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From: philippe <philippe DOT meynard AT vendeeconcept DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: jitter between 2 hardware interrupt
Date: Wed, 3 Mar 2010 02:25:52 -0800 (PST)
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Hi, everybody.
I have a problem with the jitter between hardware interrupt. I use the
real time clock interrupt at 1024 interrupt by second. But I have
jitter between 2 interrupt. Normaly I must have 976us betwwen and i
have 310us to 1641 us occasionally. I have test on multiple PC but its
the same problem. My PC is a Celeron M at 1.6Ghz under FreeDOS without
driver launch at boot.
See my program to test it:
"
#include <dpmi.h>
#include <sys/nearptr.h>
#include <sys/farptr.h>
#include <go32.h>
#include <crt0.h>
#include <io.h>
#include <pc.h>

#include "irq.h"

typedef unsigned long long uint64;

short *ptrbasevid;
uint64
tpsinterclock,tpsinterclockmemo,tpsinterclockmin,tpsinterclockmax,passtpsinterclock;
uint64 debclock_precis,finclock_precis;

long interbcleexpl=0;
long valitexploit=0;

int testtempsbcleit(void);
int proginter0(void);
int proginter1(void);
void miseenplace(void);
int proginteritgen1ms(void);
DECL_END_OF_FUNCTION(proginteritgen1ms);
short affchaine(const char *chaine,short positvid);
short affchaine_2(const char *chaine,short positvid);
short affchiffre2(long chiff,short positvid);
short affchiffre2inch(long chiff,short positch,char *ptrch);
uint64 get_rdtsc (void);

int _crt0_startup_flags=_CRT0_FLAG_LOCK_MEMORY |
_CRT0_FLAG_NONMOVE_SBRK;

int proginter0(void)
{
	outportb(0x20,0x20);
	return(0);
}
static END_OF_FUNCTION(proginter0);

__dpmi_paddr addr_proginter1;

int proginter1(void)
{
	return(0);
}
static END_OF_FUNCTION(proginter1);

int main(void)
{
	__djgpp_nearptr_enable();
	ptrbasevid=(short *)(0x0b8000 + __djgpp_conventional_base);
	affchaine("depart",80);
	miseenplace();
	return(0);
}

void miseenplace(void)
{
	int i;

	outportb(0x21,0xFF);
	outportb(0xA1,0xFF);

	LOCK_FUNCTION(proginter0);
	LOCK_FUNCTION(proginter1);
	addr_proginter1.selector = _my_cs();
	addr_proginter1.offset32 = (long)proginter1;

	for(i=0x00;i<=0x07;i++){
		__dpmi_set_protected_mode_interrupt_vector(i, &addr_proginter1);
	}

	_install_irq(0x08,proginter0);
	_install_irq(0x09,proginter0);
	_install_irq(0x0A,proginter0);
	_install_irq(0x0B,proginter0);
	_install_irq(0x0C,proginter0);
	_install_irq(0x0D,proginter0);
	_install_irq(0x0E,proginter0);
	_install_irq(0x0F,proginter0);

	LOCK_FUNCTION(proginteritgen1ms);
	_install_irq(0x70,proginteritgen1ms);

	LOCK_VARIABLE(interbcleexpl) ;

	outportb(0x70,0x0b);
	outportb(0x71,0x42);
	outportb(0x70,0x0c);
	inportb(0x71);

	_install_irq(0x71,proginter0);
	_install_irq(0x72,proginter0);
	_install_irq(0x73,proginter0);
	_install_irq(0x74,proginter0);
	_install_irq(0x75,proginter0);
	_install_irq(0x76,proginter0);
	_install_irq(0x77,proginter0);
	for(i=0x10;i<=0x30;i++){
		__dpmi_set_protected_mode_interrupt_vector(i, &addr_proginter1);
	}
	for(i=0x32;i<=0x6F;i++){
		__dpmi_set_protected_mode_interrupt_vector(i, &addr_proginter1);
	}

	for(i=0x78;i<=0xFF;i++){
		__dpmi_set_protected_mode_interrupt_vector(i, &addr_proginter1);
	}

