source: rtems/c/src/lib/libcpu/sh/sh7750/sci/sh4uart.c @ ba71076

/*
 * Generic UART Serial driver for SH-4 processors
 *
 * This driver uses variable SH4_CPU_HZ_Frequency, 
 * which should be defined in bsp to HZ macro.
 *
 * Copyright (C) 2000 OKTET Ltd., St.-Petersburg, Russian Fed.
 * Author: Alexandra Kossovsky <sasha@oktet.ru>
 *
 *  COPYRIGHT (c) 1989-2000.
 *  On-Line Applications Research Corporation (OAR).
 *  Copyright assigned to U.S. Government, 1994.
 *
 *  The license and distribution terms for this file may be
 *  found in the file LICENSE in this distribution or at
 *
 *  http://www.OARcorp.com/rtems/license.html.
 *
 *  $Id$
 *
 */

#include <rtems.h>
#include <termios.h>
#include <rtems/libio.h>
#include "sh/sh4uart.h"

#ifndef SH4_UART_INTERRUPT_LEVEL
#define SH4_UART_INTERRUPT_LEVEL 4
#endif

/* Forward function declarations */
static rtems_isr
sh4uart1_interrupt_transmit(rtems_vector_number vec);
static rtems_isr
sh4uart1_interrupt_receive(rtems_vector_number vec);
static rtems_isr
sh4uart2_interrupt_transmit(rtems_vector_number vec);
static rtems_isr
sh4uart2_interrupt_receive(rtems_vector_number vec);

/*
 * sh4uart_init --
 * This function verifies the input parameters and perform initialization
 *     of the SH-4 on-chip UART descriptor structure.
 *
 * PARAMETERS:
 *     uart - pointer to the UART channel descriptor structure
 *     tty - pointer to termios structure
 *     chn - channel number (SH4_SCI/SH4_SCIF -- 1/2)
 *     int_driven - interrupt-driven (1) or polled (0) I/O mode
 *
 * RETURNS:
 *     RTEMS_SUCCESSFUL if all parameters are valid, or error code
 */
rtems_status_code
sh4uart_init(sh4uart *uart, void *tty, int chn, int int_driven)
{
    if (uart == NULL)
        return RTEMS_INVALID_ADDRESS;

    if ((chn != SH4_SCI) && (chn != SH4_SCIF))
                return RTEMS_INVALID_NUMBER;

    uart->chn = chn;
    uart->tty = tty;
    uart->int_driven = int_driven;

#if 0
    sh4uart_poll_write(uart, "init", 4);
#endif
    return RTEMS_SUCCESSFUL;
}

/*
 * sh4uart_get_Pph --
 *    Get current peripheral module clock.
 *    
 * PARAMETERS: none;
 *    Cpu clock is get from SH4_CPU_HZ_Frequency.
 *    This variable should be defined in bsp.
 *
 * RETURNS:
 *    peripheral module clock in Hz.
 */
rtems_unsigned32
sh4uart_get_Pph(void)
{
    rtems_unsigned16 frqcr = *(volatile rtems_unsigned16 *)SH7750_FRQCR;
    rtems_unsigned32 Pph = SH4_CPU_HZ_Frequency;

    switch (frqcr & SH7750_FRQCR_IFC)
    {
        case SH7750_FRQCR_IFCDIV1:
            break;

        case SH7750_FRQCR_IFCDIV2:
            Pph *= 2;
            break;

        case SH7750_FRQCR_IFCDIV3:
            Pph *= 3;
            break;

        case SH7750_FRQCR_IFCDIV4:
            Pph *= 4;
            break;

        case SH7750_FRQCR_IFCDIV6:
            Pph *= 6;
            break;

        case SH7750_FRQCR_IFCDIV8:
            Pph *= 8;
            break;

        default: /* unreachable */
            break;
    }
    
    switch (frqcr & SH7750_FRQCR_PFC)
    {
        case SH7750_FRQCR_PFCDIV2:
            Pph /= 2;
            break;

        case SH7750_FRQCR_PFCDIV3:
            Pph /= 3;
            break;

        case SH7750_FRQCR_PFCDIV4:
            Pph /= 4;
            break;

        case SH7750_FRQCR_PFCDIV6:
            Pph /= 6;
            break;

