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2009-03-02 Till Straumann <strauman@slac.stanford.edu>

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PR 1375/bsps
	* clock/clock.c: Correct implementation of nanoseconds since last tick
	handler.
This commit is contained in:
Joel Sherrill
2009-03-02 18:57:20 +00:00
parent 73d1f0799f
commit cb54e10686
2 changed files with 64 additions and 5 deletions
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6
c/src/lib/libbsp/m68k/uC5282/ChangeLog
View File

@@ -1,3 +1,9 @@
2009-03-02 Till Straumann <strauman@slac.stanford.edu>
PR 1375/bsps
* clock/clock.c: Correct implementation of nanoseconds since last tick
handler.
2009-01-21 Eric Norum <norume@aps.anl.gov>
PR 1358/bsps

63
c/src/lib/libbsp/m68k/uC5282/clock/clock.c
View File

@@ -35,13 +35,66 @@ extern int __SRAMBASE[];
uint32_t bsp_clock_nanoseconds_since_last_tick(void)
{
int i = MCF5282_PIT3_PCNTR;
if (MCF5282_PIT3_PCSR & MCF5282_PIT_PCSR_PIF)
i = MCF5282_PIT3_PCNTR - USEC_PER_TICK;
return (USEC_PER_TICK - i) * 1000;
uint32_t tdiff;
/* Details to consider here:
*
* - PIT is 16-bit. To properly handle differences of two
* 16-bit numbers (which requires 17-bits) we want to
* do the arithmetic in a wider data type. PIT reading
* is a unsigned 16-bit count.
*
* => must make sure PIT is a *unsigned* 16-bit type. Otherwise
* values get sign-extended when converted to wider type
* (regardless of the signedness of wider type):
*
* (unsigned)(signed short)0xffff -> 0xffffffff.
*
* and thus
*
* (uint32_t)(int16_t)65535 - (uin32_t)(int16_t)1
*
* would yield 0xfffffffe, not 65534!
*
*
* - PIT counts backwards from PMR -> zero, hence
*
* now - tick_base = (PMR - now) - (PMR - tick_base) = tick_base - now;
*
* result may be negative (if rolled-over).
*
* - PIF flag, counter and PCNTR_AT_TICK must all
* be read atomically - otherwise an interrupt may
* have altered their values while we're looking.
*
* NOTE: score framework calling this routine disables
* interrupts during execution of this callout.
*
* - Last but not least, rollover might have happened
* just between reading counter and PIF flag; hence
* we have to re-read the counter if PIF is set.
*
*/
/* obtain current value */
tdiff = (uint16_t)MCF5282_PIT3_PCNTR;
if (MCF5282_PIT3_PCSR & MCF5282_PIT_PCSR_PIF) {
/* rollover may just have happened;
* must reload PCNTR.
*/
tdiff = + (uint32_t)(uint16_t)MCF5282_PIT3_PMR
+ (uint32_t)(uint16_t)PCNTR_AT_TICK
- (uint32_t)(uint16_t)MCF5282_PIT3_PCNTR;
} else {
tdiff = + (uint32_t)(uint16_t)PCNTR_AT_TICK - tdiff;
}
return tdiff * 1000;
}
#define Clock_driver_nanoseconds_since_last_tick bsp_clock_nanoseconds_since_last_tick
#define Clock_driver_nanoseconds_since_last_tick \
bsp_clock_nanoseconds_since_last_tick
/*
* Periodic interval timer interrupt handler