serial.c

/*
 * QEMU 16550A UART emulation
 *
 * Copyright (c) 2003-2004 Fabrice Bellard
 * Copyright (c) 2008 Citrix Systems, Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "hw/char/serial.h"
#include "sysemu/char.h"
#include "qemu/timer.h"
#include "exec/address-spaces.h"

//#define DEBUG_SERIAL

#define UART_LCR_DLAB	0x80	/* Divisor latch access bit */

#define UART_IER_MSI	0x08	/* Enable Modem status interrupt */
#define UART_IER_RLSI	0x04	/* Enable receiver line status interrupt */
#define UART_IER_THRI	0x02	/* Enable Transmitter holding register int. */
#define UART_IER_RDI	0x01	/* Enable receiver data interrupt */

#define UART_IIR_NO_INT	0x01	/* No interrupts pending */
#define UART_IIR_ID	0x06	/* Mask for the interrupt ID */

#define UART_IIR_MSI	0x00	/* Modem status interrupt */
#define UART_IIR_THRI	0x02	/* Transmitter holding register empty */
#define UART_IIR_RDI	0x04	/* Receiver data interrupt */
#define UART_IIR_RLSI	0x06	/* Receiver line status interrupt */
#define UART_IIR_CTI    0x0C    /* Character Timeout Indication */

#define UART_IIR_FENF   0x80    /* Fifo enabled, but not functionning */
#define UART_IIR_FE     0xC0    /* Fifo enabled */

/*
 * These are the definitions for the Modem Control Register
 */
#define UART_MCR_LOOP	0x10	/* Enable loopback test mode */
#define UART_MCR_OUT2	0x08	/* Out2 complement */
#define UART_MCR_OUT1	0x04	/* Out1 complement */
#define UART_MCR_RTS	0x02	/* RTS complement */
#define UART_MCR_DTR	0x01	/* DTR complement */

/*
 * These are the definitions for the Modem Status Register
 */
#define UART_MSR_DCD	0x80	/* Data Carrier Detect */
#define UART_MSR_RI	0x40	/* Ring Indicator */
#define UART_MSR_DSR	0x20	/* Data Set Ready */
#define UART_MSR_CTS	0x10	/* Clear to Send */
#define UART_MSR_DDCD	0x08	/* Delta DCD */
#define UART_MSR_TERI	0x04	/* Trailing edge ring indicator */
#define UART_MSR_DDSR	0x02	/* Delta DSR */
#define UART_MSR_DCTS	0x01	/* Delta CTS */
#define UART_MSR_ANY_DELTA 0x0F	/* Any of the delta bits! */

#define UART_LSR_TEMT	0x40	/* Transmitter empty */
#define UART_LSR_THRE	0x20	/* Transmit-hold-register empty */
#define UART_LSR_BI	0x10	/* Break interrupt indicator */
#define UART_LSR_FE	0x08	/* Frame error indicator */
#define UART_LSR_PE	0x04	/* Parity error indicator */
#define UART_LSR_OE	0x02	/* Overrun error indicator */
#define UART_LSR_DR	0x01	/* Receiver data ready */
#define UART_LSR_INT_ANY 0x1E	/* Any of the lsr-interrupt-triggering status bits */

/* Interrupt trigger levels. The byte-counts are for 16550A - in newer UARTs the byte-count for each ITL is higher. */

#define UART_FCR_ITL_1      0x00 /* 1 byte ITL */
#define UART_FCR_ITL_2      0x40 /* 4 bytes ITL */
#define UART_FCR_ITL_3      0x80 /* 8 bytes ITL */
#define UART_FCR_ITL_4      0xC0 /* 14 bytes ITL */

#define UART_FCR_DMS        0x08    /* DMA Mode Select */
#define UART_FCR_XFR        0x04    /* XMIT Fifo Reset */
#define UART_FCR_RFR        0x02    /* RCVR Fifo Reset */
#define UART_FCR_FE         0x01    /* FIFO Enable */