        case SH7750_FRQCR_PFCDIV8:
            Pph /= 8;
            break;

        default: /* unreachable */
            break;
    }

    return Pph;
}

/*
 * sh4uart_set_baudrate --
 *     Program the UART timer to specified baudrate
 *
 * PARAMETERS:
 *     uart - pointer to UART descriptor structure
 *     baud - termios baud rate (B50, B9600, etc...)
 *
 * ALGORITHM:
 *     see SH7750 Hardware Manual.
 *
 * RETURNS:
 *     none
 */
static void
sh4uart_set_baudrate(sh4uart *uart, speed_t baud)
{
    rtems_unsigned32 rate;
    rtems_signed16 div;
    int n;
    rtems_unsigned32 Pph = sh4uart_get_Pph();

    switch (baud)
    {
        case B50:     rate = 50; break;
        case B75:     rate = 75; break;
        case B110:    rate = 110; break;
        case B134:    rate = 134; break;
        case B150:    rate = 150; break;
        case B200:    rate = 200; break;
        case B300:    rate = 300; break;
        case B600:    rate = 600; break;
        case B1200:   rate = 1200; break;
        case B2400:   rate = 2400; break;
        case B4800:   rate = 4800; break;
        case B9600:   rate = 9600; break;
        case B19200:  rate = 19200; break;
        case B38400:  rate = 38400; break;
        case B57600:  rate = 57600; break;
#ifdef B115200
        case B115200: rate = 115200; break;
#endif
#ifdef B230400
        case B230400: rate = 230400; break;
#endif
        default:      rate = 9600; break;
    }

    for (n = 0; n < 4; n++)
    {
        div = Pph / (32 * (1 << (2 * n)) * rate) - 1;
        if (div < 0x100)
            break;
    }

    /* Set default baudrate if specified baudrate is impossible */
    if (n >= 4)
        sh4uart_set_baudrate(uart, B9600);
    
    SCSMR(uart->chn) &= ~SH7750_SCSMR_CKS;
    SCSMR(uart->chn) |= n << SH7750_SCSMR_CKS_S;
    SCBRR(uart->chn) = div;
    /* Whait at least 1 bit interwal */
    rtems_task_wake_after(RTEMS_MILLISECONDS_TO_TICKS(1000 / rate));
}

/*
 * sh4uart_reset --
 *     This function perform the hardware initialization of SH-4
 *     on-chip UART controller using parameters
 *     filled by the sh4uart_init function.
 *
 * PARAMETERS:
 *     uart - pointer to UART channel descriptor structure
 *
 * RETURNS:
 *     RTEMS_SUCCESSFUL if channel is initialized successfully, error
 *     code in other case
 */
rtems_status_code
sh4uart_reset(sh4uart *uart)
{
    register int chn;
    register int int_driven;
    rtems_status_code rc;

    if (uart == NULL)
        return RTEMS_INVALID_ADDRESS;

    chn = uart->chn;
    int_driven = uart->int_driven;

    SCSCR(chn) = 0x0;       /* Is set properly at the end of this function */
    SCSMR(chn) = 0x0;       /* 8-bit, non-parity, 1 stop bit, pf/1 clock */

    if (chn == SH4_SCIF)
        SCFCR2 = SH7750_SCFCR2_TFRST | SH7750_SCFCR2_RFRST | 
                SH7750_SCFCR2_RTRG_1 | SH7750_SCFCR2_TTRG_4;

    if (chn == SH4_SCI)
        SCSPTR1 = int_driven ? 0x0 : SH7750_SCSPTR1_EIO;
    else
        SCSPTR2 = SH7750_SCSPTR2_RTSDT;

    if (int_driven)
    {
        rtems_unsigned16 ipr;

        if (chn == SH4_SCI)
        {
            ipr = IPRB;
            ipr &= ~SH7750_IPRB_SCI1;
            ipr |= SH4_UART_INTERRUPT_LEVEL << SH7750_IPRB_SCI1_S;
            IPRB = ipr;

