Interrupt system implemented, some new programs.

Source/Emulator/io.h

@@ -13,4 +13,20 @@ uint8_t OutputHandler(uint8_t DataByte, uint8_t Address);
 
 uint8_t InputHandler(uint8_t Address);
 
+// ---- Interrupt lines ----
+//
+// One line per port. A device puts its line up to ask for attention, and the CPU takes
+// it down when it answers. Which line a device uses is not a choice: a device on port N
+// interrupts on N, which is what saves the machine from needing any arbitration.
+//
+// These belong to the bus rather than to the CPU. Nothing here is saved in a frame, and
+// a program cannot read them except by being interrupted.
+
+void raiseInterrupt(uint8_t port);
+
+void clearInterrupt(uint8_t port);
+
+// The lowest numbered port with its line up, or -1 if none of them are.
+int nextPendingInterrupt(void);
+
 #endif // IO_H