#define XMIT_FIFO           0
#define RECV_FIFO           1
#define MAX_XMIT_RETRY      4

#ifdef DEBUG_SERIAL
#define DPRINTF(fmt, ...) \
do { fprintf(stderr, "serial: " fmt , ## __VA_ARGS__); } while (0)
#else
#define DPRINTF(fmt, ...) \
do {} while (0)
#endif

static void serial_receive1(void *opaque, const uint8_t *buf, int size);

static void fifo_clear(SerialState *s, int fifo)
{
    SerialFIFO *f = (fifo) ? &s->recv_fifo : &s->xmit_fifo;
    memset(f->data, 0, UART_FIFO_LENGTH);
    f->count = 0;
    f->head = 0;
    f->tail = 0;
}

static int fifo_put(SerialState *s, int fifo, uint8_t chr)
{
    SerialFIFO *f = (fifo) ? &s->recv_fifo : &s->xmit_fifo;

    /* Receive overruns do not overwrite FIFO contents. */
    if (fifo == XMIT_FIFO || f->count < UART_FIFO_LENGTH) {

        f->data[f->head++] = chr;

        if (f->head == UART_FIFO_LENGTH)
            f->head = 0;
    }

    if (f->count < UART_FIFO_LENGTH)
        f->count++;
    else if (fifo == RECV_FIFO)
        s->lsr |= UART_LSR_OE;

    return 1;
}

static uint8_t fifo_get(SerialState *s, int fifo)
{
    SerialFIFO *f = (fifo) ? &s->recv_fifo : &s->xmit_fifo;
    uint8_t c;

    if(f->count == 0)
        return 0;

    c = f->data[f->tail++];
    if (f->tail == UART_FIFO_LENGTH)
        f->tail = 0;
    f->count--;

    return c;
}

static void serial_update_irq(SerialState *s)
{
    uint8_t tmp_iir = UART_IIR_NO_INT;

    if ((s->ier & UART_IER_RLSI) && (s->lsr & UART_LSR_INT_ANY)) {
        tmp_iir = UART_IIR_RLSI;
    } else if ((s->ier & UART_IER_RDI) && s->timeout_ipending) {
        /* Note that(s->ier & UART_IER_RDI) can mask this interrupt,
         * this is not in the specification but is observed on existing
         * hardware.  */
        tmp_iir = UART_IIR_CTI;
    } else if ((s->ier & UART_IER_RDI) && (s->lsr & UART_LSR_DR) &&
               (!(s->fcr & UART_FCR_FE) ||
                s->recv_fifo.count >= s->recv_fifo.itl)) {
        tmp_iir = UART_IIR_RDI;
    } else if ((s->ier & UART_IER_THRI) && s->thr_ipending) {
        tmp_iir = UART_IIR_THRI;
    } else if ((s->ier & UART_IER_MSI) && (s->msr & UART_MSR_ANY_DELTA)) {
        tmp_iir = UART_IIR_MSI;
    }

    s->iir = tmp_iir | (s->iir & 0xF0);

    if (tmp_iir != UART_IIR_NO_INT) {
        qemu_irq_raise(s->irq);
    } else {
        qemu_irq_lower(s->irq);
    }
}

static void serial_update_parameters(SerialState *s)
{
    int speed, parity, data_bits, stop_bits, frame_size;
    QEMUSerialSetParams ssp;

    if (s->divider == 0)
        return;

    /* Start bit. */
    frame_size = 1;
    if (s->lcr & 0x08) {
        /* Parity bit. */
        frame_size++;
        if (s->lcr & 0x10)
            parity = 'E';
        else
            parity = 'O';
    } else {
            parity = 'N';
    }
    if (s->lcr & 0x04)
        stop_bits = 2;
    else
        stop_bits = 1;

    data_bits = (s->lcr & 0x03) + 5;
    frame_size += data_bits + stop_bits;
    speed = s->baudbase / s->divider;
    ssp.speed = speed;
    ssp.parity = parity;
    ssp.data_bits = data_bits;
    ssp.stop_bits = stop_bits;
    s->char_transmit_time =  (get_ticks_per_sec() / speed) * frame_size;
    qemu_chr_fe_ioctl(s->chr, CHR_IOCTL_SERIAL_SET_PARAMS, &ssp);

