From 5a59c31b72a63c52508d33f01f41791e80852e11 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Mon, 3 May 2021 23:37:30 -0500
Subject: [PATCH] fix(joypad): fix bug where gameboy overwrites read only bits

---
 src/bus.rs    |  2 +-
 src/joypad.rs | 16 ++++++++++------
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/src/bus.rs b/src/bus.rs
index 61fe178..a8050d6 100644
--- a/src/bus.rs
+++ b/src/bus.rs
@@ -243,7 +243,7 @@ impl Bus {
             0xFF00..=0xFF7F => {
                 // IO Registers
                 match addr {
-                    0xFF00 => self.joypad.status = byte.into(),
+                    0xFF00 => self.joypad.status.update(byte),
                     0xFF01 => self.serial.next = byte,
                     0xFF02 => self.serial.control = byte.into(),
                     0xFF04 => self.timer.divider = 0x00,
diff --git a/src/joypad.rs b/src/joypad.rs
index 73a7639..f926172 100644
--- a/src/joypad.rs
+++ b/src/joypad.rs
@@ -27,6 +27,16 @@ bitfield! {
     from into ButtonState, right_a, _set_right_a: 0, 0;
 }
 
+impl JoypadStatus {
+    pub(crate) fn update(&mut self, byte: u8) {
+        let action_row = (byte >> 5) & 0x01;
+        let direction_row = (byte >> 4) & 0x01;
+
+        self.set_action_row(action_row.into());
+        self.set_direction_row(direction_row.into());
+    }
+}
+
 impl JoypadStatus {
     pub fn set_down_start(&mut self, state: ButtonState, int: &mut bool) {
         if !(*int) {
@@ -74,12 +84,6 @@ impl Clone for JoypadStatus {
     }
 }
 
-impl From<u8> for JoypadStatus {
-    fn from(byte: u8) -> Self {
-        Self(byte)
-    }
-}
-
 impl From<JoypadStatus> for u8 {
     fn from(status: JoypadStatus) -> Self {
         status.0