自学教程：C++ write_sbdchn函数代码示例

static void sbd_console_write(struct console *co, const char *s,			      unsigned int count){	int chip = co->index / DUART_MAX_SIDE;	int side = co->index % DUART_MAX_SIDE;	struct sbd_port *sport = &sbd_duarts[chip].sport[side];	struct uart_port *uport = &sport->port;	unsigned long flags;	unsigned int mask;	/* Disable transmit interrupts and enable the transmitter. */	spin_lock_irqsave(&uport->lock, flags);	mask = read_sbdshr(sport, R_DUART_IMRREG((uport->line) % 2));	write_sbdshr(sport, R_DUART_IMRREG((uport->line) % 2),		     mask & ~M_DUART_IMR_TX);	write_sbdchn(sport, R_DUART_CMD, M_DUART_TX_EN);	spin_unlock_irqrestore(&uport->lock, flags);	uart_console_write(&sport->port, s, count, sbd_console_putchar);	/* Restore transmit interrupts and the transmitter enable. */	spin_lock_irqsave(&uport->lock, flags);	sbd_line_drain(sport);	if (sport->tx_stopped)		write_sbdchn(sport, R_DUART_CMD, M_DUART_TX_DIS);	write_sbdshr(sport, R_DUART_IMRREG((uport->line) % 2), mask);	spin_unlock_irqrestore(&uport->lock, flags);}

static int sbd_startup(struct uart_port *uport){	struct sbd_port *sport = to_sport(uport);	unsigned int mode1;	int ret;	ret = request_irq(sport->port.irq, sbd_interrupt,			  IRQF_SHARED, "sb1250-duart", sport);	if (ret)		return ret;	/* Clear the receive FIFO.  */	sbd_receive_drain(sport);	/* Clear the interrupt registers.  */	write_sbdchn(sport, R_DUART_CMD, V_DUART_MISC_CMD_RESET_BREAK_INT);	read_sbdshr(sport, R_DUART_INCHREG((uport->line) % 2));	/* Set rx/tx interrupt to FIFO available.  */	mode1 = read_sbdchn(sport, R_DUART_MODE_REG_1);	mode1 &= ~(M_DUART_RX_IRQ_SEL_RXFULL | M_DUART_TX_IRQ_SEL_TXEMPT);	write_sbdchn(sport, R_DUART_MODE_REG_1, mode1);	/* Disable tx, enable rx.  */	write_sbdchn(sport, R_DUART_CMD, M_DUART_TX_DIS | M_DUART_RX_EN);	sport->tx_stopped = 1;	/* Enable interrupts.  */	write_sbdshr(sport, R_DUART_IMRREG((uport->line) % 2),		     M_DUART_IMR_IN | M_DUART_IMR_RX);	return 0;}

static void sbd_break_ctl(struct uart_port *uport, int break_state){	struct sbd_port *sport = to_sport(uport);	if (break_state == -1)		write_sbdchn(sport, R_DUART_CMD, V_DUART_MISC_CMD_START_BREAK);	else		write_sbdchn(sport, R_DUART_CMD, V_DUART_MISC_CMD_STOP_BREAK);}

/* * Serial console stuff.  Very basic, polling driver for doing serial * console output.  The console_lock is held by the caller, so we * shouldn't be interrupted for more console activity. */static void sbd_console_putchar(struct uart_port *uport, int ch){	struct sbd_port *sport = to_sport(uport);	sbd_transmit_drain(sport);	write_sbdchn(sport, R_DUART_TX_HOLD, ch);}

static void sbd_enable_ms(struct uart_port *uport){	struct sbd_port *sport = to_sport(uport);	write_sbdchn(sport, R_DUART_AUXCTL_X,		     M_DUART_CIN_CHNG_ENA | M_DUART_CTS_CHNG_ENA);}

static void sbd_stop_tx(struct uart_port *uport){	struct sbd_port *sport = to_sport(uport);	write_sbdchn(sport, R_DUART_CMD, M_DUART_TX_DIS);	sport->tx_stopped = 1;};