    DPRINTF("speed=%d parity=%c data=%d stop=%d\n",
           speed, parity, data_bits, stop_bits);
}

static void serial_update_msl(SerialState *s)
{
    uint8_t omsr;
    int flags;

    qemu_del_timer(s->modem_status_poll);

    if (qemu_chr_fe_ioctl(s->chr,CHR_IOCTL_SERIAL_GET_TIOCM, &flags) == -ENOTSUP) {
        s->poll_msl = -1;
        return;
    }

    omsr = s->msr;

    s->msr = (flags & CHR_TIOCM_CTS) ? s->msr | UART_MSR_CTS : s->msr & ~UART_MSR_CTS;
    s->msr = (flags & CHR_TIOCM_DSR) ? s->msr | UART_MSR_DSR : s->msr & ~UART_MSR_DSR;
    s->msr = (flags & CHR_TIOCM_CAR) ? s->msr | UART_MSR_DCD : s->msr & ~UART_MSR_DCD;
    s->msr = (flags & CHR_TIOCM_RI) ? s->msr | UART_MSR_RI : s->msr & ~UART_MSR_RI;

    if (s->msr != omsr) {
         /* Set delta bits */
         s->msr = s->msr | ((s->msr >> 4) ^ (omsr >> 4));
         /* UART_MSR_TERI only if change was from 1 -> 0 */
         if ((s->msr & UART_MSR_TERI) && !(omsr & UART_MSR_RI))
             s->msr &= ~UART_MSR_TERI;
         serial_update_irq(s);
    }

    /* The real 16550A apparently has a 250ns response latency to line status changes.
       We'll be lazy and poll only every 10ms, and only poll it at all if MSI interrupts are turned on */

    if (s->poll_msl)
        qemu_mod_timer(s->modem_status_poll, qemu_get_clock_ns(vm_clock) + get_ticks_per_sec() / 100);
}

static gboolean serial_xmit(GIOChannel *chan, GIOCondition cond, void *opaque)
{
    SerialState *s = opaque;

    if (s->tsr_retry <= 0) {
        if (s->fcr & UART_FCR_FE) {
            s->tsr = fifo_get(s,XMIT_FIFO);
            if (!s->xmit_fifo.count)
                s->lsr |= UART_LSR_THRE;
        } else if ((s->lsr & UART_LSR_THRE)) {
            return FALSE;
        } else {
            s->tsr = s->thr;
            s->lsr |= UART_LSR_THRE;
            s->lsr &= ~UART_LSR_TEMT;
        }
    }

    if (s->mcr & UART_MCR_LOOP) {
        /* in loopback mode, say that we just received a char */
        serial_receive1(s, &s->tsr, 1);
    } else if (qemu_chr_fe_write(s->chr, &s->tsr, 1) != 1) {
        if (s->tsr_retry >= 0 && s->tsr_retry < MAX_XMIT_RETRY &&
            qemu_chr_fe_add_watch(s->chr, G_IO_OUT, serial_xmit, s) > 0) {
            s->tsr_retry++;
            return FALSE;
        }
        s->tsr_retry = 0;
    } else {
        s->tsr_retry = 0;
    }

    s->last_xmit_ts = qemu_get_clock_ns(vm_clock);

    if (s->lsr & UART_LSR_THRE) {
        s->lsr |= UART_LSR_TEMT;
        s->thr_ipending = 1;
        serial_update_irq(s);
    }

    return FALSE;
}


static void serial_ioport_write(void *opaque, hwaddr addr, uint64_t val,
                                unsigned size)
{
    SerialState *s = opaque;

