Mercurial > ~darius > hgwebdir.cgi > stm32temp
comparison rtc.h @ 30:435c6330896c
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 |
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| 29:077cdff4662a | 30:435c6330896c |
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| 1 /* RTC period = RTCCLK/RTC_PR = (32.768 KHz)/(32767+1) */ | |
| 2 #define RTC_PRESCALE 32768 | |
| 3 | |
| 4 /* usec = x * 1e6 / 32768 | |
| 5 * However, 1e6 / 32768 = 30.5 which will result in a large error (max of 15807 usec), so we use | |
| 6 * some extra bits to get more precision. We can scale up until 32768 * n is > 2^32. | |
| 7 * This results in a maximum error of 1 usec. | |
| 8 */ | |
| 9 #define RTC_PS2USEC(x) ( \ | |
| 10 (uint32_t)( \ | |
| 11 (uint32_t)((1 << 9) * (1e6 / RTC_PRESCALE)) * (RTC_PRESCALE - (x))) >> 9) |