Linux-2.6.12-rc2

[people/ms/linux.git] / sound / drivers / serial-u16550.c

/*
 *   serial.c
 *   Copyright (c) by Jaroslav Kysela <perex@suse.cz>,
 *                    Isaku Yamahata <yamahata@private.email.ne.jp>,
 *                    George Hansper <ghansper@apana.org.au>,
 *                    Hannu Savolainen
 *
 *   This code is based on the code from ALSA 0.5.9, but heavily rewritten.
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
 *
 * Sat Mar 31 17:27:57 PST 2001 tim.mann@compaq.com 
 *      Added support for the Midiator MS-124T and for the MS-124W in
 *      Single Addressed (S/A) or Multiple Burst (M/B) mode, with
 *      power derived either parasitically from the serial port or
 *      from a separate power supply.
 *
 *      More documentation can be found in serial-u16550.txt.
 */

#include <sound/driver.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/slab.h>
#include <linux/ioport.h>
#include <linux/moduleparam.h>
#include <sound/core.h>
#include <sound/rawmidi.h>
#include <sound/initval.h>

#include <linux/serial_reg.h>

#include <asm/io.h>

MODULE_DESCRIPTION("MIDI serial u16550");
MODULE_LICENSE("GPL");
MODULE_SUPPORTED_DEVICE("{{ALSA, MIDI serial u16550}}");

#define SNDRV_SERIAL_SOUNDCANVAS 0 /* Roland Soundcanvas; F5 NN selects part */
#define SNDRV_SERIAL_MS124T 1      /* Midiator MS-124T */
#define SNDRV_SERIAL_MS124W_SA 2   /* Midiator MS-124W in S/A mode */
#define SNDRV_SERIAL_MS124W_MB 3   /* Midiator MS-124W in M/B mode */
#define SNDRV_SERIAL_GENERIC 4     /* Generic Interface */
#define SNDRV_SERIAL_MAX_ADAPTOR SNDRV_SERIAL_GENERIC
static char *adaptor_names[] = {
        "Soundcanvas",
        "MS-124T",
        "MS-124W S/A",
        "MS-124W M/B",
        "Generic"
};

#define SNDRV_SERIAL_NORMALBUFF 0 /* Normal blocking buffer operation */
#define SNDRV_SERIAL_DROPBUFF   1 /* Non-blocking discard operation */

static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;      /* Index 0-MAX */
static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;       /* ID for this card */
static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE; /* Enable this card */
static long port[SNDRV_CARDS] = SNDRV_DEFAULT_PORT; /* 0x3f8,0x2f8,0x3e8,0x2e8 */
static int irq[SNDRV_CARDS] = SNDRV_DEFAULT_IRQ;        /* 3,4,5,7,9,10,11,14,15 */
static int speed[SNDRV_CARDS] = {[0 ... (SNDRV_CARDS - 1)] = 38400}; /* 9600,19200,38400,57600,115200 */
static int base[SNDRV_CARDS] = {[0 ... (SNDRV_CARDS - 1)] = 115200}; /* baud base */
static int outs[SNDRV_CARDS] = {[0 ... (SNDRV_CARDS - 1)] = 1};  /* 1 to 16 */
static int ins[SNDRV_CARDS] = {[0 ... (SNDRV_CARDS - 1)] = 1};  /* 1 to 16 */
static int adaptor[SNDRV_CARDS] = {[0 ... (SNDRV_CARDS - 1)] = SNDRV_SERIAL_SOUNDCANVAS};
static int droponfull[SNDRV_CARDS] = {[0 ... (SNDRV_CARDS -1)] = SNDRV_SERIAL_NORMALBUFF };

module_param_array(index, int, NULL, 0444);
MODULE_PARM_DESC(index, "Index value for Serial MIDI.");
module_param_array(id, charp, NULL, 0444);
MODULE_PARM_DESC(id, "ID string for Serial MIDI.");
module_param_array(enable, bool, NULL, 0444);
MODULE_PARM_DESC(enable, "Enable UART16550A chip.");
module_param_array(port, long, NULL, 0444);
MODULE_PARM_DESC(port, "Port # for UART16550A chip.");
module_param_array(irq, int, NULL, 0444);
MODULE_PARM_DESC(irq, "IRQ # for UART16550A chip.");
module_param_array(speed, int, NULL, 0444);
MODULE_PARM_DESC(speed, "Speed in bauds.");
module_param_array(base, int, NULL, 0444);
MODULE_PARM_DESC(base, "Base for divisor in bauds.");
module_param_array(outs, int, NULL, 0444);
MODULE_PARM_DESC(outs, "Number of MIDI outputs.");
module_param_array(ins, int, NULL, 0444);
MODULE_PARM_DESC(ins, "Number of MIDI inputs.");
module_param_array(droponfull, bool, NULL, 0444);
MODULE_PARM_DESC(droponfull, "Flag to enable drop-on-full buffer mode");

module_param_array(adaptor, int, NULL, 0444);
MODULE_PARM_DESC(adaptor, "Type of adaptor.");

