From cfbd292edc0b8da74c29315a1171369e1f73f807 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Sat, 29 Jan 2022 01:17:11 -0400
Subject: [PATCH] feat(cpu): implement format 6 THUMB instructions

---
 src/cpu.zig               |  7 +++++++
 src/cpu/thumb/format6.zig | 16 ++++++++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 src/cpu/thumb/format6.zig

diff --git a/src/cpu.zig b/src/cpu.zig
index 6292cde..284647f 100644
--- a/src/cpu.zig
+++ b/src/cpu.zig
@@ -22,6 +22,7 @@ const softwareInterrupt = @import("cpu/arm/software_interrupt.zig").softwareInte
 // THUMB Instruction Groups
 const format3 = @import("cpu/thumb/format3.zig").format3;
 const format5 = @import("cpu/thumb/format5.zig").format5;
+const format6 = @import("cpu/thumb/format6.zig").format6;
 const format12 = @import("cpu/thumb/format12.zig").format12;
 
 pub const ArmInstrFn = fn (*Arm7tdmi, *Bus, u32) void;
@@ -330,6 +331,12 @@ fn thumbPopulate() [0x400]ThumbInstrFn {
                 lut[i] = format5(op, h1, h2);
             }
 
+            if (i >> 5 & 0x1F == 0b01001) {
+                const rd = i >> 2 & 0x7;
+
+                lut[i] = format6(rd);
+            }
+
             if (i >> 6 & 0xF == 0b1010) {
                 const isSP = i >> 5 & 1 == 1;
                 const rd = i >> 2 & 0x7;
diff --git a/src/cpu/thumb/format6.zig b/src/cpu/thumb/format6.zig
new file mode 100644
index 0000000..e90be49
--- /dev/null
+++ b/src/cpu/thumb/format6.zig
@@ -0,0 +1,16 @@
+const std = @import("std");
+
+const Bus = @import("../../Bus.zig");
+const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
+const InstrFn = @import("../../cpu.zig").ThumbInstrFn;
+
+pub fn format6(comptime rd: u3) InstrFn {
+    return struct {
+        fn inner(cpu: *Arm7tdmi, bus: *Bus, opcode: u16) void {
+            const offset = (opcode & 0xFF) << 2;
+
+            // FIXME: Should this overflow?
+            cpu.r[rd] = bus.read32((cpu.fakePC() & 0xFFFF_FFFC) + offset);
+        }
+    }.inner;
+}