            rc = rtems_interrupt_catch(sh4uart1_interrupt_transmit, 
                    SH7750_EVT_TO_NUM(SH7750_EVT_SCI_TXI), 
                    &uart->old_handler_transmit);
            if (rc != RTEMS_SUCCESSFUL)
                return rc;
            rc = rtems_interrupt_catch(sh4uart1_interrupt_receive, 
                    SH7750_EVT_TO_NUM(SH7750_EVT_SCI_RXI), 
                    &uart->old_handler_receive);
            if (rc != RTEMS_SUCCESSFUL)
                return rc;
        }
        else
        {
            ipr = IPRC;
            ipr &= ~SH7750_IPRC_SCIF;
            ipr |= SH4_UART_INTERRUPT_LEVEL << SH7750_IPRC_SCIF_S;
            IPRC = ipr;

            rc = rtems_interrupt_catch(sh4uart2_interrupt_transmit, 
                    SH7750_EVT_TO_NUM(SH7750_EVT_SCIF_TXI), 
                    &uart->old_handler_transmit);
            if (rc != RTEMS_SUCCESSFUL)
                return rc;
            rc = rtems_interrupt_catch(sh4uart2_interrupt_receive, 
                    SH7750_EVT_TO_NUM(SH7750_EVT_SCIF_RXI), 
                    &uart->old_handler_receive);
            if (rc != RTEMS_SUCCESSFUL)
                return rc;
        }
        uart->tx_buf = NULL;
        uart->tx_ptr = uart->tx_buf_len = 0;
    }

    sh4uart_set_baudrate(uart, B38400); /* debug defaults (unfortunately,
                                           it is differ to termios default */

    SCSCR(chn) = SH7750_SCSCR_TE | SH7750_SCSCR_RE | 
            (chn == SH4_SCI ? 0x0 : SH7750_SCSCR2_REIE) | 
            (int_driven ? (SH7750_SCSCR_RIE | SH7750_SCSCR_TIE) : 0x0);
                    
    return RTEMS_SUCCESSFUL;
}

/*
 * sh4uart_disable --
 *     This function disable the operations on SH-4 UART controller
 *
 * PARAMETERS:
 *     uart - pointer to UART channel descriptor structure
 *
 * RETURNS:
 *     RTEMS_SUCCESSFUL if UART closed successfuly, or error code in
 *     other case
 */
rtems_status_code
sh4uart_disable(sh4uart *uart)
{
    rtems_status_code rc;

    SCSCR(uart->chn) &= ~(SH7750_SCSCR_TE | SH7750_SCSCR_RE);

    if (uart->int_driven)
    {
        rc = rtems_interrupt_catch(uart->old_handler_transmit, 
                uart->chn == SH4_SCI ? 
                        SH7750_EVT_SCI_TXI : SH7750_EVT_SCIF_TXI, 
                NULL);
        if (rc != RTEMS_SUCCESSFUL)
            return rc;
        rc = rtems_interrupt_catch(uart->old_handler_receive, 
                uart->chn == SH4_SCI ? 
                        SH7750_EVT_SCI_RXI : SH7750_EVT_SCIF_RXI, 
                NULL);
        if (rc != RTEMS_SUCCESSFUL)
            return rc;
    }

    return RTEMS_SUCCESSFUL;
}

/*
 * sh4uart_set_attributes --
 *     This function parse the termios attributes structure and perform
 *     the appropriate settings in hardware.
 *
 * PARAMETERS:
 *     uart - pointer to the UART descriptor structure
 *     t - pointer to termios parameters
 *
 * RETURNS:
 *     RTEMS_SUCCESSFUL
 */
rtems_status_code
sh4uart_set_attributes(sh4uart *uart, const struct termios *t)
{
    int level;
    speed_t baud;
    rtems_unsigned16 smr;
   
    smr = (rtems_unsigned16)(*(rtems_unsigned8 *)SH7750_SCSMR(uart->chn));

    baud = cfgetospeed(t);

    /* Set flow control XXX*/
    if ((t->c_cflag & CRTSCTS) != 0)
    {
    }

    /* Set character size -- only 7 or 8 bit */
    switch (t->c_cflag & CSIZE)
    {
        case CS5:
        case CS6:
        case CS7: smr |= SH7750_SCSMR_CHR_7; break;
        case CS8: smr &= ~SH7750_SCSMR_CHR_7; break;
    }