/*#define SNDRV_SERIAL_MS124W_MB_NOCOMBO 1*/  /* Address outs as 0-3 instead of bitmap */

#define SNDRV_SERIAL_MAX_OUTS   16              /* max 64, min 16 */
#define SNDRV_SERIAL_MAX_INS    16              /* max 64, min 16 */

#define TX_BUFF_SIZE            (1<<15)         /* Must be 2^n */
#define TX_BUFF_MASK            (TX_BUFF_SIZE - 1)

#define SERIAL_MODE_NOT_OPENED          (0)
#define SERIAL_MODE_INPUT_OPEN          (1 << 0)
#define SERIAL_MODE_OUTPUT_OPEN         (1 << 1)
#define SERIAL_MODE_INPUT_TRIGGERED     (1 << 2)
#define SERIAL_MODE_OUTPUT_TRIGGERED    (1 << 3)

typedef struct _snd_uart16550 {
        snd_card_t *card;
        snd_rawmidi_t *rmidi;
        snd_rawmidi_substream_t *midi_output[SNDRV_SERIAL_MAX_OUTS];
        snd_rawmidi_substream_t *midi_input[SNDRV_SERIAL_MAX_INS];

        int filemode;           //open status of file

        spinlock_t open_lock;

        int irq;

        unsigned long base;
        struct resource *res_base;

        unsigned int speed;
        unsigned int speed_base;
        unsigned char divisor;

        unsigned char old_divisor_lsb;
        unsigned char old_divisor_msb;
        unsigned char old_line_ctrl_reg;

        // parameter for using of write loop
        short int fifo_limit;   //used in uart16550
        short int fifo_count;   //used in uart16550

        // type of adaptor
        int adaptor;

        // inputs
        int prev_in;
        unsigned char rstatus;

        // outputs
        int prev_out;
        unsigned char prev_status[SNDRV_SERIAL_MAX_OUTS];

        // write buffer and its writing/reading position
        unsigned char tx_buff[TX_BUFF_SIZE];
        int buff_in_count;
        int buff_in;
        int buff_out;
        int drop_on_full;

        // wait timer
        unsigned int timer_running:1;
        struct timer_list buffer_timer;

} snd_uart16550_t;

static snd_card_t *snd_serial_cards[SNDRV_CARDS] = SNDRV_DEFAULT_PTR;

inline static void snd_uart16550_add_timer(snd_uart16550_t *uart)
{
        if (! uart->timer_running) {
                /* timer 38600bps * 10bit * 16byte */
                uart->buffer_timer.expires = jiffies + (HZ+255)/256;
                uart->timer_running = 1;
                add_timer(&uart->buffer_timer);
        }
}

inline static void snd_uart16550_del_timer(snd_uart16550_t *uart)
{
        if (uart->timer_running) {
                del_timer(&uart->buffer_timer);
                uart->timer_running = 0;
        }
}

/* This macro is only used in snd_uart16550_io_loop */
inline static void snd_uart16550_buffer_output(snd_uart16550_t *uart)
{
        unsigned short buff_out = uart->buff_out;
        if( uart->buff_in_count > 0 ) {
                outb(uart->tx_buff[buff_out], uart->base + UART_TX);
                uart->fifo_count++;
                buff_out++;
                buff_out &= TX_BUFF_MASK;
                uart->buff_out = buff_out;
                uart->buff_in_count--;
        }
}

/* This loop should be called with interrupts disabled
 * We don't want to interrupt this, 
 * as we're already handling an interrupt 
 */
static void snd_uart16550_io_loop(snd_uart16550_t * uart)
{
        unsigned char c, status;
        int substream;

        /* recall previous stream */
        substream = uart->prev_in;

        /* Read Loop */
        while ((status = inb(uart->base + UART_LSR)) & UART_LSR_DR) {
                /* while receive data ready */
                c = inb(uart->base + UART_RX);

                /* keep track of last status byte */
                if (c & 0x80) {
                        uart->rstatus = c;
                }

                /* handle stream switch */
                if (uart->adaptor == SNDRV_SERIAL_GENERIC) {
                        if (uart->rstatus == 0xf5) {
                                if (c <= SNDRV_SERIAL_MAX_INS && c > 0)
                                        substream = c - 1;
                                if (c != 0xf5)
                                        uart->rstatus = 0; /* prevent future bytes from being interpreted as streams */
                        }
                        else if ((uart->filemode & SERIAL_MODE_INPUT_OPEN) && (uart->midi_input[substream] != NULL)) {
                                snd_rawmidi_receive(uart->midi_input[substream], &c, 1);
                        }
                } else if ((uart->filemode & SERIAL_MODE_INPUT_OPEN) && (uart->midi_input[substream] != NULL)) {
                        snd_rawmidi_receive(uart->midi_input[substream], &c, 1);
                }

                if (status & UART_LSR_OE)
                        snd_printk("%s: Overrun on device at 0x%lx\n",
                               uart->rmidi->name, uart->base);
        }