    addr &= 7;
    DPRINTF("write addr=0x%" HWADDR_PRIx " val=0x%" PRIx64 "\n", addr, val);
    switch(addr) {
    default:
    case 0:
        if (s->lcr & UART_LCR_DLAB) {
            s->divider = (s->divider & 0xff00) | val;
            serial_update_parameters(s);
        } else {
            s->thr = (uint8_t) val;
            if(s->fcr & UART_FCR_FE) {
                fifo_put(s, XMIT_FIFO, s->thr);
                s->thr_ipending = 0;
                s->lsr &= ~UART_LSR_TEMT;
                s->lsr &= ~UART_LSR_THRE;
                serial_update_irq(s);
            } else {
                s->thr_ipending = 0;
                s->lsr &= ~UART_LSR_THRE;
                serial_update_irq(s);
            }
            serial_xmit(NULL, G_IO_OUT, s);
        }
        break;
    case 1:
        if (s->lcr & UART_LCR_DLAB) {
            s->divider = (s->divider & 0x00ff) | (val << 8);
            serial_update_parameters(s);
        } else {
            s->ier = val & 0x0f;
            /* If the backend device is a real serial port, turn polling of the modem
               status lines on physical port on or off depending on UART_IER_MSI state */
            if (s->poll_msl >= 0) {
                if (s->ier & UART_IER_MSI) {
                     s->poll_msl = 1;
                     serial_update_msl(s);
                } else {
                     qemu_del_timer(s->modem_status_poll);
                     s->poll_msl = 0;
                }
            }
            if (s->lsr & UART_LSR_THRE) {
                s->thr_ipending = 1;
                serial_update_irq(s);
            }
        }
        break;
    case 2:
        val = val & 0xFF;

        if (s->fcr == val)
            break;

        /* Did the enable/disable flag change? If so, make sure FIFOs get flushed */
        if ((val ^ s->fcr) & UART_FCR_FE)
            val |= UART_FCR_XFR | UART_FCR_RFR;

        /* FIFO clear */

        if (val & UART_FCR_RFR) {
            qemu_del_timer(s->fifo_timeout_timer);
            s->timeout_ipending=0;
            fifo_clear(s,RECV_FIFO);
        }

        if (val & UART_FCR_XFR) {
            fifo_clear(s,XMIT_FIFO);
        }

        if (val & UART_FCR_FE) {
            s->iir |= UART_IIR_FE;
            /* Set RECV_FIFO trigger Level */
            switch (val & 0xC0) {
            case UART_FCR_ITL_1:
                s->recv_fifo.itl = 1;
                break;
            case UART_FCR_ITL_2:
                s->recv_fifo.itl = 4;
                break;
            case UART_FCR_ITL_3:
                s->recv_fifo.itl = 8;
                break;
            case UART_FCR_ITL_4:
                s->recv_fifo.itl = 14;
                break;
            }
        } else
            s->iir &= ~UART_IIR_FE;

        /* Set fcr - or at least the bits in it that are supposed to "stick" */
        s->fcr = val & 0xC9;
        serial_update_irq(s);
        break;
    case 3:
        {
            int break_enable;
            s->lcr = val;
            serial_update_parameters(s);
            break_enable = (val >> 6) & 1;
            if (break_enable != s->last_break_enable) {
                s->last_break_enable = break_enable;
                qemu_chr_fe_ioctl(s->chr, CHR_IOCTL_SERIAL_SET_BREAK,
                               &break_enable);
            }
        }
        break;
    case 4:
        {
            int flags;
            int old_mcr = s->mcr;
            s->mcr = val & 0x1f;
            if (val & UART_MCR_LOOP)
                break;

            if (s->poll_msl >= 0 && old_mcr != s->mcr) {

                qemu_chr_fe_ioctl(s->chr,CHR_IOCTL_SERIAL_GET_TIOCM, &flags);

                flags &= ~(CHR_TIOCM_RTS | CHR_TIOCM_DTR);

                if (val & UART_MCR_RTS)
                    flags |= CHR_TIOCM_RTS;
                if (val & UART_MCR_DTR)
                    flags |= CHR_TIOCM_DTR;

