From ca41f6a85c661a9a61946aaaa2a5ffce3089a60f Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Tue, 1 Feb 2022 17:56:11 -0400
Subject: [PATCH] feat(cpu): implement format 10 THUMB instructions

---
 src/cpu.zig                |  8 ++++++++
 src/cpu/thumb/format10.zig | 24 ++++++++++++++++++++++++
 2 files changed, 32 insertions(+)
 create mode 100644 src/cpu/thumb/format10.zig

diff --git a/src/cpu.zig b/src/cpu.zig
index 0374583..f2d6953 100644
--- a/src/cpu.zig
+++ b/src/cpu.zig
@@ -27,6 +27,7 @@ const format4 = @import("cpu/thumb/format4.zig").format4;
 const format5 = @import("cpu/thumb/format5.zig").format5;
 const format6 = @import("cpu/thumb/format6.zig").format6;
 const format9 = @import("cpu/thumb/format9.zig").format9;
+const format10 = @import("cpu/thumb/format10.zig").format10;
 const format12 = @import("cpu/thumb/format12.zig").format12;
 const format13 = @import("cpu/thumb/format13.zig").format13;
 const format14 = @import("cpu/thumb/format14.zig").format14;
@@ -373,6 +374,13 @@ fn thumbPopulate() [0x400]ThumbInstrFn {
                 lut[i] = format6(rd);
             }
 
+            if (i >> 6 & 0xF == 0b1000) {
+                const L = i >> 5 & 1 == 1;
+                const offset = i & 0x1F;
+
+                lut[i] = format10(L, offset);
+            }
+
             if (i >> 7 & 0x7 == 0b011) {
                 const B = i >> 6 & 1 == 1;
                 const L = i >> 5 & 1 == 1;
diff --git a/src/cpu/thumb/format10.zig b/src/cpu/thumb/format10.zig
new file mode 100644
index 0000000..fef8198
--- /dev/null
+++ b/src/cpu/thumb/format10.zig
@@ -0,0 +1,24 @@
+const std = @import("std");
+
+const Bus = @import("../../Bus.zig");
+const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
+const InstrFn = @import("../../cpu.zig").ThumbInstrFn;
+
+pub fn format10(comptime L: bool, comptime offset: u5) InstrFn {
+    return struct {
+        fn inner(cpu: *Arm7tdmi, bus: *Bus, opcode: u16) void {
+            const rb = opcode >> 3 & 0x7;
+            const rd = opcode & 0x7;
+
+            const address = cpu.r[rb] + (offset << 1);
+
+            if (L) {
+                // LDRH
+                cpu.r[rd] = bus.read16(address & 0xFFFF_FFFE);
+            } else {
+                // STRH
+                bus.write16(address & 0xFFFF_FFFE, @truncate(u16, cpu.r[rd]));
+            }
+        }
+    }.inner;
+}