        /* remember the last stream */
        uart->prev_in = substream;

        /* no need of check SERIAL_MODE_OUTPUT_OPEN because if not,
           buffer is never filled. */
        /* Check write status */
        if (status & UART_LSR_THRE) {
                uart->fifo_count = 0;
        }
        if (uart->adaptor == SNDRV_SERIAL_MS124W_SA
           || uart->adaptor == SNDRV_SERIAL_GENERIC) {
                /* Can't use FIFO, must send only when CTS is true */
                status = inb(uart->base + UART_MSR);
                while( (uart->fifo_count == 0) && (status & UART_MSR_CTS) &&
                      (uart->buff_in_count > 0) ) {
                       snd_uart16550_buffer_output(uart);
                       status = inb( uart->base + UART_MSR );
                }
        } else {
                /* Write loop */
                while (uart->fifo_count < uart->fifo_limit      /* Can we write ? */
                       && uart->buff_in_count > 0)      /* Do we want to? */
                        snd_uart16550_buffer_output(uart);
        }
        if (uart->irq < 0 && uart->buff_in_count > 0)
                snd_uart16550_add_timer(uart);
}

/* NOTES ON SERVICING INTERUPTS
 * ---------------------------
 * After receiving a interrupt, it is important to indicate to the UART that
 * this has been done. 
 * For a Rx interrupt, this is done by reading the received byte.
 * For a Tx interrupt this is done by either:
 * a) Writing a byte
 * b) Reading the IIR
 * It is particularly important to read the IIR if a Tx interrupt is received
 * when there is no data in tx_buff[], as in this case there no other
 * indication that the interrupt has been serviced, and it remains outstanding
 * indefinitely. This has the curious side effect that and no further interrupts
 * will be generated from this device AT ALL!!.
 * It is also desirable to clear outstanding interrupts when the device is
 * opened/closed.
 *
 *
 * Note that some devices need OUT2 to be set before they will generate
 * interrupts at all. (Possibly tied to an internal pull-up on CTS?)
 */
static irqreturn_t snd_uart16550_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
        snd_uart16550_t *uart;

        uart = (snd_uart16550_t *) dev_id;
        spin_lock(&uart->open_lock);
        if (uart->filemode == SERIAL_MODE_NOT_OPENED) {
                spin_unlock(&uart->open_lock);
                return IRQ_NONE;
        }
        inb(uart->base + UART_IIR);             /* indicate to the UART that the interrupt has been serviced */
        snd_uart16550_io_loop(uart);
        spin_unlock(&uart->open_lock);
        return IRQ_HANDLED;
}

/* When the polling mode, this function calls snd_uart16550_io_loop. */
static void snd_uart16550_buffer_timer(unsigned long data)
{
        unsigned long flags;
        snd_uart16550_t *uart;

        uart = (snd_uart16550_t *)data;
        spin_lock_irqsave(&uart->open_lock, flags);
        snd_uart16550_del_timer(uart);
        snd_uart16550_io_loop(uart);
        spin_unlock_irqrestore(&uart->open_lock, flags);
}

/*
 *  this method probes, if an uart sits on given port
 *  return 0 if found
 *  return negative error if not found
 */
static int __init snd_uart16550_detect(snd_uart16550_t *uart)
{
        unsigned long io_base = uart->base;
        int ok;
        unsigned char c;

        /* Do some vague tests for the presence of the uart */
        if (io_base == 0 || io_base == SNDRV_AUTO_PORT) {
                return -ENODEV; /* Not configured */
        }

        uart->res_base = request_region(io_base, 8, "Serial MIDI");
        if (uart->res_base == NULL) {
                snd_printk(KERN_ERR "u16550: can't grab port 0x%lx\n", io_base);
                return -EBUSY;
        }

        ok = 1;                 /* uart detected unless one of the following tests should fail */
        /* 8 data-bits, 1 stop-bit, parity off, DLAB = 0 */
        outb(UART_LCR_WLEN8, io_base + UART_LCR); /* Line Control Register */
        c = inb(io_base + UART_IER);
        /* The top four bits of the IER should always == 0 */
        if ((c & 0xf0) != 0)
                ok = 0;         /* failed */

        outb(0xaa, io_base + UART_SCR);
        /* Write arbitrary data into the scratch reg */
        c = inb(io_base + UART_SCR);
        /* If it comes back, it's OK */
        if (c != 0xaa)
                ok = 0;         /* failed */

        outb(0x55, io_base + UART_SCR);
        /* Write arbitrary data into the scratch reg */
        c = inb(io_base + UART_SCR);
        /* If it comes back, it's OK */
        if (c != 0x55)
                ok = 0;         /* failed */

        return ok;
}

static void snd_uart16550_do_open(snd_uart16550_t * uart)
{
        char byte;

