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Added a clock_seconds() function prototype to core/sys/clock.h, that returns seconds in 32 bit format. On platforms like the MSP430, which has a 16 bit native datatype, this cannot be implemented with an interrupt tick that increments a 32 bit value because access is not atomic. Instead, the MSP430 code increments 16 bit seconds value and converts this into a 32 bit value through an offset calculation. If the new value is smaller than the last check, the offset is incremented by 65536. This change also means that CLOCK_CONF_SECOND must be a power of two because a modulo operation is used inside the periodic tick interrupt handler.

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This commit is contained in:
adamdunkels 2008-07-07 23:38:09 +00:00
parent ba5c18a468
commit fc6d059d24
1 changed files with 33 additions and 4 deletions
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37
cpu/msp430/clock.c
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@ -28,7 +28,7 @@
*
* This file is part of the Contiki operating system.
*
* @(#)$Id: clock.c,v 1.13 2008/07/03 23:59:20 adamdunkels Exp $
* @(#)$Id: clock.c,v 1.14 2008/07/07 23:38:09 adamdunkels Exp $
*/
@ -47,6 +47,8 @@
#define MAX_TICKS (~((clock_time_t)0) / 2)
static volatile unsigned short seconds;
static volatile clock_time_t count = 0;
/* last_tar is used for calculating clock_fine, last_ccr might be better? */
static unsigned short last_tar = 0;
@ -58,12 +60,24 @@ interrupt(TIMERA1_VECTOR) timera1 (void) {
do {
TACCR1 += INTERVAL;
++count;
/* Make sure the CLOCK_CONF_SECOND is a power of two, to ensure
that the modulo operation below becomes a logical and and not
an expensive divide. Algorithm from Wikipedia:
http://en.wikipedia.org/wiki/Power_of_two */
#if (CLOCK_CONF_SECOND & (CLOCK_CONF_SECOND - 1)) != 0
#error CLOCK_CONF_SECOND must be a power of two (i.e., 1, 2, 4, 8, 16, 32, 64, ...).
#error Change CLOCK_CONF_SECOND in contiki-conf.h.
#endif
if(count % CLOCK_CONF_SECOND == 0) {
++seconds;
}
} while((TACCR1 - TAR) > INTERVAL);
last_tar = TAR;
if(etimer_pending()
&& (etimer_next_expiration_time() - count - 1) > MAX_TICKS) {
if(etimer_pending() &&
(etimer_next_expiration_time() - count - 1) > MAX_TICKS) {
etimer_request_poll();
LPM4_EXIT;
}
@ -170,7 +184,22 @@ clock_set_seconds(unsigned long sec)
unsigned long
clock_seconds(void)
{
return count / CLOCK_SECOND;
static unsigned long offset;
static unsigned long last_time;
unsigned long new_time;
new_time = seconds + offset;
/* printf("Seconds %d new_time %lu offset %lu\n", seconds, new_time, offset);*/
if(new_time < last_time) {
offset += 0x10000L;
new_time += 0x10000L;
}
last_time = new_time;
return new_time;
}
/*---------------------------------------------------------------------------*/
rtimer_clock_t