Force drive selection; verify that the index hole is going by.

Machines/Thomson/MO5/CD90-640.cpp

@@ -36,8 +36,9 @@ void CD90_640::set_activity_observer(Activity::Observer *const observer) {
 void CD90_640::set_disk(std::shared_ptr<Storage::Disk::Disk> disk, const size_t drive) {
 	get_drive(drive).set_disk(disk);
 
-	// TODO: what is really in charge of motor control?
+	// TODO: what is really in charge of motor control and drive selection?
 	get_drive(drive).set_motor_on(true);
+	set_drive(1 << drive);
 }
 
 const Storage::Disk::Disk *CD90_640::disk(const std::string &name) {

Machines/Thomson/MO5/CD90-640.hpp

@@ -25,12 +25,15 @@ public:
 
 	template <int address>
 	uint8_t read() {
-		Logger::info().append("Read %04x", address);
-		if(address & 8) {
-			return control();
-		} else {
-			return WD::WD1770::read(address);
-		}
+		const uint8_t result = [&] {
+			if(address & 8) {
+				return control();
+			} else {
+				return WD::WD1770::read(address);
+			}
+		} ();
+		Logger::info().append("Read %02x <- %04x", result, address);
+		return result;
 	}
 
 	template <int address>