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annotate rtc.h @ 30:435c6330896c

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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
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435c6330896c Set tv_usec in gettimeofday() by using the prescaler counter.
Daniel O'Connor <darius@dons.net.au>
parents:
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1 /* RTC period = RTCCLK/RTC_PR = (32.768 KHz)/(32767+1) */
435c6330896c Set tv_usec in gettimeofday() by using the prescaler counter.
Daniel O'Connor <darius@dons.net.au>
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2 #define RTC_PRESCALE 32768
435c6330896c Set tv_usec in gettimeofday() by using the prescaler counter.
Daniel O'Connor <darius@dons.net.au>
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3
435c6330896c Set tv_usec in gettimeofday() by using the prescaler counter.
Daniel O'Connor <darius@dons.net.au>
parents:
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4 /* usec = x * 1e6 / 32768
435c6330896c Set tv_usec in gettimeofday() by using the prescaler counter.
Daniel O'Connor <darius@dons.net.au>
parents:
diff changeset
5 * However, 1e6 / 32768 = 30.5 which will result in a large error (max of 15807 usec), so we use
435c6330896c Set tv_usec in gettimeofday() by using the prescaler counter.
Daniel O'Connor <darius@dons.net.au>
parents:
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6 * some extra bits to get more precision. We can scale up until 32768 * n is > 2^32.
435c6330896c Set tv_usec in gettimeofday() by using the prescaler counter.
Daniel O'Connor <darius@dons.net.au>
parents:
diff changeset
7 * This results in a maximum error of 1 usec.
435c6330896c Set tv_usec in gettimeofday() by using the prescaler counter.
Daniel O'Connor <darius@dons.net.au>
parents:
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8 */
435c6330896c Set tv_usec in gettimeofday() by using the prescaler counter.
Daniel O'Connor <darius@dons.net.au>
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9 #define RTC_PS2USEC(x) ( \
435c6330896c Set tv_usec in gettimeofday() by using the prescaler counter.
Daniel O'Connor <darius@dons.net.au>
parents:
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10 (uint32_t)( \
435c6330896c Set tv_usec in gettimeofday() by using the prescaler counter.
Daniel O'Connor <darius@dons.net.au>
parents:
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11 (uint32_t)((1 << 9) * (1e6 / RTC_PRESCALE)) * (RTC_PRESCALE - (x))) >> 9)