From: jeffkhc AT netvigator DOT com (jeffchan)
Newsgroups: comp.os.msdos.programmer,comp.os.msdos,comp.os.msdos.djgpp,comp.os.msdos.misc
Subject: Re: Control timing
Date: 26 Oct 2001 01:54:19 -0700
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To: djgpp AT delorie DOT com
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Thanks your kindly information.

I use this code and having modification to verify the performance when
i make it faster.

My testing is checking the reading of x after certain time.
For 1kHz, that's okay. For 8kHz, the result is the same as 1kHz.

What's the problem?

/**************************************/
#include	<stdio.h>
#include	<stdlib.h>
#include	<dos.h>
#include	<bios.h>
/******************function prototype*******************************/
void init_timer(void);
void deinit_timer(void);
static void interrupt new_timer(void);
/*******************************main********************************/
unsigned long x=0;
int main(){
	init_timer();
	while( !bioskey(1) ){
	}
	deinit_timer();
        printf("\n%ld", x);
	return 0;
}
/**************************************************************/
/* ---------------------- new_timer() -------------------*/
static void interrupt new_timer(void){
    asm cli
    x++;
    // reset PIC
    asm {
	mov al, 20h
        out 20h, al
    } 
   asm sti
}
/*********************************************************************/
/* ---------------------- init_timer() ------------------ */
void init_timer(void){
	oldtimer=getvect(8);			// save old timer
	asm cli
	// speed up clock
	asm {					
		mov	bx, 149   //set the clock to 8kHz
                                  //1193180/8kHz=149
		mov     al, 00110110b
		out     43h,al
		mov     al, bl
		out     40h, al
    	        mov     al, bh
		out     40h, al
	}
    setvect(8, new_timer);
	asm sti
}
/* ---------------------- deinit_timer() ---------------- */
void deinit_timer(void){
	asm cli
	// slow down clock   1193180 / 65536 = 18.2, but we use zero
	asm {
	    xor	 bx, bx          // min rate 18.2 Hz when set to zero
    	    mov	 al, 00110110b
	    out  43h, al
	    mov	 al, bl
    	    out  40h, al
	    mov  al, bh
	    out  40h, al
        }
	setvect(8, oldtimer);  // restore oldtimer
	asm sti
}

 



"Alexander Russell" <alexander DOT russell AT telus DOT com> wrote in message news:<B9NB7.30940$%K4 DOT 5763583 AT news1 DOT telusplanet DOT net>...
> "jeffchan" <jeffkhc AT netvigator DOT com> wrote in message
> news:bf50ce95 DOT 0110242053 DOT 1568dcea AT posting DOT google DOT com...
> > Hi,
> >
> > now an external data is fed into a capture card and i need store the
> > captured data into hard drive. The capture card is controlled under
> > msdos and my control program is written by turbo c.
> >
> > The sampling rate is expected around 8kHz per channel. Now i want to
> > create 8, 16 or 32 channels. Polling method with looping delay to each
> > channel i use in currently because the card can't capture different
> > channels at the same time.
> >
> > However, i find that the timing is difficult to control.
> >
> > Any suggestion or improvement advice?
> >
> > Is using timer interrept possible? If yes, any information about it,
> > such as interrupt number, or how fast of that timer, etc.?
> > (Actually i find that int 0x1C isn't fast enough to do that, only
> > 18.25Hz)
> >
> > Jeff
> 
> You can reprogram the timer to run faster. A sample is in common.zip at
> http://www3.telus.net/alexander_russell
> see timer.c, speed up the timer, and install a simple ISR
> 
> The faq for comp.os.msdos.programmer (use google or get from the group) has
> good information on timing under DOS.