        /* Initialize basic variables */
        uart->buff_in_count = 0;
        uart->buff_in = 0;
        uart->buff_out = 0;
        uart->fifo_limit = 1;
        uart->fifo_count = 0;
        uart->timer_running = 0;

        outb(UART_FCR_ENABLE_FIFO       /* Enable FIFO's (if available) */
             | UART_FCR_CLEAR_RCVR      /* Clear receiver FIFO */
             | UART_FCR_CLEAR_XMIT      /* Clear transmitter FIFO */
             | UART_FCR_TRIGGER_4       /* Set FIFO trigger at 4-bytes */
        /* NOTE: interrupt generated after T=(time)4-bytes
         * if less than UART_FCR_TRIGGER bytes received
         */
             ,uart->base + UART_FCR);   /* FIFO Control Register */

        if ((inb(uart->base + UART_IIR) & 0xf0) == 0xc0)
                uart->fifo_limit = 16;
        if (uart->divisor != 0) {
                uart->old_line_ctrl_reg = inb(uart->base + UART_LCR);
                outb(UART_LCR_DLAB      /* Divisor latch access bit */
                     ,uart->base + UART_LCR);   /* Line Control Register */
                uart->old_divisor_lsb = inb(uart->base + UART_DLL);
                uart->old_divisor_msb = inb(uart->base + UART_DLM);

                outb(uart->divisor
                     ,uart->base + UART_DLL);   /* Divisor Latch Low */
                outb(0
                     ,uart->base + UART_DLM);   /* Divisor Latch High */
                /* DLAB is reset to 0 in next outb() */
        }
        /* Set serial parameters (parity off, etc) */
        outb(UART_LCR_WLEN8     /* 8 data-bits */
             | 0                /* 1 stop-bit */
             | 0                /* parity off */
             | 0                /* DLAB = 0 */
             ,uart->base + UART_LCR);   /* Line Control Register */

        switch (uart->adaptor) {
        default:
                outb(UART_MCR_RTS       /* Set Request-To-Send line active */
                     | UART_MCR_DTR     /* Set Data-Terminal-Ready line active */
                     | UART_MCR_OUT2    /* Set OUT2 - not always required, but when
                                         * it is, it is ESSENTIAL for enabling interrupts
                                 */
                     ,uart->base + UART_MCR);   /* Modem Control Register */
                break;
        case SNDRV_SERIAL_MS124W_SA:
        case SNDRV_SERIAL_MS124W_MB:
                /* MS-124W can draw power from RTS and DTR if they
                   are in opposite states. */ 
                outb(UART_MCR_RTS | (0&UART_MCR_DTR) | UART_MCR_OUT2,
                     uart->base + UART_MCR);
                break;
        case SNDRV_SERIAL_MS124T:
                /* MS-124T can draw power from RTS and/or DTR (preferably
                   both) if they are both asserted. */
                outb(UART_MCR_RTS | UART_MCR_DTR | UART_MCR_OUT2,
                     uart->base + UART_MCR);
                break;
        }

        if (uart->irq < 0) {
                byte = (0 & UART_IER_RDI)       /* Disable Receiver data interrupt */
                    |(0 & UART_IER_THRI)        /* Disable Transmitter holding register empty interrupt */
                    ;
        } else if (uart->adaptor == SNDRV_SERIAL_MS124W_SA) {
                byte = UART_IER_RDI     /* Enable Receiver data interrupt */
                    | UART_IER_MSI      /* Enable Modem status interrupt */
                    ;
        } else if (uart->adaptor == SNDRV_SERIAL_GENERIC) {
                byte = UART_IER_RDI     /* Enable Receiver data interrupt */
                    | UART_IER_MSI      /* Enable Modem status interrupt */
                    | UART_IER_THRI     /* Enable Transmitter holding register empty interrupt */
                    ;
        } else {
                byte = UART_IER_RDI     /* Enable Receiver data interrupt */
                    | UART_IER_THRI     /* Enable Transmitter holding register empty interrupt */
                    ;
        }
        outb(byte, uart->base + UART_IER);      /* Interupt enable Register */

        inb(uart->base + UART_LSR);     /* Clear any pre-existing overrun indication */
        inb(uart->base + UART_IIR);     /* Clear any pre-existing transmit interrupt */
        inb(uart->base + UART_RX);      /* Clear any pre-existing receive interrupt */
}

static void snd_uart16550_do_close(snd_uart16550_t * uart)
{
        if (uart->irq < 0)
                snd_uart16550_del_timer(uart);