static void sbd_set_mctrl(struct uart_port *uport, unsigned int mctrl){	struct sbd_port *sport = to_sport(uport);	unsigned int clr = 0, set = 0, mode2;	if (mctrl & TIOCM_DTR)		set |= M_DUART_SET_OPR2;	else		clr |= M_DUART_CLR_OPR2;	if (mctrl & TIOCM_RTS)		set |= M_DUART_SET_OPR0;	else		clr |= M_DUART_CLR_OPR0;	clr <<= (uport->line) % 2;	set <<= (uport->line) % 2;	mode2 = read_sbdchn(sport, R_DUART_MODE_REG_2);	mode2 &= ~M_DUART_CHAN_MODE;	if (mctrl & TIOCM_LOOP)		mode2 |= V_DUART_CHAN_MODE_LCL_LOOP;	else		mode2 |= V_DUART_CHAN_MODE_NORMAL;	write_sbdshr(sport, R_DUART_CLEAR_OPR, clr);	write_sbdshr(sport, R_DUART_SET_OPR, set);	write_sbdchn(sport, R_DUART_MODE_REG_2, mode2);}

static void sbd_shutdown(struct uart_port *uport){	struct sbd_port *sport = to_sport(uport);	write_sbdchn(sport, R_DUART_CMD, M_DUART_TX_DIS | M_DUART_RX_DIS);	sport->tx_stopped = 1;	free_irq(sport->port.irq, sport);}

static void sbd_start_tx(struct uart_port *uport){	struct sbd_port *sport = to_sport(uport);	unsigned int mask;	/* Enable tx interrupts.  */	mask = read_sbdshr(sport, R_DUART_IMRREG((uport->line) % 2));	mask |= M_DUART_IMR_TX;	write_sbdshr(sport, R_DUART_IMRREG((uport->line) % 2), mask);	/* Go!, go!, go!...  */	write_sbdchn(sport, R_DUART_CMD, M_DUART_TX_EN);	sport->tx_stopped = 0;};

static void sbd_transmit_chars(struct sbd_port *sport){	struct uart_port *uport = &sport->port;	struct circ_buf *xmit = &sport->port.state->xmit;	unsigned int mask;	int stop_tx;	/* XON/XOFF chars.  */	if (sport->port.x_char) {		write_sbdchn(sport, R_DUART_TX_HOLD, sport->port.x_char);		sport->port.icount.tx++;		sport->port.x_char = 0;		return;	}	/* If nothing to do or stopped or hardware stopped.  */	stop_tx = (uart_circ_empty(xmit) || uart_tx_stopped(&sport->port));	/* Send char.  */	if (!stop_tx) {		write_sbdchn(sport, R_DUART_TX_HOLD, xmit->buf[xmit->tail]);		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);		sport->port.icount.tx++;		if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)			uart_write_wakeup(&sport->port);	}	/* Are we are done?  */	if (stop_tx || uart_circ_empty(xmit)) {		/* Disable tx interrupts.  */		mask = read_sbdshr(sport, R_DUART_IMRREG((uport->line) % 2));		mask &= ~M_DUART_IMR_TX;		write_sbdshr(sport, R_DUART_IMRREG((uport->line) % 2), mask);	}}

static void sbd_init_port(struct sbd_port *sport){	struct uart_port *uport = &sport->port;	if (sport->initialised)		return;	/* There is no DUART reset feature, so just set some sane defaults.  */	write_sbdchn(sport, R_DUART_CMD, V_DUART_MISC_CMD_RESET_TX);	write_sbdchn(sport, R_DUART_CMD, V_DUART_MISC_CMD_RESET_RX);	write_sbdchn(sport, R_DUART_MODE_REG_1, V_DUART_BITS_PER_CHAR_8);	write_sbdchn(sport, R_DUART_MODE_REG_2, 0);	write_sbdchn(sport, R_DUART_FULL_CTL,		     V_DUART_INT_TIME(0) | V_DUART_SIG_FULL(15));	write_sbdchn(sport, R_DUART_OPCR_X, 0);	write_sbdchn(sport, R_DUART_AUXCTL_X, 0);	write_sbdshr(sport, R_DUART_IMRREG((uport->line) % 2), 0);	sport->initialised = 1;}

