5b7d8efa8d
our feet when we look inside timecounter structures. Make the "sync_other" code more robust by never overwriting the tc_next field. Add counters for the bin[up]time functions. Call tc_windup() in tc_init() and switch_timecounter() to make sure we all the fields set right.
103 lines
3.6 KiB
C
103 lines
3.6 KiB
C
/*
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* ----------------------------------------------------------------------------
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* "THE BEER-WARE LICENSE" (Revision 42):
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* <phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you
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* can do whatever you want with this stuff. If we meet some day, and you think
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* this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
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* ----------------------------------------------------------------------------
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*
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* $FreeBSD$
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*/
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#ifndef _SYS_TIMETC_H_
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#define _SYS_TIMETC_H_
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/*
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* Structure used to interface to the machine dependent hardware support
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* for timekeeping.
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*
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* A timecounter is a (hard or soft) binary counter which has two properties:
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* * it runs at a fixed, known frequency.
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* * it must not roll over in less than (1 + delta)/HZ seconds. "delta"
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* is expected to be less than 20 msec, but no hard data has been
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* collected on this. 16 bit at 5 MHz (31 msec) is known to work.
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*
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* get_timecount() reads the counter.
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*
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* counter_mask removes unimplemented bits from the count value.
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*
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* frequency is the counter frequency in hz.
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*
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* name is a short mnemonic name for this counter.
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*
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* cost is a measure of how long time it takes to read the counter.
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*
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* adjustment [PPM << 16] which means that the smallest unit of correction
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* you can apply amounts to 481.5 usec/year.
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*
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* scale_micro [2^32 * usec/tick].
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* scale_nano_i [ns/tick].
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* scale_nano_f [(ns/2^32)/tick].
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*
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* offset_count is the contents of the counter which corresponds to the
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* rest of the offset_* values.
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*
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* offset_sec [s].
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* offset_micro [usec].
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* offset_nano [ns/2^32] is misnamed, the real unit is .23283064365...
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* attoseconds (10E-18) and before you ask: yes, they are in fact
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* called attoseconds, it comes from "atten" for 18 in Danish/Swedish.
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*
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* Each timecounter must supply an array of three timecounters, this is needed
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* to guarantee atomicity in the code. Index zero is used to transport
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* modifications, for instance done with sysctl, into the timecounter being
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* used in a safe way. Such changes may be adopted with a delay of up to 1/HZ,
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* index one & two are used alternately for the actual timekeeping.
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*
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* 'tc_avail' points to the next available (external) timecounter in a
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* circular queue. This is only valid for index 0.
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*
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* `tc_other' points to the next "work" timecounter in a circular queue,
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* i.e., for index i > 0 it points to index 1 + (i - 1) % NTIMECOUNTER.
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* We also use it to point from index 0 to index 1.
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*
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* `tc_tweak' points to index 0.
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*/
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struct timecounter;
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typedef unsigned timecounter_get_t __P((struct timecounter *));
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typedef void timecounter_pps_t __P((struct timecounter *));
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struct timecounter {
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/* These fields must be initialized by the driver. */
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timecounter_get_t *tc_get_timecount;
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timecounter_pps_t *tc_poll_pps;
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unsigned tc_counter_mask;
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u_int32_t tc_frequency;
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char *tc_name;
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void *tc_priv;
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/* These fields will be managed by the generic code. */
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int64_t tc_adjustment;
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u_int64_t tc_scale;
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unsigned tc_offset_count;
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struct bintime tc_offset;
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struct timeval tc_microtime;
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struct timespec tc_nanotime;
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struct timecounter *tc_avail;
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struct timecounter *tc_tweak;
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/* Fields not to be copied in tc_windup start with tc_generation */
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volatile unsigned tc_generation;
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struct timecounter *tc_next;
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};
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#ifdef _KERNEL
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extern struct timecounter *volatile timecounter;
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void tc_init __P((struct timecounter *tc));
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void tc_setclock __P((struct timespec *ts));
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void tc_windup __P((void));
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void tc_update __P((struct timecounter *tc));
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#endif /* !_KERNEL */
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#endif /* !_SYS_TIMETC_H_ */
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