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From: Ken <>
Subject: timer idioms in embedded system
Date: Thu, 25 Jun 1998 21:10:00 -0000	[thread overview]
Message-ID: <> (raw)

I'm trying to come up with a good timer idiom that doesn't use much
interrupt time.

My current code (single-threaded, no RTOS) uses an array of words to
represent global timers.  The timer interrupt decrements any non-zero
timers. Code that wants to use a timer sets it to a non-zero tick count
and then waits for it to decrement to zero with a simple "while (timer)

I'd like to change this to use a single counter incremented by the
interrupt. Client code would wait for the counter to increment to a
desired value. Example wait code might be

 unsigned long expire_time = clock() + delay;
 while (clock() < expire_time) /* wait */;

How should I handle rollover? I expect the counter to be 32-bit, and the
interrupt tick to be 1 millisecond. The rollover should occur about
every 46 days.

It seems like I could declare the 32-bit values as signed and do
something like

 long clock();
 long expire_time = clock() + delay;
 while ((clock() - expire_time) < 0) /* wait */;

Is this reasonable?

mailto:shiva@CompuServe.COM (Death to Spam!)

             reply	other threads:[~1998-06-25 21:10 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
1998-06-25 21:10 Ken [this message]
     [not found] ` <>
1998-07-03  0:49   ` Ken
1998-06-26  7:13 Dave Hansen

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