    /* Set number of stop bits */
    if ((t->c_cflag & CSTOPB) != 0)
        smr |= SH7750_SCSMR_STOP_2;
    else
        smr &= ~SH7750_SCSMR_STOP_2;

    /* Set parity mode */
    if ((t->c_cflag & PARENB) != 0)
    {
        smr |= SH7750_SCSMR_PE;
        if ((t->c_cflag & PARODD) != 0)
           smr |= SH7750_SCSMR_PM_ODD;
        else
           smr &= ~SH7750_SCSMR_PM_ODD;
    }
    else
        smr &= ~SH7750_SCSMR_PE;

    rtems_interrupt_disable(level);
    /* wait untill all data is transmitted */
    rtems_task_wake_after(RTEMS_MILLISECONDS_TO_TICKS(100));
    /* disable operations */
    SCSCR(uart->chn) &= ~(SH7750_SCSCR_TE | SH7750_SCSCR_RE);

    sh4uart_set_baudrate(uart, baud);
    SCSMR(uart->chn) = (rtems_unsigned8)smr;

    /* enable operations */
    SCSCR(uart->chn) |= SH7750_SCSCR_TE | SH7750_SCSCR_RE;
    rtems_interrupt_enable(level);

    return RTEMS_SUCCESSFUL;
}

/*
 * sh4uart_handle_error --
 *     Perfoms error (Overrun, Framing & Parity) handling
 *
 * PARAMETERS:
 *     uart - pointer to UART descriptor structure
 *
 * RETURNS:
 *     nothing
 */
void
sh4uart_handle_error(sh4uart *uart)
{
#if 0
    int status_reg = SCSSR(uart->chn);
#endif

    if(uart->chn == SH4_SCI)
    {
        SCSSR1 &= ~(SH7750_SCSSR1_ORER | SH7750_SCSSR1_FER | SH7750_SCSSR1_PER);
    }
    else
    {
        SCSSR2 &= ~(SH7750_SCSSR2_ER | SH7750_SCSSR2_BRK | SH7750_SCSSR2_FER);
        SCLSR2 &= ~(SH7750_SCLSR2_ORER);
    }
}

/*
 * sh4uart_poll_read --
 *     This function tried to read character from SH-4 UART and perform
 *     error handling. When parity or framing error occured, return
 *     value dependent on termios input mode flags:
 *         - received character, if IGNPAR == 1
 *         - 0, if IGNPAR == 0 and PARMRK == 0
 *         - 0xff and 0x00 on next poll_read invocation, if IGNPAR == 0 and
 *           PARMRK == 1
 *
 * PARAMETERS:
 *     uart - pointer to UART descriptor structure
 *
 * RETURNS:
 *     code of received character or -1 if no characters received.
 */
int
sh4uart_poll_read(sh4uart *uart)
{
    int chn = uart->chn;
    int error_occured = 0;
    int parity_error = 0;
    int break_occured = 0;
    int ch;

    if (uart->parerr_mark_flag == 1)
    {
        uart->parerr_mark_flag = 0;
        return 0;
    }

    if (chn == SH4_SCI)
    {
        if ((SCSSR1 & (SH7750_SCSSR1_PER | SH7750_SCSSR1_FER | 
                     SH7750_SCSSR1_ORER)) != 0)
        {
            error_occured = 1;
            if (SCSSR1 & (SH7750_SCSSR1_PER | SH7750_SCSSR1_FER))
                parity_error = 1;
            sh4uart_handle_error(uart);
        }
        if ((SCSSR1 & SH7750_SCSSR1_RDRF) == 0)
            return -1;
    }
    else
    {
        if ((SCSSR2 & (SH7750_SCSSR2_ER | SH7750_SCSSR2_DR |
                     SH7750_SCSSR2_BRK)) != 0 || 
                (SCLSR2 & SH7750_SCLSR2_ORER) != 0)
        {
            error_occured = 1;
            if (SCSSR2 & (SH7750_SCSSR1_PER | SH7750_SCSSR1_FER))
                parity_error = 1;
            if (SCSSR2 & SH7750_SCSSR2_BRK)
                break_occured = 1;
            sh4uart_handle_error(uart);
        }
        if ((SCSSR2 & SH7750_SCSSR2_RDF) == 0)
            return -1;
    }

