDR
-                    std.debug.panic("Implement LDR", .{});
+
+                    // FIXME: Unsure about how I calculate the boundary offset
+                    cpu.r[rd] = std.math.rotl(u32, bus.readWord(address), address % 4);
                 }
             } else {
                 if (B) {
@@ -37,7 +39,11 @@ pub fn comptimeSingleDataTransfer(comptime I: bool, comptime P: bool, comptime U
                     bus.writeByte(address, src);
                 } else {
                     // STR
-                    std.debug.panic("Implement STR", .{});
+
+                    // FIXME: Is this right?
+                    const src = cpu.r[rd];
+                    const aligned_addr = address - (address % 4);
+                    bus.writeWord(aligned_addr, src);
                 }
             }
 
diff --git a/src/pak.zig b/src/pak.zig
index 1e77b85..f16ca3c 100644
--- a/src/pak.zig
+++ b/src/pak.zig
@@ -20,6 +20,13 @@ pub const GamePak = struct {
         return (@as(u32, self.buf[addr + 3]) << 24) | (@as(u32, self.buf[addr + 2]) << 16) | (@as(u32, self.buf[addr + 1]) << 8) | (@as(u32, self.buf[addr]));
     }
 
+    pub fn writeWord(self: *const @This(), addr: u32, word: u32) void {
+        self.buf[addr + 3] = @truncate(u8, word >> 24);
+        self.buf[addr + 2] = @truncate(u8, word >> 16);
+        self.buf[addr + 1] = @truncate(u8, word >> 8);
+        self.buf[addr] = @truncate(u8, word);
+    }
+
     pub fn readHalfWord(self: *const @This(), addr: u32) u16 {
         return (@as(u16, self.buf[addr + 1]) << 8) | @as(u16, self.buf[addr]);
     }