// license:BSD-3-Clause
// copyright-holders:Aaron Giles
/***************************************************************************

  RIOT 6532 emulation

The timer seems to follow these rules:
- When the timer flag changes from 0 to 1 the timer continues to count
  down at a 1 cycle rate.
- When the timer is being read or written the timer flag is reset.
- When the timer flag is set and the timer contents are 0, the counting
  stops.

***************************************************************************/

#include "emu.h"
#include "6532riot.h"


//**************************************************************************
//  CONSTANTS
//**************************************************************************

// device type definition
const device_type RIOT6532 = &device_creator<riot6532_device>;

enum
{
	TIMER_IDLE,
	TIMER_COUNTING,
	TIMER_FINISHING
};

#define TIMER_FLAG      0x80
#define PA7_FLAG        0x40



/***************************************************************************
    INTERNAL FUNCTIONS
***************************************************************************/

/*-------------------------------------------------
    update_irqstate - update the IRQ state
    based on interrupt enables
-------------------------------------------------*/

void riot6532_device::update_irqstate()
{
	int irq = (m_irqstate & m_irqenable) ? ASSERT_LINE : CLEAR_LINE;

	if (m_irq != irq)
	{
		m_irq_cb(irq);
		m_irq = irq;
	}
}


/*-------------------------------------------------
    apply_ddr - combine inputs and outputs
    according to the DDR
-------------------------------------------------*/

UINT8 riot6532_device::apply_ddr(const riot6532_port *port)
{
	return (port->m_out & port->m_ddr) | (port->m_in & ~port->m_ddr);
}


/*-------------------------------------------------
    update_pa7_state - see if PA7 has changed
    and signal appropriately
-------------------------------------------------*/

void riot6532_device::update_pa7_state()
{
	UINT8 data = apply_ddr(&m_port[0]) & 0x80;

	/* if the state changed in the correct direction, set the PA7 flag and update IRQs */
	if ((m_pa7prev ^ data) && (m_pa7dir ^ data) == 0)
	{
		m_irqstate |= PA7_FLAG;
		update_irqstate();
	}
	m_pa7prev = data;
}


/*-------------------------------------------------
    get_timer - return the current timer value
-------------------------------------------------*/

UINT8 riot6532_device::get_timer()
{
	/* if idle, return 0 */
	if (m_timerstate == TIMER_IDLE)
	{
		return 0;
	}

	/* if counting, return the number of ticks remaining */
	else if (m_timerstate == TIMER_COUNTING)
	{
		return m_timer->remaining().as_ticks(clock()) >> m_timershift;
	}

	/* if finishing, return the number of ticks without the shift */
	else
	{
		return m_timer->remaining().as_ticks(clock());
	}
}



void riot6532_device::timer_end()
{
	assert(m_timerstate != TIMER_IDLE);

	/* if we finished counting, switch to the finishing state */
	if(m_timerstate == TIMER_COUNTING)
	{
		m_timerstate = TIMER_FINISHING;
		m_timer->adjust(attotime::from_ticks(256, clock()));

		/* signal timer IRQ as well */
		m_irqstate |= TIMER_FLAG;
		update_irqstate();
	}

	/* if we finished finishing, keep spinning */
	else if (m_timerstate == TIMER_FINISHING)
	{
		m_timer->adjust(attotime::from_ticks(256, clock()));
	}
}



/***************************************************************************
    I/O ACCESS
***************************************************************************/

/*-------------------------------------------------
    riot6532_w - master I/O write access
-------------------------------------------------*/

WRITE8_MEMBER( riot6532_device::write )
{
	reg_w(offset, data);
}

void riot6532_device::reg_w(UINT8 offset, UINT8 data)
{
	/* if A4 == 1 and A2 == 1, we are writing to the timer */
	if ((offset & 0x14) == 0x14)
	{
		static const UINT8 timershift[4] = { 0, 3, 6, 10 };
		attotime curtime = machine().time();
		INT64 target;

		/* A0-A1 contain the timer divisor */
		m_timershift = timershift[offset & 3];

		/* A3 contains the timer IRQ enable */
		if (offset & 8)
			m_irqenable |= TIMER_FLAG;
		else
			m_irqenable &= ~TIMER_FLAG;