    if (parity_error && !(uart->c_iflag & IGNPAR))
    {
        if (uart->c_iflag & PARMRK)
        {
            uart->parerr_mark_flag = 1;
            return 0xff;
        }
        else
            return 0;
    }

    if (break_occured && !(uart->c_iflag & BRKINT))
    {
        if (uart->c_iflag & IGNBRK)
            return 0;
        else
            return 0;   /* XXX -- SIGINT */
    }

    ch = SCRDR(chn);
    if (uart->chn == SH4_SCI)
        SCSSR1 &= ~SH7750_SCSSR1_RDRF;
    else
        SCSSR2 &= ~SH7750_SCSSR2_RDF;

    return ch;
}

/*
 * sh4uart_poll_write --
 *     This function transmit buffer byte-by-byte in polling mode.
 *
 * PARAMETERS:
 *     uart - pointer to the UART descriptor structure
 *     buf - pointer to transmit buffer
 *     len - transmit buffer length
 *
 * RETURNS:
 *     0
 */
int
sh4uart_poll_write(sh4uart *uart, const char *buf, int len)
{
    while (len)
    {
        if (uart->chn == SH4_SCI)
        {
            while ((SCSSR1 & SH7750_SCSSR1_TDRE) != 0)
            {
                SCTDR1 = *buf++;
                len--;
                SCSSR1 &= ~SH7750_SCSSR1_TDRE;
            }
        }
        else
        {
            while ((SCSSR2 & SH7750_SCSSR2_TDFE) != 0)
            {
                int i;
                for (i = 0; 
                        i < 16 - TRANSMIT_TRIGGER_VALUE(SCFCR2 & 
                            SH7750_SCFCR2_TTRG); 
                        i++)
                {
                    SCTDR2 = *buf++;
                    len--;
                }
                while ((SCSSR2 & SH7750_SCSSR2_TDFE) == 0 || 
                        (SCSSR2 & SH7750_SCSSR2_TEND) == 0);
                    SCSSR2 &= ~(SH7750_SCSSR1_TDRE | SH7750_SCSSR2_TEND);
            }
        }
    }
    return 0;
}

/**********************************
 * Functions to handle interrupts *
 **********************************/
/* sh4uart1_interrupt_receive --
 *     UART interrupt handler routine -- SCI
 *     Receiving data
 *
 * PARAMETERS:
 *     vec - interrupt vector number
 *
 * RETURNS:
 *     none
 */
static rtems_isr
sh4uart1_interrupt_receive(rtems_vector_number vec)
{
    register int bp = 0;
    char buf[32];

    /* Find UART descriptor from vector number */
    sh4uart *uart = &sh4_uarts[0];

    while (1)
    {
        if ((bp < sizeof(buf) - 1) && ((SCSSR1 & SH7750_SCSSR1_RDRF) != 0))
        {
            /* Receive character and handle frame/parity errors */
            if ((SCSSR1 & (SH7750_SCSSR1_PER | SH7750_SCSSR1_FER | 
                            SH7750_SCSSR1_ORER)) != 0)
            {
                if (SCSSR1 & (SH7750_SCSSR1_PER | SH7750_SCSSR1_FER))
                {
                    if(!(uart->c_iflag & IGNPAR))
                    {
                        if (uart->c_iflag & PARMRK)
                        {
                            buf[bp++] = 0xff;
                            buf[bp++] = 0x00;
                        }
                        else
                            buf[bp++] = 0x00;
                    }
                    else
                        buf[bp++] = SCRDR1;
                }
                sh4uart_handle_error(uart);
            }
            else
                buf[bp++] = SCRDR1;
            SCSSR1 &= ~SH7750_SCSSR1_RDRF;
        }
        else
        {
            if (bp != 0)
                rtems_termios_enqueue_raw_characters(uart->tty, buf, bp);
            break;
        }
    }
}

/* sh4uart2_interrupt_receive --
 *     UART interrupt handler routine -- SCIF
 *     Receiving data
 *
 * PARAMETERS:
 *     vec - interrupt vector number
 *
 * RETURNS:
 *     none
 */
static rtems_isr
sh4uart2_interrupt_receive(rtems_vector_number vec)
{
    register int bp = 0;
    char buf[32];