static void sbd_set_termios(struct uart_port *uport, struct ktermios *termios,			    struct ktermios *old_termios){	struct sbd_port *sport = to_sport(uport);	unsigned int mode1 = 0, mode2 = 0, aux = 0;	unsigned int mode1mask = 0, mode2mask = 0, auxmask = 0;	unsigned int oldmode1, oldmode2, oldaux;	unsigned int baud, brg;	unsigned int command;	mode1mask |= ~(M_DUART_PARITY_MODE | M_DUART_PARITY_TYPE_ODD |		       M_DUART_BITS_PER_CHAR);	mode2mask |= ~M_DUART_STOP_BIT_LEN_2;	auxmask |= ~M_DUART_CTS_CHNG_ENA;	/* Byte size.  */	switch (termios->c_cflag & CSIZE) {	case CS5:	case CS6:		/* Unsupported, leave unchanged.  */		mode1mask |= M_DUART_PARITY_MODE;		break;	case CS7:		mode1 |= V_DUART_BITS_PER_CHAR_7;		break;	case CS8:	default:		mode1 |= V_DUART_BITS_PER_CHAR_8;		break;	}	/* Parity and stop bits.  */	if (termios->c_cflag & CSTOPB)		mode2 |= M_DUART_STOP_BIT_LEN_2;	else		mode2 |= M_DUART_STOP_BIT_LEN_1;	if (termios->c_cflag & PARENB)		mode1 |= V_DUART_PARITY_MODE_ADD;	else		mode1 |= V_DUART_PARITY_MODE_NONE;	if (termios->c_cflag & PARODD)		mode1 |= M_DUART_PARITY_TYPE_ODD;	else		mode1 |= M_DUART_PARITY_TYPE_EVEN;	baud = uart_get_baud_rate(uport, termios, old_termios, 1200, 5000000);	brg = V_DUART_BAUD_RATE(baud);	/* The actual lower bound is 1221bps, so compensate.  */	if (brg > M_DUART_CLK_COUNTER)		brg = M_DUART_CLK_COUNTER;	uart_update_timeout(uport, termios->c_cflag, baud);	uport->read_status_mask = M_DUART_OVRUN_ERR;	if (termios->c_iflag & INPCK)		uport->read_status_mask |= M_DUART_FRM_ERR |					   M_DUART_PARITY_ERR;	if (termios->c_iflag & (BRKINT | PARMRK))		uport->read_status_mask |= M_DUART_RCVD_BRK;	uport->ignore_status_mask = 0;	if (termios->c_iflag & IGNPAR)		uport->ignore_status_mask |= M_DUART_FRM_ERR |					     M_DUART_PARITY_ERR;	if (termios->c_iflag & IGNBRK) {		uport->ignore_status_mask |= M_DUART_RCVD_BRK;		if (termios->c_iflag & IGNPAR)			uport->ignore_status_mask |= M_DUART_OVRUN_ERR;	}	if (termios->c_cflag & CREAD)		command = M_DUART_RX_EN;	else		command = M_DUART_RX_DIS;	if (termios->c_cflag & CRTSCTS)		aux |= M_DUART_CTS_CHNG_ENA;	else		aux &= ~M_DUART_CTS_CHNG_ENA;	spin_lock(&uport->lock);	if (sport->tx_stopped)		command |= M_DUART_TX_DIS;	else		command |= M_DUART_TX_EN;	oldmode1 = read_sbdchn(sport, R_DUART_MODE_REG_1) & mode1mask;	oldmode2 = read_sbdchn(sport, R_DUART_MODE_REG_2) & mode2mask;	oldaux = read_sbdchn(sport, R_DUART_AUXCTL_X) & auxmask;	if (!sport->tx_stopped)		sbd_line_drain(sport);	write_sbdchn(sport, R_DUART_CMD, M_DUART_TX_DIS | M_DUART_RX_DIS);	write_sbdchn(sport, R_DUART_MODE_REG_1, mode1 | oldmode1);	write_sbdchn(sport, R_DUART_MODE_REG_2, mode2 | oldmode2);	write_sbdchn(sport, R_DUART_CLK_SEL, brg);	write_sbdchn(sport, R_DUART_AUXCTL_X, aux | oldaux);//.........这里部分代码省略.........