Mercurial > ~darius > hgwebdir.cgi > stm32temp

view rtc.h @ 30:435c6330896c

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Set tv_usec in gettimeofday() by using the prescaler counter.
author Daniel O'Connor <darius@dons.net.au>
date Tue, 27 Nov 2012 13:19:11 +1030
parents
children
line wrap: on
line source

/* RTC period = RTCCLK/RTC_PR = (32.768 KHz)/(32767+1) */
#define RTC_PRESCALE 32768

/* usec = x * 1e6 / 32768
 * However, 1e6 / 32768 = 30.5 which will result in a large error (max of 15807 usec), so we use
 * some extra bits to get more precision. We can scale up until 32768 * n is > 2^32.
 * This results in a maximum error of 1 usec.
 */
#define RTC_PS2USEC(x) ( \
	(uint32_t)( \
	    (uint32_t)((1 << 9) * (1e6 / RTC_PRESCALE)) * (RTC_PRESCALE - (x))) >> 9)