From 4fca30b81f2e4b0133b2f7d9691aa7cca28f258f Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sun, 25 Dec 2016 21:06:58 -0500
Subject: [PATCH] Made the Plus 3 less chatty, documented `invalidate_track`.

---
 Machines/Electron/Plus3.cpp     | 26 ++++++++++++++++++--------
 Machines/Electron/Plus3.hpp     |  1 +
 Storage/Disk/DiskController.hpp |  4 ++++
 3 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/Machines/Electron/Plus3.cpp b/Machines/Electron/Plus3.cpp
index 52035dd3d..9100a860c 100644
--- a/Machines/Electron/Plus3.cpp
+++ b/Machines/Electron/Plus3.cpp
@@ -24,18 +24,28 @@ void Plus3::set_disk(std::shared_ptr<Storage::Disk::Disk> disk, int drive)
 
 void Plus3::set_control_register(uint8_t control)
 {
-	// TODO:
 	//	bit 0 => enable or disable drive 1
 	//	bit 1 => enable or disable drive 2
 	//	bit 2 => side select
 	//	bit 3 => single density select
-	switch(control&3)
+
+	uint8_t changes = control ^ last_control_;
+	last_control_ = control;
+
+	if(changes&3)
 	{
-		case 0:		selected_drive_ = -1;	set_drive(nullptr);		break;
-		default:	selected_drive_ = 0;	set_drive(drives_[0]);	break;
-		case 2:		selected_drive_ = 1;	set_drive(drives_[1]);	break;
+		switch(control&3)
+		{
+			case 0:		selected_drive_ = -1;	set_drive(nullptr);		break;
+			default:	selected_drive_ = 0;	set_drive(drives_[0]);	break;
+			case 2:		selected_drive_ = 1;	set_drive(drives_[1]);	break;
+		}
 	}
-	if(drives_[0]) drives_[0]->set_head((control & 0x04) ? 1 : 0);
-	if(drives_[1]) drives_[1]->set_head((control & 0x04) ? 1 : 0);
-	set_is_double_density(!(control & 0x08));
+	if(changes & 0x04)
+	{
+		invalidate_track();
+		if(drives_[0]) drives_[0]->set_head((control & 0x04) ? 1 : 0);
+		if(drives_[1]) drives_[1]->set_head((control & 0x04) ? 1 : 0);
+	}
+	if(changes & 0x08) set_is_double_density(!(control & 0x08));
 }
diff --git a/Machines/Electron/Plus3.hpp b/Machines/Electron/Plus3.hpp
index cd04b3877..8e6b7c0e4 100644
--- a/Machines/Electron/Plus3.hpp
+++ b/Machines/Electron/Plus3.hpp
@@ -23,6 +23,7 @@ class Plus3 : public WD::WD1770 {
 	private:
 		std::shared_ptr<Storage::Disk::Drive> drives_[2];
 		int selected_drive_;
+		uint8_t last_control_;
 };
 
 }
diff --git a/Storage/Disk/DiskController.hpp b/Storage/Disk/DiskController.hpp
index f309307bc..a39b74b48 100644
--- a/Storage/Disk/DiskController.hpp
+++ b/Storage/Disk/DiskController.hpp
@@ -49,6 +49,10 @@ class Controller: public DigitalPhaseLockedLoop::Delegate, public TimedEventLoop
 			Sets the current drive.
 		*/
 		void set_drive(std::shared_ptr<Drive> drive);
+
+		/*!
+			Announces that the track the drive sees is about to change for a reason unknownt to the controller.
+		*/
 		void invalidate_track();
 
 		/*!