		/* writes here clear the timer flag */
		if (m_timerstate != TIMER_FINISHING || get_timer() != 0xff)
		{
			m_irqstate &= ~TIMER_FLAG;
		}
		update_irqstate();

		/* update the timer */
		m_timerstate = TIMER_COUNTING;
		target = curtime.as_ticks(clock()) + 1 + (data << m_timershift);
		m_timer->adjust(attotime::from_ticks(target, clock()) - curtime);
	}

	/* if A4 == 0 and A2 == 1, we are writing to the edge detect control */
	else if ((offset & 0x14) == 0x04)
	{
		/* A1 contains the A7 IRQ enable */
		if (offset & 2)
		{
			m_irqenable |= PA7_FLAG;
		}
		else
		{
			m_irqenable &= ~PA7_FLAG;
		}

		/* A0 specifies the edge detect direction: 0=negative, 1=positive */
		m_pa7dir = (offset & 1) << 7;
	}

	/* if A4 == anything and A2 == 0, we are writing to the I/O section */
	else
	{
		/* A1 selects the port */
		riot6532_port *port = &m_port[BIT(offset, 1)];

		/* if A0 == 1, we are writing to the port's DDR */
		if (offset & 1)
		{
			port->m_ddr = data;
		}

		/* if A0 == 0, we are writing to the port's output */
		else
		{
			port->m_out = data;
			(*port->m_out_cb)((offs_t)0, data);
		}

		/* writes to port A need to update the PA7 state */
		if (port == &m_port[0])
		{
			update_pa7_state();
		}
	}
}


/*-------------------------------------------------
    riot6532_r - master I/O read access
-------------------------------------------------*/

READ8_MEMBER( riot6532_device::read )
{
	return reg_r(offset, space.debugger_access());
}

UINT8 riot6532_device::reg_r(UINT8 offset, bool debugger_access)
{
	UINT8 val;

	/* if A2 == 1 and A0 == 1, we are reading interrupt flags */
	if ((offset & 0x05) == 0x05)
	{
		val = m_irqstate;

		if ( ! debugger_access )
		{
			/* implicitly clears the PA7 flag */
			m_irqstate &= ~PA7_FLAG;
			update_irqstate();
		}
	}

	/* if A2 == 1 and A0 == 0, we are reading the timer */
	else if ((offset & 0x05) == 0x04)
	{
		val = get_timer();

		if ( ! debugger_access )
		{
			/* A3 contains the timer IRQ enable */
			if (offset & 8)
			{
				m_irqenable |= TIMER_FLAG;
			}
			else
			{
				m_irqenable &= ~TIMER_FLAG;
			}

			/* implicitly clears the timer flag */
			if (m_timerstate != TIMER_FINISHING || val != 0xff)
			{
				m_irqstate &= ~TIMER_FLAG;
			}
			update_irqstate();
		}
	}

	/* if A2 == 0 and A0 == anything, we are reading from ports */
	else
	{
		/* A1 selects the port */
		riot6532_port *port = &m_port[BIT(offset, 1)];

		/* if A0 == 1, we are reading the port's DDR */
		if (offset & 1)
		{
			val = port->m_ddr;
		}

		/* if A0 == 0, we are reading the port as an input */
		else
		{
			/* call the input callback if it exists */
			if (!(*port->m_in_cb).isnull())
			{
				port->m_in = (*port->m_in_cb)(0);

				/* changes to port A need to update the PA7 state */
				if (port == &m_port[0])
				{
					if (!debugger_access)
					{
						update_pa7_state();
					}
				}
			}

			/* apply the DDR to the result */
			val = apply_ddr(port);
		}
	}
	return val;
}


/*-------------------------------------------------
    porta_in_set - set port A input value
-------------------------------------------------*/

void riot6532_device::porta_in_set(UINT8 data, UINT8 mask)
{
	m_port[0].m_in = (m_port[0].m_in & ~mask) | (data & mask);
	update_pa7_state();
}


/*-------------------------------------------------
    portb_in_set - set port B input value
-------------------------------------------------*/

void riot6532_device::portb_in_set(UINT8 data, UINT8 mask)
{
	m_port[1].m_in = (m_port[1].m_in & ~mask) | (data & mask);
}