        /* NOTE: may need to disable interrupts before de-registering out handler.
         * For now, the consequences are harmless.
         */

        outb((0 & UART_IER_RDI)         /* Disable Receiver data interrupt */
             |(0 & UART_IER_THRI)       /* Disable Transmitter holding register empty interrupt */
             ,uart->base + UART_IER);   /* Interupt enable Register */

        switch (uart->adaptor) {
        default:
                outb((0 & UART_MCR_RTS)         /* Deactivate Request-To-Send line  */
                     |(0 & UART_MCR_DTR)        /* Deactivate Data-Terminal-Ready line */
                     |(0 & UART_MCR_OUT2)       /* Deactivate OUT2 */
                     ,uart->base + UART_MCR);   /* Modem Control Register */
          break;
        case SNDRV_SERIAL_MS124W_SA:
        case SNDRV_SERIAL_MS124W_MB:
                /* MS-124W can draw power from RTS and DTR if they
                   are in opposite states; leave it powered. */ 
                outb(UART_MCR_RTS | (0&UART_MCR_DTR) | (0&UART_MCR_OUT2),
                     uart->base + UART_MCR);
                break;
        case SNDRV_SERIAL_MS124T:
                /* MS-124T can draw power from RTS and/or DTR (preferably
                   both) if they are both asserted; leave it powered. */
                outb(UART_MCR_RTS | UART_MCR_DTR | (0&UART_MCR_OUT2),
                     uart->base + UART_MCR);
                break;
        }

        inb(uart->base + UART_IIR);     /* Clear any outstanding interrupts */

        /* Restore old divisor */
        if (uart->divisor != 0) {
                outb(UART_LCR_DLAB              /* Divisor latch access bit */
                     ,uart->base + UART_LCR);   /* Line Control Register */
                outb(uart->old_divisor_lsb
                     ,uart->base + UART_DLL);   /* Divisor Latch Low */
                outb(uart->old_divisor_msb
                     ,uart->base + UART_DLM);   /* Divisor Latch High */
                /* Restore old LCR (data bits, stop bits, parity, DLAB) */
                outb(uart->old_line_ctrl_reg
                     ,uart->base + UART_LCR);   /* Line Control Register */
        }
}

static int snd_uart16550_input_open(snd_rawmidi_substream_t * substream)
{
        unsigned long flags;
        snd_uart16550_t *uart = substream->rmidi->private_data;

        spin_lock_irqsave(&uart->open_lock, flags);
        if (uart->filemode == SERIAL_MODE_NOT_OPENED)
                snd_uart16550_do_open(uart);
        uart->filemode |= SERIAL_MODE_INPUT_OPEN;
        uart->midi_input[substream->number] = substream;
        spin_unlock_irqrestore(&uart->open_lock, flags);
        return 0;
}

static int snd_uart16550_input_close(snd_rawmidi_substream_t * substream)
{
        unsigned long flags;
        snd_uart16550_t *uart = substream->rmidi->private_data;

        spin_lock_irqsave(&uart->open_lock, flags);
        uart->filemode &= ~SERIAL_MODE_INPUT_OPEN;
        uart->midi_input[substream->number] = NULL;
        if (uart->filemode == SERIAL_MODE_NOT_OPENED)
                snd_uart16550_do_close(uart);
        spin_unlock_irqrestore(&uart->open_lock, flags);
        return 0;
}

static void snd_uart16550_input_trigger(snd_rawmidi_substream_t * substream, int up)
{
        unsigned long flags;
        snd_uart16550_t *uart = substream->rmidi->private_data;

        spin_lock_irqsave(&uart->open_lock, flags);
        if (up) {
                uart->filemode |= SERIAL_MODE_INPUT_TRIGGERED;
        } else {
                uart->filemode &= ~SERIAL_MODE_INPUT_TRIGGERED;
        }
        spin_unlock_irqrestore(&uart->open_lock, flags);
}

static int snd_uart16550_output_open(snd_rawmidi_substream_t * substream)
{
        unsigned long flags;
        snd_uart16550_t *uart = substream->rmidi->private_data;

        spin_lock_irqsave(&uart->open_lock, flags);
        if (uart->filemode == SERIAL_MODE_NOT_OPENED)
                snd_uart16550_do_open(uart);
        uart->filemode |= SERIAL_MODE_OUTPUT_OPEN;
        uart->midi_output[substream->number] = substream;
        spin_unlock_irqrestore(&uart->open_lock, flags);
        return 0;
};

static int snd_uart16550_output_close(snd_rawmidi_substream_t * substream)
{
        unsigned long flags;
        snd_uart16550_t *uart = substream->rmidi->private_data;

        spin_lock_irqsave(&uart->open_lock, flags);
        uart->filemode &= ~SERIAL_MODE_OUTPUT_OPEN;
        uart->midi_output[substream->number] = NULL;
        if (uart->filemode == SERIAL_MODE_NOT_OPENED)
                snd_uart16550_do_close(uart);
        spin_unlock_irqrestore(&uart->open_lock, flags);
        return 0;
};

inline static int snd_uart16550_buffer_can_write( snd_uart16550_t *uart, int Num )
{
        if( uart->buff_in_count + Num < TX_BUFF_SIZE )
                return 1;
        else
                return 0;
}

