From 337ca2cfaf4c5dee0ce8c2de86bfb29507040735 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Sun, 5 Sep 2021 12:20:46 -0700
Subject: [PATCH] GB I/O: Fix incrementing SGB controller when P14 is low
 (fixes #2202)

---
 CHANGES     |  1 +
 src/gb/io.c | 14 +++++---------
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/CHANGES b/CHANGES
index 0356ef0c8..a90532f6c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -10,6 +10,7 @@ Features:
  - Discord Rich Presence now supports time elapsed
  - Additional scaling shaders
 Emulation fixes:
+ - GB I/O: Fix incrementing SGB controller when P14 is low (fixes mgba.io/i/2202)
  - GB Memory: Add cursory cartridge open bus emulation (fixes mgba.io/i/2032)
  - GB Video: Render SGB border when unmasking with ATTR/PAL_SET (fixes mgba.io/i/2261)
  - GBA: Improve timing when not booting from BIOS
diff --git a/src/gb/io.c b/src/gb/io.c
index 00f75ffd7..74ce4caee 100644
--- a/src/gb/io.c
+++ b/src/gb/io.c
@@ -119,19 +119,15 @@ static void _writeSGBBits(struct GB* gb, int bits) {
 	if (bits == gb->currentSgbBits) {
 		return;
 	}
-	switch (bits) {
-	case 0:
-	case 1:
-		if (gb->currentSgbBits & 2) {
-			gb->sgbIncrement = !gb->sgbIncrement;
-		}
-		break;
-	case 3:
+	if (bits & 2) {
 		if (gb->sgbIncrement) {
 			gb->sgbIncrement = false;
 			gb->sgbCurrentController = (gb->sgbCurrentController + 1) & gb->sgbControllers;
 		}
-		break;
+	} else {
+		if (gb->currentSgbBits & 2) {
+			gb->sgbIncrement = !gb->sgbIncrement;
+		}
 	}
 	gb->currentSgbBits = bits;
 	if (gb->sgbBit == 128 && bits == 2) {