RE: [avr-gcc-list] 32-bits time

[Loveny Design]

Hi Eric,

It's the TCNT1 rollover you want to avoid, rather than the interrupt. You
could either stop the timer while accessing the register, or simply check
for overflow as follows :-

inline uint32_t timer32_now(void)
{
  uint16_t  tempL, tempH;

  do
  {
    tempL=TCNT1;
    tempH=hiword_time;
  } while (TCNT1 < tempL);

  return (((uint32_t)(tempH)<<16) + tempL);
}

Regards,
Jon


-----Original Message-----
From: address@hidden
[mailto:address@hidden Behalf Of
Eric Pasquier
Sent: Thursday, 13 October 2005 6:22 AM
To: address@hidden
Subject: [avr-gcc-list] 32-bits time


Dear All,

I have implemented a 32-bits time information using the code below.
Timer1 is incremented using internal clock, prescaler=1;
SIG_OVERFLOW interrupt is used to increment a variable used to complete the
16-bits of Timer1.

In fact, the code below have the following problem: if the call is made
exactly when the counter overflow, TCNT1 (tempL) is equal to zero, but
hiword_time (tempH) is pending to be incremented, leading to an error (time
is returning in the past).

Does anybody has a solution ?


I was thinking testing the interrupt flag during the critical section.
Is TCNT1=0 the only case possible ?

Eric.




static uint16_t hiword_time;

//================================================
// timer32_now
// Retrieve the current time from the global clock in Timer1,
// disabling interrupts to avoid stomping on the TEMP register.
//------------------------------------------------
inline uint32_t timer32_now(void)
{
  int8_t    sreg;
  uint16_t  tempL, tempH;

  sreg=SREG;
  cli();
  tempL=TCNT1;
  tempH=hiword_time;
  SREG=sreg;

  return (((uint32_t)(tempH)<<16) + tempL);
}

//================================================
// SIG_OVERFLOW1
//------------------------------------------------
SIGNAL( SIG_OVERFLOW1 )
{
  hiword_time++;
}