inline static int snd_uart16550_write_buffer(snd_uart16550_t *uart, unsigned char byte)
{
        unsigned short buff_in = uart->buff_in;
        if( uart->buff_in_count < TX_BUFF_SIZE ) {
                uart->tx_buff[buff_in] = byte;
                buff_in++;
                buff_in &= TX_BUFF_MASK;
                uart->buff_in = buff_in;
                uart->buff_in_count++;
                if (uart->irq < 0) /* polling mode */
                        snd_uart16550_add_timer(uart);
                return 1;
        } else
                return 0;
}

static int snd_uart16550_output_byte(snd_uart16550_t *uart, snd_rawmidi_substream_t * substream, unsigned char midi_byte)
{
        if (uart->buff_in_count == 0                            /* Buffer empty? */
            && ((uart->adaptor != SNDRV_SERIAL_MS124W_SA &&
            uart->adaptor != SNDRV_SERIAL_GENERIC) ||
                (uart->fifo_count == 0                               /* FIFO empty? */
                 && (inb(uart->base + UART_MSR) & UART_MSR_CTS)))) { /* CTS? */

                /* Tx Buffer Empty - try to write immediately */
                if ((inb(uart->base + UART_LSR) & UART_LSR_THRE) != 0) {
                        /* Transmitter holding register (and Tx FIFO) empty */
                        uart->fifo_count = 1;
                        outb(midi_byte, uart->base + UART_TX);
                } else {
                        if (uart->fifo_count < uart->fifo_limit) {
                                uart->fifo_count++;
                                outb(midi_byte, uart->base + UART_TX);
                        } else {
                                /* Cannot write (buffer empty) - put char in buffer */
                                snd_uart16550_write_buffer(uart, midi_byte);
                        }
                }
        } else {
                if( !snd_uart16550_write_buffer(uart, midi_byte) ) {
                        snd_printk("%s: Buffer overrun on device at 0x%lx\n",
                                   uart->rmidi->name, uart->base);
                        return 0;
                }
        }

        return 1;
}

static void snd_uart16550_output_write(snd_rawmidi_substream_t * substream)
{
        unsigned long flags;
        unsigned char midi_byte, addr_byte;
        snd_uart16550_t *uart = substream->rmidi->private_data;
        char first;
        static unsigned long lasttime=0;
        
        /* Interupts are disabled during the updating of the tx_buff,
         * since it is 'bad' to have two processes updating the same
         * variables (ie buff_in & buff_out)
         */

        spin_lock_irqsave(&uart->open_lock, flags);

        if (uart->irq < 0)      //polling
                snd_uart16550_io_loop(uart);

        if (uart->adaptor == SNDRV_SERIAL_MS124W_MB) {
                while (1) {
                        /* buffer full? */
                        /* in this mode we need two bytes of space */
                        if (uart->buff_in_count > TX_BUFF_SIZE - 2)
                                break;
                        if (snd_rawmidi_transmit(substream, &midi_byte, 1) != 1)
                                break;
#ifdef SNDRV_SERIAL_MS124W_MB_NOCOMBO
                        /* select exactly one of the four ports */
                        addr_byte = (1 << (substream->number + 4)) | 0x08;
#else
                        /* select any combination of the four ports */
                        addr_byte = (substream->number << 4) | 0x08;
                        /* ...except none */
                        if (addr_byte == 0x08) addr_byte = 0xf8;
#endif
                        snd_uart16550_output_byte(uart, substream, addr_byte);
                        /* send midi byte */
                        snd_uart16550_output_byte(uart, substream, midi_byte);
                }
        } else {
                first = 0;
                while( 1 == snd_rawmidi_transmit_peek(substream, &midi_byte, 1) ) {
                        /* Also send F5 after 3 seconds with no data to handle device disconnect */
                        if (first == 0 && (uart->adaptor == SNDRV_SERIAL_SOUNDCANVAS ||
                                uart->adaptor == SNDRV_SERIAL_GENERIC) &&
                           (uart->prev_out != substream->number || jiffies-lasttime > 3*HZ)) {

                                if( snd_uart16550_buffer_can_write( uart, 3 ) ) {
                                        /* Roland Soundcanvas part selection */
                                        /* If this substream of the data is different previous
                                           substream in this uart, send the change part event */
                                        uart->prev_out = substream->number;
                                        /* change part */
                                        snd_uart16550_output_byte(uart, substream, 0xf5);
                                        /* data */
                                        snd_uart16550_output_byte(uart, substream, uart->prev_out + 1);
                                        /* If midi_byte is a data byte, send the previous status byte */
                                        if ((midi_byte < 0x80) && (uart->adaptor == SNDRV_SERIAL_SOUNDCANVAS))
                                                snd_uart16550_output_byte(uart, substream, uart->prev_status[uart->prev_out]);
                                } else if( !uart->drop_on_full )
                                        break;

