int32_t last_seqno = -1;
uint8_t packet[2048], *pktp;
- uint64_t time_of_previous_packet_fp = 0;
+ uint64_t time_of_previous_packet_ns = 0;
float longest_packet_time_interval_us = 0.0;
// mean and variance calculations from "online_variance" algorithm at
frame_count++;
- uint64_t local_time_now_fp = get_absolute_time_in_fp();
- if (time_of_previous_packet_fp) {
+ uint64_t local_time_now_ns = get_absolute_time_in_ns();
+ if (time_of_previous_packet_ns) {
float time_interval_us =
- (((local_time_now_fp - time_of_previous_packet_fp) * 1000000) >> 32) * 1.0;
- time_of_previous_packet_fp = local_time_now_fp;
+ (local_time_now_ns - time_of_previous_packet_ns) * 0.001;
+ time_of_previous_packet_ns = local_time_now_ns;
if (time_interval_us > longest_packet_time_interval_us)
longest_packet_time_interval_us = time_interval_us;
stat_n += 1;
stat_n = 0;
stat_mean = 0.0;
stat_M2 = 0.0;
- time_of_previous_packet_fp = 0;
+ time_of_previous_packet_ns = 0;
longest_packet_time_interval_us = 0.0;
}
} else {
- time_of_previous_packet_fp = local_time_now_fp;
+ time_of_previous_packet_ns = local_time_now_ns;
}
if (nread >= 0) {
obfp += 2;
};
*obfp = 0;
-
-
+
+
// get raw timestamp information
// I think that a good way to understand these timestamps is that
// (1) the rtlt below is the timestamp of the frame that should be playing at the
// Thus, (3) the latency can be calculated by subtracting the second from the
// first.
// There must be more to it -- there something missing.
-
+
// In addition, it seems that if the value of the short represented by the second
// pair of bytes in the packet is 7
// then an extra time lag is expected to be added, presumably by
// the AirPort Express.
-
+
// Best guess is that this delay is 11,025 frames.
-
+
uint32_t rtlt = nctohl(&packet[4]); // raw timestamp less latency
uint32_t rt = nctohl(&packet[16]); // raw timestamp
-
+
uint32_t fl = nctohs(&packet[2]); //
-
+
debug(1,"Sync Packet of %d bytes received: \"%s\", flags: %d, timestamps %u and %u,
giving a latency of %d frames.",plen,obf,fl,rt,rtlt,rt-rtlt);
//debug(1,"Monotonic timestamps are: %" PRId64 " and %" PRId64 "