/*
 *	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 */		//線控制寄存器，將第7位置1是開放除法因子鎖存器地址位
	outb_p(0x30,port);	/* LS of divisor (48 -> 2400 bps */	//將波特率設為2400（低有效位）
	outb_p(0x00,port+1);	/* MS of divisor */				//將波特率的最高有效位保存入該寄存器
	outb_p(0x03,port+3);	/* reset DLAB */				//將DLAB設為0，幀設為8位（通常是8位）
	outb_p(0x0b,port+4);	/* set DTR,RTS, OUT_2 */			//設置數據終端準備好線（DTR）的狀態，設置請求發送線（RTS）的狀態，out_2用于開放中斷請求
	outb_p(0x0d,port+1);	/* enable all intrs but writes */
	(void)inb(port);	/* read data port to reset things (?) */	//獲取接收緩沖區數據字節
}

void rs_init(void)
{
	set_intr_gate(0x24,rs1_interrupt);			//串行口端口3F8的中斷好是0x24
	set_intr_gate(0x23,rs2_interrupt);			//串行口端口2F8的中斷好是0x23
	init(tty_table[1].read_q.data);			//初始化2個串行端口
	init(tty_table[2].read_q.data);
	outb(inb_p(0x21)&0xE7,0x21);			//控制中斷控制器對中斷請求線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);	//將寄存器的第2位（傳送位）置1，開放傳送中斷
	sti();
}