serial.c.bak

一份精简的linux内核源代码

/*
 *  linux/kernel/serial.c
 *
 *  (C) 1991  Linus Torvalds
 */

/*
 *	serial.c
 *
 * This module implements the rs232 io functions
 *	void rs_write(struct tty_struct * queue);
 *	void rs_init(void);
 * and all interrupts pertaining to serial IO.
 */

#include <linux/tty.h>
#include <linux/sched.h>
#include <asm/system.h>
#include <asm/io.h>

#define WAKEUP_CHARS (TTY_BUF_SIZE/4)/*当写队列中含有WAKEUP_CHARS时就开始发送*/

extern void rs1_interrupt(void);
extern void rs2_interrupt(void);

static void init(int port)/*初始化串行端口*/
{
	outb_p(0x80,port+3);	/* set DLAB of line control reg */
	outb_p(0x30,port);	/* LS of divisor (48 -> 2400 bps */
	outb_p(0x00,port+1);	/* MS of divisor */
	outb_p(0x03,port+3);	/* reset DLAB */
	outb_p(0x0b,port+4);	/* set DTR,RTS, OUT_2 */
	outb_p(0x0d,port+1);	/* enable all intrs but writes */
	(void)inb(port);	/* read data port to reset things (?) */
}

void rs_init(void)/*初始化串行设备*/
{
	set_intr_gate(0x24,rs1_interrupt);/*设置串口1的中断向量*/
	set_intr_gate(0x23,rs2_interrupt);/*设置串口2的中断向量*/
	init(tty_table[1].read_q.data);/*初始化串口1（.data为端口的基地址）*/
	init(tty_table[2].read_q.data);/*初始化串口2*/
	outb(inb_p(0x21)&0xE7,0x21);
}

/*
 * This routine gets called when tty_write has put something into
 * the write_queue. It must check wheter the queue is empty, and
 * set the interrupt register accordingly
 *
 *	void _rs_write(struct tty_struct * tty);
 */
void rs_write(struct tty_struct * tty)/*串行数据发送输出（仅开启发送保持寄存器已空中断标志，此后当发送保持寄存器空时，UART就会产生中断请求，随后中断处理程序将会取走寄存器中的数据，随即UART又会产生中断，直到写队列为空位置）*/
{
	cli();
	if (!EMPTY(tty->write_q))
		outb(inb_p(tty->write_q.data+1)|0x02,tty->write_q.data+1);
	sti();
}