                qemu_chr_fe_ioctl(s->chr,CHR_IOCTL_SERIAL_SET_TIOCM, &flags);
                /* Update the modem status after a one-character-send wait-time, since there may be a response
                   from the device/computer at the other end of the serial line */
                qemu_mod_timer(s->modem_status_poll, qemu_get_clock_ns(vm_clock) + s->char_transmit_time);
            }
        }
        break;
    case 5:
        break;
    case 6:
        break;
    case 7:
        s->scr = val;
        break;
    }
}

static uint64_t serial_ioport_read(void *opaque, hwaddr addr, unsigned size)
{
    SerialState *s = opaque;
    uint32_t ret;

    addr &= 7;
    switch(addr) {
    default:
    case 0:
        if (s->lcr & UART_LCR_DLAB) {
            ret = s->divider & 0xff;
        } else {
            if(s->fcr & UART_FCR_FE) {
                ret = fifo_get(s,RECV_FIFO);
                if (s->recv_fifo.count == 0)
                    s->lsr &= ~(UART_LSR_DR | UART_LSR_BI);
                else
                    qemu_mod_timer(s->fifo_timeout_timer, qemu_get_clock_ns (vm_clock) + s->char_transmit_time * 4);
                s->timeout_ipending = 0;
            } else {
                ret = s->rbr;
                s->lsr &= ~(UART_LSR_DR | UART_LSR_BI);
            }
            serial_update_irq(s);
            if (!(s->mcr & UART_MCR_LOOP)) {
                /* in loopback mode, don't receive any data */
                qemu_chr_accept_input(s->chr);
            }
        }
        break;
    case 1:
        if (s->lcr & UART_LCR_DLAB) {
            ret = (s->divider >> 8) & 0xff;
        } else {
            ret = s->ier;
        }
        break;
    case 2:
        ret = s->iir;
        if ((ret & UART_IIR_ID) == UART_IIR_THRI) {
            s->thr_ipending = 0;
            serial_update_irq(s);
        }
        break;
    case 3:
        ret = s->lcr;
        break;
    case 4:
        ret = s->mcr;
        break;
    case 5:
        ret = s->lsr;
        /* Clear break and overrun interrupts */
        if (s->lsr & (UART_LSR_BI|UART_LSR_OE)) {
            s->lsr &= ~(UART_LSR_BI|UART_LSR_OE);
            serial_update_irq(s);
        }
        break;
    case 6:
        if (s->mcr & UART_MCR_LOOP) {
            /* in loopback, the modem output pins are connected to the
               inputs */
            ret = (s->mcr & 0x0c) << 4;
            ret |= (s->mcr & 0x02) << 3;
            ret |= (s->mcr & 0x01) << 5;
        } else {
            if (s->poll_msl >= 0)
                serial_update_msl(s);
            ret = s->msr;
            /* Clear delta bits & msr int after read, if they were set */
            if (s->msr & UART_MSR_ANY_DELTA) {
                s->msr &= 0xF0;
                serial_update_irq(s);
            }
        }
        break;
    case 7:
        ret = s->scr;
        break;
    }
    DPRINTF("read addr=0x%" HWADDR_PRIx " val=0x%02x\n", addr, ret);
    return ret;
}

static int serial_can_receive(SerialState *s)
{
    if(s->fcr & UART_FCR_FE) {
        if(s->recv_fifo.count < UART_FIFO_LENGTH)
        /* Advertise (fifo.itl - fifo.count) bytes when count < ITL, and 1 if above. If UART_FIFO_LENGTH - fifo.count is
        advertised the effect will be to almost always fill the fifo completely before the guest has a chance to respond,
        effectively overriding the ITL that the guest has set. */
             return (s->recv_fifo.count <= s->recv_fifo.itl) ? s->recv_fifo.itl - s->recv_fifo.count : 1;
        else
             return 0;
    } else {
    return !(s->lsr & UART_LSR_DR);
    }
}

static void serial_receive_break(SerialState *s)
{
    s->rbr = 0;
    /* When the LSR_DR is set a null byte is pushed into the fifo */
    fifo_put(s, RECV_FIFO, '\0');
    s->lsr |= UART_LSR_BI | UART_LSR_DR;
    serial_update_irq(s);
}