	__dpmi_set_protected_mode_interrupt_vector(0x31, &addr_proginter1);

	outportb(0x21,0xFB);//irq 2 valide
	outportb(0xA1,0xFE);
	testtempsbcleit();
}

int testtempsbcleit(void)
{
	tpsinterclockmin=0;
	tpsinterclockmax=0;
	interbcleexpl=0;
	valitexploit=1;
	passtpsinterclock=0;

	while(1){
		if(interbcleexpl>=500){
			affchaine("     ",80);
			affchiffre2((long)tpsinterclockmin/1000,80);
			affchiffre2((long)tpsinterclockmax/1000,160);
			interbcleexpl=0;
		}
	}
	return(1);
}

int proginteritgen1ms(void)
{
	if(valitexploit){
		interbcleexpl++;
		debclock_precis=get_rdtsc();
		passtpsinterclock++;
		if(passtpsinterclock<10000){
			tpsinterclockmemo=debclock_precis;
		}
		else{
			tpsinterclock=debclock_precis-tpsinterclockmemo;
			tpsinterclockmemo=debclock_precis;
			if(!tpsinterclockmin) tpsinterclockmin=tpsinterclock;
			if(!tpsinterclockmax) tpsinterclockmax=tpsinterclock;
			if(tpsinterclock<tpsinterclockmin) tpsinterclockmin=tpsinterclock;
			if(tpsinterclock>tpsinterclockmax) tpsinterclockmax=tpsinterclock;
		}
	}

	outportb(0x70,0x0c);
	inportb(0x71);

	outportb(0x20,0x20);
	outportb(0xA0,0x20);

	return 0;
}

END_OF_FUNCTION(proginteritgen1ms);


uint64 get_rdtsc (void)
  {
    register unsigned long long tsc;
    __asm__ __volatile__ (
              ".byte 0x0F, 0x31;"   // rdtsc opcode
            : "=A" (tsc) );
    return (tsc);
  }

short affchaine(const char *chaine,short positvid)
{
	return(affchaine_2(chaine,positvid));
}

short affchaine_2(const char *chaine,short positvid)
{
	short *ptrvideo;
	char att;

	ptrvideo=ptrbasevid;
	while((att=*chaine)!=0){
		*(ptrvideo+positvid)=(unsigned char)att+7*256;
		positvid++;
		chaine++;
	}
	return(positvid);
}


short affchiffre2(long chiff,short positvid)
{
	char chchiff[10];
	short lgchiff;

	lgchiff=affchiffre2inch(chiff,0,chchiff);
	chchiff[lgchiff]=0;
	affchaine_2(chchiff,positvid);
	return(lgchiff+positvid);
}

short affchiffre2inch(long chiff,short positch,char *ptrch)
/* position |xx'''''''|*//*or position |-xx''''''|*/
{
	short unite,pass;
	short positchdep;
	int i;
	long testdiz=100000000L;

   positchdep=positch;
	if(chiff<0L){
		chiff=-chiff;
      *(ptrch+positch)='-';
		positch++;
	}
	pass=0;
	for(i=0;i<8;i++){
		if(chiff>=testdiz){
			unite=(short)(chiff/testdiz);
			*(ptrch+positch)=unite+48;
			positch++;
			chiff-=unite*testdiz;
			pass=1;
		}
		else{
			if(pass){
				*(ptrch+positch)=48;
				positch++;
			}
		}
		testdiz/=10L;
	}
	*(ptrch+positch)=chiff+48;
	positch++;
	return(positch-positchdep);
}
"

compile :
gcc  -c testit.c -o testit.o
gcc  -c irq.c -o irq.o
gcc -Wall -x assembler-with-cpp -O0 -mpentium -c irqwrap.s -o
irqwrap.o
gcc -o  calibreu.exe testit.o irq.o  irqwrap.o

irq.c and irq.h are the function found with allegro

gcc version 3.4.1
djgpp version 2.03
Why I have this big jitter? I expected to have 10 us maximum !
especially with a processeur to 1.6 Ghz !
suggestions?