#include <stdio.h>
void timer8253(void);
int read8253(void);
void zero8253(void);
int main()
{
int time;
while(1)
{
timer8253();
sleep (1);
printf("coutnt =%d",read8253());	
}	
	
}

void timer8253(void)
{
	asm("cli");			//disable hardware interrupts
	outb(0x76,0x43);     //send mode to mode register               
	outb(0xFF,0x41);     //set lsb	
	outb(0xFF,0x41);     //set msb
	asm("sti");			//enable hardware interrupts
}



int read8253(void)
{
	int time=0;
	// reads the time in ticks into CounterValue
	asm(
    "xor     %eax,%eax \n\t"
    "in      $0x41,%al \n\t"         //least significant byte
    "jmp (+2) \n\t"//    QDELAY
    //"jmp $+2 \n\t"
    "mov	%al,%ah \n\t"
    "in	$0x41,%al \n\t"	//most significant byte
    "xchg	%al,%ah \n\t"
    "mov     $0xffff,%ebx \n\t"
    "sub     %eax,%ebx \n\t"
    "mov     %ebx,%0 \n\t"
	:"=a"(time)
	:%eax,%ebx	
	); 
	//code :output :input :used registers
    zero8253();
	return time;

}
void zero8253(void)
{
    //actually sets counter to ffffh
     asm(
	"jmp (+2) \n\t"
	"mov     $0x0ff,al \n\t"
	"out	%al,$0x40 \n\t"
	"jmp (+2)\n\t"
 	"out	%al, $0x40"
	:%eax
	);
}

here is what the sgnals look like.
_   ____
 | |    |  =0
 |_|    |
 S      S

_      _
 |    | |  =1
 |____| |
 S      S

So a one is at least ten times longer low from start to stop.

for(int i=0;i<9;i++)
{
while(port is high)high++;
while(port is low)low++;
if (high >10*low)byte|(1<<i);
}

foreach bit{
    loop( while no start edge )
    grab time[start]
    loop( while no data edge )
    grab time[data]
    loop( while no stop edge )
    grab time[stop]
    if( ( time[stop] - time[data] ) < 10 * ( time[data] - time[start] ) ) then
        bit = 1
     else
        bit = 0
     endif
}