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  • ddrown's Avatar
    08-02-2020, 04:23 AM
    My two have a tempco of 0.154ppm/C and 0.206ppm/C, so that fits with your 0.195ppm/C. Wander being 0.005 ppm in an hour is pretty impressive.
    29 replies | 1258 view(s)
  • ddrown's Avatar
    07-31-2020, 03:51 AM
    Nice! Good idea with the cinderblock, that should add a lot of thermal mass
    29 replies | 1258 view(s)
  • ddrown's Avatar
    07-30-2020, 06:02 AM
    I'm curious why you assume the frequency changes are coming from the GPSDO and not from the Teensy's crystal. Could you explain why you suspect the one but not the other?
    29 replies | 1258 view(s)
  • ddrown's Avatar
    07-30-2020, 05:03 AM
    chisquare values are in counts (25MHz) so 42.9 counts = 1.7us. Those values look reasonable to me. I'm considering dropping old samples when the chisq value is high. This usually happens when the local clock is...
    29 replies | 1258 view(s)
  • ddrown's Avatar
    07-29-2020, 02:28 AM
    This code is only built as an NTP (not PTP) server. But I do have different code for the esp8266: https://github.com/ddrown/esp8266-clock It uses an NTP client to keep the local clock in sync, and displays the time...
    29 replies | 1258 view(s)
  • ddrown's Avatar
    07-24-2020, 03:08 AM
    I let this run for 5 days, and these are interesting results. I have two different Teensy 4.1 boards running this code. Temperature vs frequency over 256 second intervals: Just using a linear fit gives a...
    29 replies | 1258 view(s)
  • ddrown's Avatar
    07-19-2020, 03:33 AM
    I've added this line to updateTime: Serial.printf("PPS: %u %u %.2f\r\n", gpstime, lastPPS, tempmonGetTemp()); I've collected this type of data in the past for other crystals, so I'd like to redo the plots below for...
    29 replies | 1258 view(s)
  • ddrown's Avatar
    07-18-2020, 08:12 PM
    That looks good, thanks for trying it out!
    29 replies | 1258 view(s)
  • ddrown's Avatar
    07-17-2020, 06:06 AM
    Sure, the short term phase noise from the crystal will be much lower than the GPS. But I think what is causing the larger offsets are the frequency change due to temperature changes. It would be worth testing covering...
    29 replies | 1258 view(s)
  • ddrown's Avatar
    07-17-2020, 02:35 AM
    The phase offsets happen at the same time as the frequency changes, which has me thinking that my synchronization code needs some tweaking. I suspect PPS from a GPSDO wouldn't change much unless the system clock also...
    29 replies | 1258 view(s)
  • ddrown's Avatar
    07-04-2020, 09:21 PM
    The RMC message taking more than 1s would generate those lag error messages. The LAG messages can also be caused by no pps due to signal lock loss. I'm surprised you're getting B (bad time) though. Is your GPS...
    29 replies | 1258 view(s)
  • ddrown's Avatar
    07-04-2020, 09:19 PM
    Yes, I'm using the firmware defaults for the adafruit GPS, which is 9600 and no ZDA message. I'm also using an external antenna on a windowsill. Without an external antenna, I get bad reception. Yeah, 300ms ish...
    29 replies | 1258 view(s)
  • ddrown's Avatar
    07-04-2020, 08:15 PM
    I setup a second teensy with an Adafruit GPS. I added the GPS_USES_RMC define to settings.h to support it. Originally I took the timestamp of the GPRMC message, but it would often be delayed into the next second,...
    29 replies | 1258 view(s)
  • ddrown's Avatar
    07-02-2020, 05:09 PM
    The columns from that output: T41 raw counter value at PPS (25MHz) seconds offset between GPS PPS and virtual T41 clock (which is the first graph). The third graph is the measurement over the network, which will...
    29 replies | 1258 view(s)
  • ddrown's Avatar
    06-30-2020, 11:09 PM
    I wanted to use the teensy_loader_cli but the soft reboot option wasn't working for me. I didn't dig very far into why it wasn't working, but I put together a workaround. If you send the character "r" to the serial,...
    29 replies | 1258 view(s)
  • ddrown's Avatar
    06-28-2020, 04:15 AM
    I ported the embedded NTP stratum 1 server that I originally wrote for the stm32f407. It uses the 1588 ethernet hardware for RX and TX timestamps. I'm also using the 1588 event input capture to measure the reference...
    29 replies | 1258 view(s)
  • ddrown's Avatar
    06-26-2020, 12:43 AM
    I went the osh park + digikey route to get an Ethernet connector for the Teensy 4.1, and I can report that it does work that way :) After getting the lwip_iperf example working, I had to tune lwip for maximum...
    0 replies | 129 view(s)
  • ddrown's Avatar
    06-25-2020, 02:08 PM
    Looks good, thank you!
    3 replies | 275 view(s)
  • ddrown's Avatar
    06-24-2020, 05:57 AM
    I just noticed this too. D2 is EMC_25 and D1 is EMC_28, which are also on the schematic.
    3 replies | 275 view(s)
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