    /* Find UART descriptor from vector number */
    sh4uart *uart = &sh4_uarts[1];

    while (1)
    {
        if ((bp < sizeof(buf) - 1) && ((SCSSR2 & SH7750_SCSSR2_RDF) != 0))
        {
            if ((SCSSR2 & (SH7750_SCSSR2_ER | SH7750_SCSSR2_DR |
                            SH7750_SCSSR2_BRK)) != 0 || 
                    (SH7750_SCLSR2 & SH7750_SCLSR2_ORER) != 0)
            {
                if (SCSSR2 & SH7750_SCSSR2_ER)
                {
                    if(!(uart->c_iflag & IGNPAR))
                    {
                        if (uart->c_iflag & PARMRK)
                        {
                            buf[bp++] = 0xff;
                            buf[bp++] = 0x00;
                        }
                        else
                            buf[bp++] = 0x00;
                    }
                    else
                        buf[bp++] = SCRDR1;
                }

                if (SCSSR2 & SH7750_SCSSR2_BRK)
                {
                    if (uart->c_iflag & IGNBRK)
                        buf[bp++] = 0x00;
                    else
                        buf[bp++] = 0x00;   /* XXX -- SIGINT */
                }
                    
                sh4uart_handle_error(uart);
            }
            else
                buf[bp++] = SCRDR1;
            SCSSR2 &= ~SH7750_SCSSR2_RDF;
        }
        else
        {
            if (bp != 0)
                rtems_termios_enqueue_raw_characters(uart->tty, buf, bp);
            break;
        }
    }
}


/* sh4uart1_interrupt_transmit --
 *     UART interrupt handler routine -- SCI
 *     It continues transmit data when old part of data is transmitted
 *
 * PARAMETERS:
 *     vec - interrupt vector number
 *
 * RETURNS:
 *     none
 */
static rtems_isr
sh4uart1_interrupt_transmit(rtems_vector_number vec)
{
    /* Find UART descriptor from vector number */
    sh4uart *uart = &sh4_uarts[0];

    if (uart->tx_buf != NULL && uart->tx_ptr < uart->tx_buf_len)
    {
        while ((SCSSR1 & SH7750_SCSSR1_TDRE) != 0 && 
                uart->tx_ptr < uart->tx_buf_len)
        {
            SCTDR1 = uart->tx_buf[uart->tx_ptr++];
            SCSSR1 &= ~SH7750_SCSSR1_TDRE;
        }
    }
    else
    {
        register int dequeue = uart->tx_buf_len;

        uart->tx_buf = NULL;
        uart->tx_ptr = uart->tx_buf_len = 0;

        /* Disable interrupts while we do not have any data to transmit */
        SCSCR1 &= ~SH7750_SCSCR_TIE;

        rtems_termios_dequeue_characters(uart->tty, dequeue);
    }
}

/* sh4uart2_interrupt_transmit --
 *     UART interrupt handler routine -- SCI
 *     It continues transmit data when old part of data is transmitted
 *
 * PARAMETERS:
 *     vec - interrupt vector number
 *
 * RETURNS:
 *     none
 */
static rtems_isr
sh4uart2_interrupt_transmit(rtems_vector_number vec)
{
    /* Find UART descriptor from vector number */
    sh4uart *uart = &sh4_uarts[1];

    if (uart->tx_buf != NULL && uart->tx_ptr < uart->tx_buf_len)
    {
            while ((SCSSR2 & SH7750_SCSSR2_TDFE) != 0)
            {
                int i;
                for (i = 0; 
                        i < 16 - TRANSMIT_TRIGGER_VALUE(SCFCR2 & 
                            SH7750_SCFCR2_TTRG); 
                        i++)
                    SCTDR2 = uart->tx_buf[uart->tx_ptr++];
                while ((SCSSR1 & SH7750_SCSSR1_TDRE) == 0 ||
                        (SCSSR1 & SH7750_SCSSR1_TEND) == 0);
                    SCSSR1 &= ~(SH7750_SCSSR1_TDRE | SH7750_SCSSR2_TEND);
            }
    }
    else
    {
        register int dequeue = uart->tx_buf_len;

        uart->tx_buf = NULL;
        uart->tx_ptr = uart->tx_buf_len = 0;

