Improve stability of PHC reading in phc2sys.
Make five PHC readings in sequence and pick the quickest one. Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>master
parent
2fcf5cbb4f
commit
d42914c335
29
phc2sys.c
29
phc2sys.c
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@ -41,6 +41,8 @@
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#define max_ppb 512000
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#define min_ppb -512000
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#define PHC_READINGS 5
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static clockid_t clock_open(char *device)
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{
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int fd = open(device, O_RDWR);
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@ -87,25 +89,34 @@ static void clock_step(clockid_t clkid, int64_t ns)
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static int read_phc(clockid_t clkid, clockid_t sysclk, int rdelay, int64_t *offset, uint64_t *ts)
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{
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struct timespec tsrc, tdst;
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struct timespec tdst1, tdst2, tsrc;
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int i;
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int64_t interval, best_interval = INT64_MAX;
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if (clkid == CLOCK_INVALID) {
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return 0;
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}
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if (clock_gettime(clkid, &tsrc)) {
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/* Pick the quickest clkid reading. */
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for (i = 0; i < PHC_READINGS; i++) {
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if (clock_gettime(sysclk, &tdst1) ||
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clock_gettime(clkid, &tsrc) ||
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clock_gettime(sysclk, &tdst2)) {
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perror("clock_gettime");
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return 0;
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}
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if (clock_gettime(sysclk, &tdst)) {
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perror("clock_gettime");
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return 0;
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}
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interval = (tdst2.tv_sec - tdst1.tv_sec) * NS_PER_SEC +
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tdst2.tv_nsec - tdst1.tv_nsec;
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*offset = tdst.tv_sec * NS_PER_SEC - tsrc.tv_sec * NS_PER_SEC +
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tdst.tv_nsec - tsrc.tv_nsec - rdelay;
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*ts = tdst.tv_sec * NS_PER_SEC + tdst.tv_nsec;
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if (best_interval > interval) {
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best_interval = interval;
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*offset = (tdst1.tv_sec - tsrc.tv_sec) * NS_PER_SEC +
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tdst1.tv_nsec - tsrc.tv_nsec +
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interval / 2 - rdelay;
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*ts = tdst2.tv_sec * NS_PER_SEC + tdst2.tv_nsec;
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}
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}
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return 1;
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}
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