From 487fe83dcad098310fcb15d5cea72630c74e8aae Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sat, 26 Aug 2017 17:54:54 -0400
Subject: [PATCH] Ensures that vertical sync and end-of-visible-lines
 conditions potentially trigger whenever line_counter_ changes, not only when
 it increments.

---
 Components/6845/CRTC6845.hpp | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/Components/6845/CRTC6845.hpp b/Components/6845/CRTC6845.hpp
index fea89eeb1..88c3f81c6 100644
--- a/Components/6845/CRTC6845.hpp
+++ b/Components/6845/CRTC6845.hpp
@@ -75,8 +75,9 @@ template <class T> class CRTC6845 {
 				0xff, 0x1f, 0x7f, 0x1f, 0x3f, 0xff, 0x3f, 0xff
 			};
 
-			if(selected_register_ < 16)
+			if(selected_register_ < 16) {
 				registers_[selected_register_] = value & masks[selected_register_];
+			}
 		}
 
 		void trigger_light_pen() {
@@ -170,21 +171,21 @@ template <class T> class CRTC6845 {
 						}
 					} else {
 						line_counter_ = (line_counter_ + 1) & 0x7f;
-
-						// check for start of vertical sync
-						if(line_counter_ == registers_[7]) {
-							bus_state_.vsync = true;
-							vsync_counter_ = 0;
-						}
-
-						// check for end of visible lines
-						if(line_counter_ == registers_[6]) {
-							line_is_visible_ = false;
-						}
 					}
 				} else {
 					bus_state_.row_address = (bus_state_.row_address + 1) & 0x1f;
 				}
+
+				// check for start of vertical sync
+				if(line_counter_ == registers_[7]) {
+					bus_state_.vsync = true;
+					vsync_counter_ = 0;
+				}
+
+				// check for end of visible lines
+				if(line_counter_ == registers_[6]) {
+					line_is_visible_ = false;
+				}
 			}
 
 			bus_state_.refresh_address = line_address_;