        /* Disable interrupts while we do not have any data to transmit */
        SCSCR2 &= ~SH7750_SCSCR_TIE;

        rtems_termios_dequeue_characters(uart->tty, dequeue);
    }
}

/* sh4uart_interrupt_write --
 *     This function initiate transmitting of the buffer in interrupt mode.
 *
 * PARAMETERS:
 *     uart - pointer to the UART descriptor structure
 *     buf - pointer to transmit buffer
 *     len - transmit buffer length
 *
 * RETURNS:
 *     0
 */
rtems_status_code
sh4uart_interrupt_write(sh4uart *uart, const char *buf, int len)
{
    int level;

    while ((SCSSR1 & SH7750_SCSSR1_TEND) == 0);

    rtems_interrupt_disable(level);
    
    uart->tx_buf = buf;
    uart->tx_buf_len = len;
    uart->tx_ptr = 0;

    if (uart->chn == SH4_SCI)
    {
        SCSCR1 |= SH7750_SCSCR_TIE;
    }
    else
        SCSCR2 |= SH7750_SCSCR_TIE;

    rtems_interrupt_enable(level);

    return RTEMS_SUCCESSFUL;
}

/* sh4uart_stop_remote_tx --
 *     This function stop data flow from remote device.
 *
 * PARAMETERS:
 *     uart - pointer to the UART descriptor structure
 *
 * RETURNS:
 *     RTEMS_SUCCESSFUL
 */
rtems_status_code
sh4uart_stop_remote_tx(sh4uart *uart)
{
    SCSCR(uart->chn) &= ~(SH7750_SCSCR_RIE | SH7750_SCSCR_RE);
    return RTEMS_SUCCESSFUL;
}

/* sh4uart_start_remote_tx --
 *     This function resume data flow from remote device.
 *
 * PARAMETERS:
 *     uart - pointer to the UART descriptor structure
 *
 * RETURNS:
 *     RTEMS_SUCCESSFUL
 */
rtems_status_code
sh4uart_start_remote_tx(sh4uart *uart)
{
    SCSCR(uart->chn) |= SH7750_SCSCR_RIE | SH7750_SCSCR_RE;
    return RTEMS_SUCCESSFUL;
}

#ifdef SH4_WITH_IPL
/*********************************
 * Functions for SH-IPL gdb stub *
 *********************************/

/*
 * ipl_finish --
 *     Says gdb that program finished to get out from it.
 */
extern void ipl_finish(void);
asm(
"   .global _ipl_finish\n"
"_ipl_finish:\n"
"   mov.l   __ipl_finish_value, r0\n"
"   trapa   #0x3f\n"
"   nop\n"
"   rts\n"
"   nop\n"
"   .align 4\n"
"__ipl_finish_value:\n"
"   .long   255"
);

extern int ipl_serial_input(int poll_count);
asm(
"    .global _ipl_serial_input\n"
"_ipl_serial_input:\n"
"    mov  #1,r0\n"
"    trapa #0x3f\n"
"    nop\n"
"    rts\n"
"    nop\n");

extern void ipl_serial_output(const char *buf, int len);
asm (
"    .global _ipl_serial_output\n"
"_ipl_serial_output:\n"
"    mov  #0,r0\n"
"    trapa #0x3f\n"
"    nop\n"
"    rts\n"
"    nop\n");

/* ipl_console_poll_read --
 *     poll read operation for simulator console through ipl mechanism.
 *
 * PARAMETERS:
 *     minor - minor device number
 *
 * RETURNS:
 *     character code red from UART, or -1 if there is no characters
 *     available
 */
int
ipl_console_poll_read(int minor)
{
    unsigned char buf;
    buf = ipl_serial_input(0x100000);
    return buf;
}

/* ipl_console_poll_write --
 *     wrapper for polling mode write function
 *
 * PARAMETERS:
 *     minor - minor device number
 *     buf - output buffer
 *     len - output buffer length
 *
 * RETURNS:
 *     result code (0)
 */
int
ipl_console_poll_write(int minor, const char *buf, int len)
{
    int c;
    while (len > 0) 
    {
        c = (len < 64 ? len : 64);
        ipl_serial_output(buf, c);
        len -= c;
        buf += c;
    }
    return 0;
}
#endif