/*-------------------------------------------------
    porta_in_get - return port A input value
-------------------------------------------------*/

UINT8 riot6532_device::porta_in_get()
{
	return m_port[0].m_in;
}


/*-------------------------------------------------
    portb_in_get - return port B input value
-------------------------------------------------*/

UINT8 riot6532_device::portb_in_get()
{
	return m_port[1].m_in;
}


/*-------------------------------------------------
    porta_in_get - return port A output value
-------------------------------------------------*/

UINT8 riot6532_device::porta_out_get()
{
	return m_port[0].m_out;
}


/*-------------------------------------------------
    portb_in_get - return port B output value
-------------------------------------------------*/

UINT8 riot6532_device::portb_out_get()
{
	return m_port[1].m_out;
}


//**************************************************************************
//  LIVE DEVICE
//**************************************************************************

//-------------------------------------------------
//  riot6532_device - constructor
//-------------------------------------------------

riot6532_device::riot6532_device(const machine_config &mconfig, const char *tag, device_t *owner, UINT32 clock)
	: device_t(mconfig, RIOT6532, "6532 RIOT", tag, owner, clock, "riot6532", __FILE__),
		m_in_pa_cb(*this),
		m_out_pa_cb(*this),
		m_in_pb_cb(*this),
		m_out_pb_cb(*this),
		m_irq_cb(*this),
		m_irqstate(0),
		m_irqenable(0),
		m_irq(CLEAR_LINE),
		m_pa7dir(0),
		m_pa7prev(0),
		m_timershift(0),
		m_timerstate(0),
		m_timer(nullptr)
{
	memset(m_port, 0x00, sizeof(m_port));
}

/*-------------------------------------------------
    device_start - device-specific startup
-------------------------------------------------*/

void riot6532_device::device_start()
{
	/* resolve callbacks */
	m_in_pa_cb.resolve();
	m_port[0].m_in_cb = &m_in_pa_cb;
	m_out_pa_cb.resolve_safe();
	m_port[0].m_out_cb = &m_out_pa_cb;
	m_in_pb_cb.resolve();
	m_port[1].m_in_cb = &m_in_pb_cb;
	m_out_pb_cb.resolve_safe();
	m_port[1].m_out_cb = &m_out_pb_cb;
	m_irq_cb.resolve_safe();

	/* allocate timers */
	m_timer = timer_alloc(TIMER_END_CB);

	/* register for save states */
	save_item(NAME(m_port[0].m_in));
	save_item(NAME(m_port[0].m_out));
	save_item(NAME(m_port[0].m_ddr));
	save_item(NAME(m_port[1].m_in));
	save_item(NAME(m_port[1].m_out));
	save_item(NAME(m_port[1].m_ddr));

	save_item(NAME(m_irqstate));
	save_item(NAME(m_irqenable));
	save_item(NAME(m_irq));

	save_item(NAME(m_pa7dir));
	save_item(NAME(m_pa7prev));

	save_item(NAME(m_timershift));
	save_item(NAME(m_timerstate));
}



/*-------------------------------------------------
    device_reset - device-specific reset
-------------------------------------------------*/

void riot6532_device::device_reset()
{
	/* reset I/O states */
	m_port[0].m_in = 0;
	m_port[0].m_out = 0;
	m_port[0].m_ddr = 0;
	m_port[1].m_in = 0;
	m_port[1].m_out = 0;
	m_port[1].m_ddr = 0;

	/* reset IRQ states */
	m_irqenable = 0;
	m_irqstate = 0;
	update_irqstate();

	/* reset PA7 states */
	m_pa7dir = 0;
	m_pa7prev = 0;

	/* reset timer states */
	m_timershift = 10;
	m_timerstate = TIMER_COUNTING;
	m_timer->adjust(attotime::from_ticks(256 << m_timershift, clock()));
}

void riot6532_device::device_timer(emu_timer &timer, device_timer_id id, int param, void *ptr)
{
	switch (id)
	{
		case TIMER_END_CB:
			timer_end();
			break;
		default:
			assert_always(FALSE, "Unknown id in riot6532_device::device_timer");
	}
}
