Jetson Orgin AGX camera frames time sync

Robotics & Edge Computing Jetson & Embedded Systems Jetson AGX Orin
1

Hello,

I am working on a project with a number of different sensors connected to a Jetson Orin AGX and I really want to have them all provide timestamps synced to the same time domain.

The issue I have is that seems like tegra camera system via Argus provides video frames with TSC monotonic timestamps and all our other systems (like lidars) provide timestams synced via PTP to a Linux Realtime time domain.

So, I am looking for a way to somehow synchronize timestamps I get from cameras to a real time Linux clock. As far as I use Jetpack 6.2 I have found this code snippet somewhere on this forum:

uint64_t readOffsetNs() {
  unsigned long raw_nsec, tsc_ns;
  unsigned long cycles, frq;
  struct timespec tp;

  asm volatile("mrs %0, cntfrq_el0" : "=r"(frq));
  asm volatile("mrs %0, cntvct_el0" : "=r"(cycles));

  clock_gettime(CLOCK_MONOTONIC, &tp);

  tsc_ns = (cycles * 100 / (frq / 10000)) * 1000;
  raw_nsec = tp.tv_sec * 1000000000 + tp.tv_nsec;

  printf("offset_ns:%lld\n", llabs(tsc_ns - raw_nsec));

  return 0;
}

int main(void) {
  //   for (int i = 0; i < 1000; i++) {
  for (;;) {
    sleep(1);
    readOffsetNs();
  }
}

However, my results do not look promising with CLOCK_MONOTONIC and even worse when I try to use CLOCK_REALTIME

offset_ns:31399060681
offset_ns:31399014118
.........
offset_ns:31398545276
offset_ns:31398551299
offset_ns:31398557130
offset_ns:31398562665

Are there any actual ways to get all my sensors synchronized and use one clock domain, or the only possible way to use this calculated offset with more than 1ms jitter?

5

This is the only way for current design.

BTW, your sensor HW need sync design first.

6

Thank you for your reply, could you please provide me more details about what you mean by “HW need sync design first”? Is it like an external trigger for lidars/cameras etc?

7

Yes, need external trigger to make sure the sensors output data in sync mode.

8

BTW, is it possible to sync TSCs on two Orins or only use external sync signal?

9

No way to sync the TSC but system time by NTP.

Thanks

11

Thanks for your reply.
I have just noticed an interesting behavior I can not explain:
I have two Orin AGX with 6.2 jetpack and when I run the program I attached previously on one of the Orins I get an offset deviation is only about 1-2us
However the same measurement on the second Orin gives me >100ms deviation.
I actually could not find an issue or any difference between this Orins, could you please give me a clue what might be going on here?

12

And one more question after I carefuly read this topic one more time.
Did I get right, now I can use Argus::ICaptureMetadata::getSensorTimestamp to get a CLOCK_MONOTONIC_RAW frame timestamp and I shouldn’t use and additional calculations from TSC HW time to linux system monotonic time?
Does Argus make this conversion by itself?

13

You need conversion by yourself.

14

Here is what I do:

  1. Customize nvarguscamerasrc by adding auto ts = iMetadata->getSensorTimestamp(); to StreamConsumer::threadExecute. So as far as I understand ts here is a TSC Hardware timestamp.
  2. Get current TSC HW timestamp via reading cntfrq_el0 and cntvct_el0 regs as it was shown in the referenced post.
  3. Calculate the difference between current timestamp and ts and get a value ~31s

If iMetadata->getSensorTimestamp() provides TSC HW timestamps the difference between it and the current TSC HW time must be much less and equals about 20ms I guess.

However, when I make the same experiment but now I obtain current timestamp via clock_gettime(CLOCK_MONOTONIC_RAW, &real) the difference is about 20ms what makes me think that getSensorTimestamp() actually provides Linux Kernel CLOCK_MONOTONIC_RAW time.

Could you please clarify this for me. I use 6.2 Jetpack btw

15

Could you confirm by SOF.

16

Yep confirmed, it gives real TSC time, however I still wonder, why it doesn’t work with getSensorTimestamp

17

Looks like the getSensorTimestamp is CLOCK_MONOTONIC time.

18

Do you know when it obtains?

19

getSensorTimestamp()
virtual uint64_t Argus::ICaptureMetadata::getSensorTimestamp ( ) const
pure virtual

Returns the start timestamp for the sensor (in nanoseconds).

This is the time that the first data from this capture arrives from the sensor.

20

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