RTEMS: Counting time, again... (help)

[sashti srinivasan]

Hello Alex,
   If your BSP is PC386,..., here is the source code I
use for my purpose.  It takes a timeval structure(with
resolution of CONFIGURE_MICROSECONDS_PER_TICK)
obtained from gettimeofday and updates it by reading
the hardware register.  The macros used here are
defined in <bsp.h> and you have to include that.  If
you find it incorrect or has bugs, please let me know.

  Note: The routine HardwareUpdate(), is accurate upto
1 Microsecond.  Also note that this routine assumes
Microseconds per tick is set at 10 milliseconds.  If
it is different, change the source accordingly.

int globalAddress;
char globalValue;
struct timeval tempTime;
struct timezone noUse;
/* Routine to write a byte to PC IO port
 * CS02M040 Srinivasan, IIT(M)
 */
void WriteByte(int address,char value)
{
        globalAddress=address;
        globalValue=value;
        asm("movl globalAddress,%edx");
        asm("movb globalValue,%al");
        asm("outb %al,%dx");
}

/* Routine to read a byte from PC IO port
 * CS02M040 Srinivasan, IIT(M)
 */
char ReadByte(int address)
{
        char value;
        globalAddress=address;
        asm("movl globalAddress,%edx");
        asm("movb %dl,globalValue");
        asm("inb %dx,%al");
        asm("movb %al,globalValue");
        value=globalValue;
        return value;
}

/* Routine that returns time with 1 microsecond 
 * accuracy(On PC hardware).  This routine calls
 * gettimeofday again. 
 * CS02M040 S Srinivasan, IIT(M)
 */
void HardwareUpdate(struct timeval *inp)
{
   unsigned long currentValue;
   unsigned char lsb,msb;
   unsigned long nextValue;
   currentValue=inp->tv_usec;
   WriteByte(TIMER_MODE,TIMER_SEL0|TIMER_LATCH);
   lsb=ReadByte(TIMER_CNTR0);
   msb=ReadByte(TIMER_CNTR0);
   gettimeofday(&tempTime,&noUse);
   if(tempTime.tv_usec!=inp->tv_usec)
   {
      *inp=tempTime;
      currentValue=inp->tv_usec;
      WriteByte(TIMER_MODE,TIMER_SEL0|TIMER_LATCH);
      lsb=ReadByte(TIMER_CNTR0);
      msb=ReadByte(TIMER_CNTR0);
   }
   nextValue=((unsigned long)lsb) + ((unsigned
long)msb)*256;
   nextValue=TICK_TO_US(nextValue);
   nextValue=10000-nextValue;
   if(nextValue>=10005)
   {
     printf("Error in low level time functions %d
\n",nextValue);
     exit(0);
   }
   if(nextValue+currentValue>=1000000)
   {
      nextValue=(nextValue+currentValue)%1000000;
      inp->tv_sec++;
   }
   else
   {
      nextValue=nextValue+currentValue;
   }
   inp->tv_usec=nextValue;
}

Regards
Srinivasan
--- Alex <kbyte at iol.pt> wrote:
> Hi,
> 
> I know that will be some users that will say to me
> that this doubt is already explain in the mailling
> list, but before sent this mail I search in the
> mailling list and I saw nothings...
> 
> Weel, I need to measure time in microseconds (or
> nanoseconds, this will be great). Using the posix
> calls the maximum resolution I get is 20
> milliseconds. That doesnt feet my needs... :-(
> 
> So, I thinking to use an osciloscope or some device
> like that to measure those times.
> Another idea is to access the hardware ticks.
> 
> Which is the best way to measure those times?
> External counter device or access hardware ticker?
> 
> Is there any free source code to access the hardware
> ticks?
> 
> Thanks in advance...
> 
> BSP: i686
> 
> Alex
> 
> 
>
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