How to get better than 1ms timing resolution

QNX Newsgroups (Archives) qdn.public.qnxrtp.applications
1

We are doing some experiments with QNX where we want to setup a timer to
fire every 600Hz. With the 1 millisecond timing resolution this seems to be
impossible. Even when we simulate a 500Hz process (2 ms), and we have
nothing else running except procnto, the system will occassionally fire a
late pulse (3 ms between pulses).
Is there anyway to improve this besides designing a hardware timer to go on
the bus?

2

“Chris Rose” <chris.rose@viasat.com> wrote in message
news:a21prf$oh3$1@inn.qnx.com…

We are doing some experiments with QNX where we want to setup a timer to
fire every 600Hz. With the 1 millisecond timing resolution this seems to
be
impossible. Even when we simulate a 500Hz process (2 ms), and we have
nothing else running except procnto, the system will occassionally fire a
late pulse (3 ms between pulses).

Is there anyway to improve this besides designing a hardware timer to go
on
the bus?

Increasing priority of process/pulse will help. Also read the 2 timer
articles
on qdn.

Getting 600Hz is a problem since thats 1.66666666 ms. The minimum resolution is 500us. You could try to set the timer resolution via ClockPeriod to 1.666 but Im not sure how out will get round up by the kernel & hardware
resolution.


3

Hi,

this is possible with the Real-Time-Clock (RTC → IRQ8) of your PC.

Below are the setup routines … you have just to write an interrupt
handler for the IRQ8. That interrupt thread should return a pulse which
can trigger your thread every 244us e.g.

Regards

Armin
http://www.steinhoff-automation.com


/*

  • SetupRTC()
    */

void SetupRTC( unsigned short tr )
{
int reg ;

InterruptDisable(); // hopefully no NMIs …
(void) out8( CMOS_ADDR, 0x0A ) ; /* init to read RTC status register A
/
reg = in8( CMOS_DATA ) ; / Read RTC status register A
*/
InterruptEnable();

reg &= CMOS_ADDR; /* save bit 6… bit 4 of status register A */
reg |= tr; /*tr 3 = 122us /
/ 4 = 244us /
/ 5 = 488us /
/ 6 = 976us /
/ 7 =1953us /
/ 8 =3906us */

InterruptDisable();
(void) out8( CMOS_ADDR, 0x0A ); /* init to update RTC status register A
/
(void) out8( CMOS_DATA, reg ) ; / set tick intervall */
InterruptEnable();

InterruptDisable();
(void) out8( CMOS_ADDR, 0x0B ) ;/* init to read register B /
reg = in8( CMOS_DATA ) ; / Read it */
InterruptEnable();

reg |= 0x40 ; /* enable IRQ 8 */

InterruptDisable();
(void) out8( CMOS_ADDR, 0x0B ) ;/* init to update register B /
(void) out8( CMOS_DATA, reg ) ; / Update register B */
InterruptEnable();

/*

  • On some machines there may be dangling interrupts following
  • the POST test. Clear any dangling interrupts here.
    */

InterruptDisable();
(void) out8( CMOS_ADDR, 0x0c ) ;/* Prepare to read register C /
(void) in8( CMOS_DATA ) ; / Read register C to clear interrupts */
InterruptEnable();

}


/*

  • RestoreRTC()
    */

void RestoreRTC( void )
{
int reg ;

InterruptDisable();
(void) out8( CMOS_ADDR, 0x0B ) ;/* init to read register B /
reg = in8( CMOS_DATA ) ; / Read register B */
InterruptEnable();

reg &= 0xBF ; /* Clear interrupt enable bit of IRQ 8*/

InterruptDisable();
(void) out8( CMOS_ADDR, 0x0B ) ;/* init to update register B /
(void) out8( CMOS_DATA, reg ) ;/ Update register B */
InterruptEnable();

InterruptDisable();
(void) out8( CMOS_ADDR, 0x0C ) ;/* init to read register C /
(void) in8( CMOS_DATA ) ; / Read reg. C to clear any interrupts */
InterruptEnable();

}


Chris Rose wrote:

We are doing some experiments with QNX where we want to setup a timer to
fire every 600Hz. With the 1 millisecond timing resolution this seems to be
impossible. Even when we simulate a 500Hz process (2 ms), and we have
nothing else running except procnto, the system will occassionally fire a
late pulse (3 ms between pulses).
Is there anyway to improve this besides designing a hardware timer to go on
the bus?