// io.h
// I/O for the SplitBit CPU Emulator
// Written by Anachronaut
// 10/16/2024

#ifndef IO_H
#define IO_H

#include <stdint.h>
#include "cpu.h"

// ---- Ports ----
//
// Which port a device answers on is a property of the machine rather than of any
// program, so the numbers live here and everything else refers to them by name.

#define PORT_CONSOLE  0x00
#define PORT_TEST     0x10
#define PORT_REFUSE   0x11
#define PORT_MEMORY   0x12
#define PORT_REGISTRY 0xFF

// ---- Device classes ----
//
// What kind of thing is plugged into a port. Class 0 is not a device: reading an
// unimplemented port already gives zero, so "nothing there" needs no special case and a
// machine with no registry at all answers correctly by doing nothing.
//
// Classes 0x01 to 0x0F belong to the machine itself. Peripherals start at 0x10.

#define DEVICE_NONE     0x00
#define DEVICE_REGISTRY 0x01
#define DEVICE_CONSOLE  0x02
#define DEVICE_CONTROLLER 0x03
#define DEVICE_TEST     0x10
#define DEVICE_REFUSE   0x11
#define DEVICE_MEMORY   0x12

// What a device brings besides itself. This means memory that somebody has to register
// with the controller, so the controller's own bank 2 does not count: it is already there.
#define DEVICE_FLAG_HAS_MEMORY 0x01

// How many bytes a device's entry in the registry runs to. Reading past the end gives
// zero, so the record can grow later without anything already written having to change.
#define DEVICE_RECORD_BYTES 2

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);

// ---- Refusing ----
//
// A device can refuse what it was asked to do. Interrupting is a device asking for
// attention later; refusing is a device saying no to the instruction happening now, so
// it has to stop the machine where it stands rather than raise a line and let execution
// carry on past the mistake.
//
// The refusal names a software vector, so the cause is known from the entry it arrives
// through, the same way every other fault on this machine works.

void refuseAccess(uint8_t faultVector);

// ---- Memory a device brings ----
//
// Returns the memory owned by the device on this port, or NULL if it owns none, and
// fills in how much of it there is. This is how the controller finds out what a device
// brings when it is told to register a bank.
//
// It is a direct look at the machine's device table rather than a conversation through
// the registry's port. The port protocol remembers which port it was asked about, so a
// controller that used it would silently lose the place of any enumeration a program had
// in progress. Same table, two consumers, and only one of them needs the protocol.
uint8_t *deviceMemory(uint8_t port, uint32_t *capacity);

// The vector a device refused with, or 0 if none did. Reading it clears it, because a
// refusal is answered once.
uint8_t takeRefusal(void);

// Which port did the refusing. Only meaningful alongside a refusal.
uint8_t refusingPort(void);

#endif // IO_H