From 22cab0210be4e777756ddca6a0f79b8ac6c8a0ca Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Wed, 12 Jan 2022 06:26:10 -0400
Subject: [PATCH] fix(cpu): make LDRH and STRH aware of r15

---
 src/cpu/half_signed_data_transfer.zig | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/cpu/half_signed_data_transfer.zig b/src/cpu/half_signed_data_transfer.zig
index 7ad507b..b46565f 100644
--- a/src/cpu/half_signed_data_transfer.zig
+++ b/src/cpu/half_signed_data_transfer.zig
@@ -13,7 +13,13 @@ pub fn halfAndSignedDataTransfer(comptime P: bool, comptime U: bool, comptime I:
             const rm = opcode & 0xF;
             const imm_offset_high = opcode >> 8 & 0xF;
 
-            const base = cpu.r[rn];
+            var base: u32 = undefined;
+            if (rn == 0xF) {
+                base = cpu.fakePC();
+                if (!L) base += 4;
+            } else {
+                base = cpu.r[rn];
+            }
 
             var offset: u32 = undefined;
             if (I) {
@@ -33,7 +39,8 @@ pub fn halfAndSignedDataTransfer(comptime P: bool, comptime U: bool, comptime I:
                     },
                     0b01 => {
                         // LDRH
-                        cpu.r[rd] = bus.read16(address);
+                        const value = bus.read16(address & 0xFFFE);
+                        cpu.r[rd] = std.math.rotr(u32, @as(u32, value), 8 * (address & 1));
                     },
                     0b10 => {
                         // LDRSB