From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Hansen To: shiva@compuserve.com, c++-embedded@cygnus.com, shiva@well.com Subject: Re: timer idioms in embedded system Date: Fri, 26 Jun 1998 07:13:00 -0000 Message-id: X-SW-Source: 1998/msg00010.html If you stay in unsigned integer math, you can pretty much ignore rollover. Signed math may bite you since it's not as well defined. Change your client code to work something like: unsigned long start = clock(); while ((clock()-start) < delay) wait(); For example, if start==0xFFFFFFF0 and clock() returns 4, the result of the subtraction will be 4 - 0xFFFFFFF0 or 0x00000014 HTH. Regards, -=Dave >>> Ken 06/25/98 10:41PM >>> 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? -- Ken mailto:shiva@well.com mailto:shiva@CompuServe.COM http://www.well.com/user/shiva/ http://sewnsurf.home.ml.org/ http://www.e-scrub.com/cgi-bin/wpoison/wpoison.cgi (Death to Spam!) ! !