__________________________________________________________
../kernel/Serial.c
__________________________________________________________
/*
* 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)
extern void rs1_interrupt(void);
extern void rs2_interrupt(void);
static void init(int port)
{
outb_p(0x80,port+3); /* set DLAB of line control reg */ //线控制寄存器，将第7位置1是开放除法因子锁存器地址位
outb_p(0x30,port); /* LS of divisor (48 -> 2400 bps */ //将波特率设为2400（低有效位）
outb_p(0x00,port+1); /* MS of divisor */ //将波特率的最高有效位保存入该寄存器
outb_p(0x03,port+3); /* reset DLAB */ //将DLAB设为0，幀设为8位（通常是8位）
outb_p(0x0b,port+4); /* set DTR,RTS, OUT_2 */ //设置数据终端准备好线（DTR）的状态，设置请求发送线（RTS）的状态，out_2用于开放中断请求
outb_p(0x0d,port+1); /* enable all intrs but writes */
(void)inb(port); /* read data port to reset things (?) */ //获取接收缓冲区数据字节
}
void rs_init(void)
{
set_intr_gate(0x24,rs1_interrupt); //串行口端口3F8的中断好是0x24
set_intr_gate(0x23,rs2_interrupt); //串行口端口2F8的中断好是0x23
init(tty_table[1].read_q.data); //初始化2个串行端口
init(tty_table[2].read_q.data);
outb(inb_p(0x21)&0xE7,0x21); //控制中断控制器对中断请求线0--7的操作
}
/*
* 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)
{
cli();
if (!EMPTY(tty->write_q))
outb(inb_p(tty->write_q.data+1)|0x02,tty->write_q.data+1); //将寄存器的第2位（传送位）置1，开放传送中断
sti();
}