                        }

                        /* send midi byte */
                        if( !snd_uart16550_output_byte(uart, substream, midi_byte) && !uart->drop_on_full )
                                break;

                        if (midi_byte >= 0x80 && midi_byte < 0xf0)
                                uart->prev_status[uart->prev_out] = midi_byte;
                        first = 1;

                        snd_rawmidi_transmit_ack( substream, 1 );
                }
                lasttime = jiffies;
        }
        spin_unlock_irqrestore(&uart->open_lock, flags);
}

static void snd_uart16550_output_trigger(snd_rawmidi_substream_t * substream, int up)
{
        unsigned long flags;
        snd_uart16550_t *uart = substream->rmidi->private_data;

        spin_lock_irqsave(&uart->open_lock, flags);
        if (up) {
                uart->filemode |= SERIAL_MODE_OUTPUT_TRIGGERED;
        } else {
                uart->filemode &= ~SERIAL_MODE_OUTPUT_TRIGGERED;
        }
        spin_unlock_irqrestore(&uart->open_lock, flags);
        if (up)
                snd_uart16550_output_write(substream);
}

static snd_rawmidi_ops_t snd_uart16550_output =
{
        .open =         snd_uart16550_output_open,
        .close =        snd_uart16550_output_close,
        .trigger =      snd_uart16550_output_trigger,
};

static snd_rawmidi_ops_t snd_uart16550_input =
{
        .open =         snd_uart16550_input_open,
        .close =        snd_uart16550_input_close,
        .trigger =      snd_uart16550_input_trigger,
};

static int snd_uart16550_free(snd_uart16550_t *uart)
{
        if (uart->irq >= 0)
                free_irq(uart->irq, (void *)uart);
        if (uart->res_base) {
                release_resource(uart->res_base);
                kfree_nocheck(uart->res_base);
        }
        kfree(uart);
        return 0;
};

static int snd_uart16550_dev_free(snd_device_t *device)
{
        snd_uart16550_t *uart = device->device_data;
        return snd_uart16550_free(uart);
}

static int __init snd_uart16550_create(snd_card_t * card,
                                       unsigned long iobase,
                                       int irq,
                                       unsigned int speed,
                                       unsigned int base,
                                       int adaptor,
                                       int droponfull,
                                       snd_uart16550_t **ruart)
{
        static snd_device_ops_t ops = {
                .dev_free =     snd_uart16550_dev_free,
        };
        snd_uart16550_t *uart;
        int err;


        if ((uart = kcalloc(1, sizeof(*uart), GFP_KERNEL)) == NULL)
                return -ENOMEM;
        uart->adaptor = adaptor;
        uart->card = card;
        spin_lock_init(&uart->open_lock);
        uart->irq = -1;
        uart->base = iobase;
        uart->drop_on_full = droponfull;

        if ((err = snd_uart16550_detect(uart)) <= 0) {
                printk(KERN_ERR "no UART detected at 0x%lx\n", iobase);
                return err;
        }

        if (irq >= 0 && irq != SNDRV_AUTO_IRQ) {
                if (request_irq(irq, snd_uart16550_interrupt,
                                SA_INTERRUPT, "Serial MIDI", (void *) uart)) {
                        snd_printk("irq %d busy. Using Polling.\n", irq);
                } else {
                        uart->irq = irq;
                }
        }
        uart->divisor = base / speed;
        uart->speed = base / (unsigned int)uart->divisor;
        uart->speed_base = base;
        uart->prev_out = -1;
        uart->prev_in = 0;
        uart->rstatus = 0;
        memset(uart->prev_status, 0x80, sizeof(unsigned char) * SNDRV_SERIAL_MAX_OUTS);
        init_timer(&uart->buffer_timer);
        uart->buffer_timer.function = snd_uart16550_buffer_timer;
        uart->buffer_timer.data = (unsigned long)uart;
        uart->timer_running = 0;

        /* Register device */
        if ((err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, uart, &ops)) < 0) {
                snd_uart16550_free(uart);
                return err;
        }

        switch (uart->adaptor) {
        case SNDRV_SERIAL_MS124W_SA:
        case SNDRV_SERIAL_MS124W_MB:
                /* MS-124W can draw power from RTS and DTR if they
                   are in opposite states. */ 
                outb(UART_MCR_RTS | (0&UART_MCR_DTR), uart->base + UART_MCR);
                break;
        case SNDRV_SERIAL_MS124T:
                /* MS-124T can draw power from RTS and/or DTR (preferably
                   both) if they are asserted. */
                outb(UART_MCR_RTS | UART_MCR_DTR, uart->base + UART_MCR);
                break;
        default:
                break;
        }

        if (ruart)
                *ruart = uart;

        return 0;
}

static void __init snd_uart16550_substreams(snd_rawmidi_str_t *stream)
{
        struct list_head *list;