/* There's data in recv_fifo and s->rbr has not been read for 4 char transmit times */
static void fifo_timeout_int (void *opaque) {
    SerialState *s = opaque;
    if (s->recv_fifo.count) {
        s->timeout_ipending = 1;
        serial_update_irq(s);
    }
}

static int serial_can_receive1(void *opaque)
{
    SerialState *s = opaque;
    return serial_can_receive(s);
}

static void serial_receive1(void *opaque, const uint8_t *buf, int size)
{
    SerialState *s = opaque;

    if (s->wakeup) {
        qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
    }
    if(s->fcr & UART_FCR_FE) {
        int i;
        for (i = 0; i < size; i++) {
            fifo_put(s, RECV_FIFO, buf[i]);
        }
        s->lsr |= UART_LSR_DR;
        /* call the timeout receive callback in 4 char transmit time */
        qemu_mod_timer(s->fifo_timeout_timer, qemu_get_clock_ns (vm_clock) + s->char_transmit_time * 4);
    } else {
        if (s->lsr & UART_LSR_DR)
            s->lsr |= UART_LSR_OE;
        s->rbr = buf[0];
        s->lsr |= UART_LSR_DR;
    }
    serial_update_irq(s);
}

static void serial_event(void *opaque, int event)
{
    SerialState *s = opaque;
    DPRINTF("event %x\n", event);
    if (event == CHR_EVENT_BREAK)
        serial_receive_break(s);
}

static void serial_pre_save(void *opaque)
{
    SerialState *s = opaque;
    s->fcr_vmstate = s->fcr;
}

static int serial_post_load(void *opaque, int version_id)
{
    SerialState *s = opaque;

    if (version_id < 3) {
        s->fcr_vmstate = 0;
    }
    /* Initialize fcr via setter to perform essential side-effects */
    serial_ioport_write(s, 0x02, s->fcr_vmstate, 1);
    serial_update_parameters(s);
    return 0;
}

const VMStateDescription vmstate_serial = {
    .name = "serial",
    .version_id = 3,
    .minimum_version_id = 2,
    .pre_save = serial_pre_save,
    .post_load = serial_post_load,
    .fields      = (VMStateField []) {
        VMSTATE_UINT16_V(divider, SerialState, 2),
        VMSTATE_UINT8(rbr, SerialState),
        VMSTATE_UINT8(ier, SerialState),
        VMSTATE_UINT8(iir, SerialState),
        VMSTATE_UINT8(lcr, SerialState),
        VMSTATE_UINT8(mcr, SerialState),
        VMSTATE_UINT8(lsr, SerialState),
        VMSTATE_UINT8(msr, SerialState),
        VMSTATE_UINT8(scr, SerialState),
        VMSTATE_UINT8_V(fcr_vmstate, SerialState, 3),
        VMSTATE_END_OF_LIST()
    }
};

static void serial_reset(void *opaque)
{
    SerialState *s = opaque;

    s->rbr = 0;
    s->ier = 0;
    s->iir = UART_IIR_NO_INT;
    s->lcr = 0;
    s->lsr = UART_LSR_TEMT | UART_LSR_THRE;
    s->msr = UART_MSR_DCD | UART_MSR_DSR | UART_MSR_CTS;
    /* Default to 9600 baud, 1 start bit, 8 data bits, 1 stop bit, no parity. */
    s->divider = 0x0C;
    s->mcr = UART_MCR_OUT2;
    s->scr = 0;
    s->tsr_retry = 0;
    s->char_transmit_time = (get_ticks_per_sec() / 9600) * 10;
    s->poll_msl = 0;

