From 6575eb5531aa749e1143fe4f7b0ae06c73bf91c7 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Wed, 5 May 2021 19:23:01 -0500
Subject: [PATCH] chore(bus): ensure no read-only bits are overwritten by the
 cpu

---
 src/joypad.rs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/joypad.rs b/src/joypad.rs
index f926172..b6fea58 100644
--- a/src/joypad.rs
+++ b/src/joypad.rs
@@ -29,11 +29,11 @@ bitfield! {
 
 impl JoypadStatus {
     pub(crate) fn update(&mut self, byte: u8) {
-        let action_row = (byte >> 5) & 0x01;
-        let direction_row = (byte >> 4) & 0x01;
+        // Bytes 3 -> 0 are Read Only
+        let mask = 0b00001111;
 
-        self.set_action_row(action_row.into());
-        self.set_direction_row(direction_row.into());
+        let read_only = self.0 & mask;
+        self.0 = (byte & !mask) | read_only;
     }
 }