        list_for_each(list, &stream->substreams) {
                snd_rawmidi_substream_t *substream = list_entry(list, snd_rawmidi_substream_t, list);
                sprintf(substream->name, "Serial MIDI %d", substream->number + 1);
        }
}

static int __init snd_uart16550_rmidi(snd_uart16550_t *uart, int device, int outs, int ins, snd_rawmidi_t **rmidi)
{
        snd_rawmidi_t *rrawmidi;
        int err;

        if ((err = snd_rawmidi_new(uart->card, "UART Serial MIDI", device, outs, ins, &rrawmidi)) < 0)
                return err;
        snd_rawmidi_set_ops(rrawmidi, SNDRV_RAWMIDI_STREAM_INPUT, &snd_uart16550_input);
        snd_rawmidi_set_ops(rrawmidi, SNDRV_RAWMIDI_STREAM_OUTPUT, &snd_uart16550_output);
        strcpy(rrawmidi->name, "Serial MIDI");
        snd_uart16550_substreams(&rrawmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT]);
        snd_uart16550_substreams(&rrawmidi->streams[SNDRV_RAWMIDI_STREAM_INPUT]);
        rrawmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT |
                               SNDRV_RAWMIDI_INFO_INPUT |
                               SNDRV_RAWMIDI_INFO_DUPLEX;
        rrawmidi->private_data = uart;
        if (rmidi)
                *rmidi = rrawmidi;
        return 0;
}

static int __init snd_serial_probe(int dev)
{
        snd_card_t *card;
        snd_uart16550_t *uart;
        int err;

        if (!enable[dev])
                return -ENOENT;

        switch (adaptor[dev]) {
        case SNDRV_SERIAL_SOUNDCANVAS:
                ins[dev] = 1;
                break;
        case SNDRV_SERIAL_MS124T:
        case SNDRV_SERIAL_MS124W_SA:
                outs[dev] = 1;
                ins[dev] = 1;
                break;
        case SNDRV_SERIAL_MS124W_MB:
                outs[dev] = 16;
                ins[dev] = 1;
                break;
        case SNDRV_SERIAL_GENERIC:
                break;
        default:
                snd_printk("Adaptor type is out of range 0-%d (%d)\n",
                           SNDRV_SERIAL_MAX_ADAPTOR, adaptor[dev]);
                return -ENODEV;
        }

        if (outs[dev] < 1 || outs[dev] > SNDRV_SERIAL_MAX_OUTS) {
                snd_printk("Count of outputs is out of range 1-%d (%d)\n",
                           SNDRV_SERIAL_MAX_OUTS, outs[dev]);
                return -ENODEV;
        }

        if (ins[dev] < 1 || ins[dev] > SNDRV_SERIAL_MAX_INS) {
                snd_printk("Count of inputs is out of range 1-%d (%d)\n",
                           SNDRV_SERIAL_MAX_INS, ins[dev]);
                return -ENODEV;
        }

        card  = snd_card_new(index[dev], id[dev], THIS_MODULE, 0);
        if (card == NULL)
                return -ENOMEM;

        strcpy(card->driver, "Serial");
        strcpy(card->shortname, "Serial MIDI (UART16550A)");

        if ((err = snd_uart16550_create(card,
                                        port[dev],
                                        irq[dev],
                                        speed[dev],
                                        base[dev],
                                        adaptor[dev],
                                        droponfull[dev],
                                        &uart)) < 0) {
                snd_card_free(card);
                return err;
        }

        if ((err = snd_uart16550_rmidi(uart, 0, outs[dev], ins[dev], &uart->rmidi)) < 0) {
                snd_card_free(card);
                return err;
        }

        sprintf(card->longname, "%s at 0x%lx, irq %d speed %d div %d outs %d ins %d adaptor %s droponfull %d",
                card->shortname,
                uart->base,
                uart->irq,
                uart->speed,
                (int)uart->divisor,
                outs[dev],
                ins[dev],
                adaptor_names[uart->adaptor],
                uart->drop_on_full);

        if ((err = snd_card_register(card)) < 0) {
                snd_card_free(card);
                return err;
        }
        snd_serial_cards[dev] = card;
        return 0;
}

static int __init alsa_card_serial_init(void)
{
        int dev = 0;
        int cards = 0;

        for (dev = 0; dev < SNDRV_CARDS; dev++) {
                if (snd_serial_probe(dev) == 0)
                        cards++;
        }

        if (cards == 0) {
#ifdef MODULE
                printk(KERN_ERR "serial midi soundcard not found or device busy\n");
#endif
                return -ENODEV;
        }
        return 0;
}

static void __exit alsa_card_serial_exit(void)
{
        int dev;

        for (dev = 0; dev < SNDRV_CARDS; dev++) {
                if (snd_serial_cards[dev] != NULL)
                        snd_card_free(snd_serial_cards[dev]);
        }
}

module_init(alsa_card_serial_init)
module_exit(alsa_card_serial_exit)