    fifo_clear(s,RECV_FIFO);
    fifo_clear(s,XMIT_FIFO);

    s->last_xmit_ts = qemu_get_clock_ns(vm_clock);

    s->thr_ipending = 0;
    s->last_break_enable = 0;
    qemu_irq_lower(s->irq);
}

void serial_init_core(SerialState *s)
{
    if (!s->chr) {
        fprintf(stderr, "Can't create serial device, empty char device\n");
	exit(1);
    }

    s->modem_status_poll = qemu_new_timer_ns(vm_clock, (QEMUTimerCB *) serial_update_msl, s);

    s->fifo_timeout_timer = qemu_new_timer_ns(vm_clock, (QEMUTimerCB *) fifo_timeout_int, s);
    qemu_register_reset(serial_reset, s);

    qemu_chr_add_handlers(s->chr, serial_can_receive1, serial_receive1,
                          serial_event, s);
}

void serial_exit_core(SerialState *s)
{
    qemu_chr_add_handlers(s->chr, NULL, NULL, NULL, NULL);
    qemu_unregister_reset(serial_reset, s);
}

/* Change the main reference oscillator frequency. */
void serial_set_frequency(SerialState *s, uint32_t frequency)
{
    s->baudbase = frequency;
    serial_update_parameters(s);
}

const MemoryRegionOps serial_io_ops = {
    .read = serial_ioport_read,
    .write = serial_ioport_write,
    .impl = {
        .min_access_size = 1,
        .max_access_size = 1,
    },
    .endianness = DEVICE_LITTLE_ENDIAN,
};

SerialState *serial_init(int base, qemu_irq irq, int baudbase,
                         CharDriverState *chr, MemoryRegion *system_io)
{
    SerialState *s;

    s = g_malloc0(sizeof(SerialState));

    s->irq = irq;
    s->baudbase = baudbase;
    s->chr = chr;
    serial_init_core(s);

    vmstate_register(NULL, base, &vmstate_serial, s);

    memory_region_init_io(&s->io, &serial_io_ops, s, "serial", 8);
    memory_region_add_subregion(system_io, base, &s->io);

    return s;
}

/* Memory mapped interface */
static uint64_t serial_mm_read(void *opaque, hwaddr addr,
                               unsigned size)
{
    SerialState *s = opaque;
    return serial_ioport_read(s, addr >> s->it_shift, 1);
}

static void serial_mm_write(void *opaque, hwaddr addr,
                            uint64_t value, unsigned size)
{
    SerialState *s = opaque;
    value &= ~0u >> (32 - (size * 8));
    serial_ioport_write(s, addr >> s->it_shift, value, 1);
}

static const MemoryRegionOps serial_mm_ops[3] = {
    [DEVICE_NATIVE_ENDIAN] = {
        .read = serial_mm_read,
        .write = serial_mm_write,
        .endianness = DEVICE_NATIVE_ENDIAN,
    },
    [DEVICE_LITTLE_ENDIAN] = {
        .read = serial_mm_read,
        .write = serial_mm_write,
        .endianness = DEVICE_LITTLE_ENDIAN,
    },
    [DEVICE_BIG_ENDIAN] = {
        .read = serial_mm_read,
        .write = serial_mm_write,
        .endianness = DEVICE_BIG_ENDIAN,
    },
};

SerialState *serial_mm_init(MemoryRegion *address_space,
                            hwaddr base, int it_shift,
                            qemu_irq irq, int baudbase,
                            CharDriverState *chr, enum device_endian end)
{
    SerialState *s;

    s = g_malloc0(sizeof(SerialState));

    s->it_shift = it_shift;
    s->irq = irq;
    s->baudbase = baudbase;
    s->chr = chr;

    serial_init_core(s);
    vmstate_register(NULL, base, &vmstate_serial, s);

    memory_region_init_io(&s->io, &serial_mm_ops[end], s,
                          "serial", 8 << it_shift);
    memory_region_add_subregion(address_space, base, &s->io);

    serial_update_msl(s);
    return s;
}