GPS Module: Difference between revisions

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PPS can be reconfigured as a frequency reference:
PPS:
* Send PPS to UART via CTS
* Send PPS to UART via CTS to allow GPSD to acurately sync
* 0.25 Hz - 10 MHz
* Can be configured as a frequency reference: 0.25 Hz - 10 MHz
** Output has high frequency accuracy
** Suffers from jitter except at a few specific frequencies that divide into internal 48 MHz clock
* Configure in u-Center [[Media:u-Center Configuration.png|here]]
* Configure in u-Center [[Media:u-Center Configuration.png|here]]
* Output has high frequency accuracy, but suffers from jitter except at a few specific frequencies
* Different frquencies/duty cycles can be configure for GPS synced/not synced


== Software ==
== Software ==
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* Communicates with uBlox with binary UBX Protocol
* Communicates with uBlox with binary UBX Protocol


View/Change Settings (View -> Configuration View), Send to activate change:
View -> Configuration View; to activate change: Send
* CFG (Configuration)
** Select: Save current configuration
** Select in Devices: 2-I2C-EEPROM
* PRT (Ports)
* PRT (Ports)
** Baud Rate : 9600 -> 115200
** Baud Rate : 9600 -> 115200
* TP5 (Timepulse 5)
* TP5 (Timepulse 5)
** Frequency : 1 Hz -> 10 Hz
** PPS Settings for no GPS lock (eg use as an "alert" signal):
** Duty Cycle : 100% -> 25%
*** Frequency : 1 Hz
** Frequency Locked : 1 Hz
*** Duty Cycle : 0% (for permanent low output)
** Duty Locked : 50%
** PPS Settings for GPS Locked:
** Rising Edge on TOS
*** Frequency Locked : 1 Hz
** Cable Delay : 50 ns -> 10 ns (compensates for cable delay between antenna and reciver)
*** Duty Locked : 50%
** UBX -> CFG (Config) -> CFG (Configuration) [Save accross reboots]
** Falling Edge on TOS
** Select 2-I2C-EEPROM in the Devices option
** Cable Delay : 50 ns -> 20 ns (This compensates for cable delay between antenna and receiver)
*** At 0.7c, 1 m <=> 4.8 ns


Save accross reboots (view -> Message View):
View -> Message View:
* Firmware version: UBX -> MON (Monitor) -> VER (Version)
* Firmware version: UBX -> MON (Monitor) -> VER (Version)
** Currently: 7.03 (45969)


=== GPSD ===
=== GPSD ===
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Can be tested with something like (Debug level 4) :
Can be tested with something like (Debug level 4) :
  gpsd -N -n -s 9600 -D 4 /dev/ttyS0 /dev/pps0
  gpsd -N -n -s 9600 -D 4 /dev/ttyS0 /dev/pps0
Lines showing visible/used satellites:
gpsd:PROG: SVINFO: visible=15 used=5 mask={SATELLITE|USED}
gpsd:INFO: CORE: PRN  6 az  47.0 el 20.0 ( 0.687248,  0.640869,  0.342020)
gpsd:INFO: CORE: PRN  11 az  93.0 el 22.0 ( 0.925913, -0.048525,  0.374607)
gpsd:INFO: CORE: PRN  12 az  70.0 el 58.0 ( 0.497961,  0.181243,  0.848048)
gpsd:INFO: CORE: PRN  28 az 301.0 el 35.0 (-0.702150,  0.421894,  0.573576)
gpsd:INFO: CORE: PRN  32 az 257.0 el 44.0 (-0.700903, -0.161816,  0.694658)
gpsd:INFO: CORE: Sats used (5):
Line showing time in [https://www.epochconverter.com/clock UNIX Epoch]:
gpsd:PROG: TIMEGPS: time= 1728071281.000150311 mask={TIME}
Line showing PPS is asserted on control line. Here the control line is asserted with 0.5s delay:
gpsd:PROG: PPS:/dev/ttyUSB0 Assert accepted @  1728071281.503229046 offset  0.496770954


Configuration in /etc/sysconfig/gpsd, which by default enables detection of USB devices via udev events including creation of a PPS device (/dev/pps0):
Configuration in /etc/sysconfig/gpsd, which by default enables detection of USB devices via udev events including creation of a PPS device (/dev/pps0):
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  gpsmon
  gpsmon


Can show raw data:
Show raw data:
  gpscat /dev/ttyS0
  gpscat -p -s 9600 /dev/ttyS0


Enable and start gpsd:
Enable and start gpsd:
  systemctl enable gpsd
  systemctl enable gpsd
  systemctl start gpsd
  systemctl start gpsd
By default, gpsd listens on port 2947.


Monitor with:
Monitor with:
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Check PPS signal:
Check PPS signal:
  ppstest /dev/pps0
  # ppstest /dev/pps0
  ppscheck /dev/ttyS0
  trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1733262552.000005797, sequence: 308579 - clear  1733262552.499996498, sequence: 308580
source 0 - assert 1733262553.000004664, sequence: 308580 - clear  1733262552.499996498, sequence: 308580
source 0 - assert 1733262553.000004664, sequence: 308580 - clear  1733262553.500003597, sequence: 308581
source 0 - assert 1733262554.000004920, sequence: 308581 - clear  1733262553.500003597, sequence: 308581
source 0 - assert 1733262554.000004920, sequence: 308581 - clear  1733262554.500000766, sequence: 308582
 
# ppscheck /dev/ttyS0
...
  KPPS  1733262666.000002906    assert  308693
  KPPS  1733262665.500002983    clear  308693
 
  KPPS  1733262666.499814138    clear  308694
  KPPS  1733262666.999988850    assert  308694
 
ppscheck /dev/ttyS0


Can set at boot with udev rule (/etc/udev/rules.d/gps.rules):
Can set at boot with udev rule (/etc/udev/rules.d/gps.rules):

Latest revision as of 21:53, 3 December 2024

HW-595 Board

uBlox GPS Board
  • Based on uBlox NEO-6M-0-001
  • Receiver Description
  • 5V operation (3.3 V regulator onboard)
  • UART: 4800 - 230400 bps (9600 bps 8N1 default), TTL levels buffered by 220R resistors
  • U.FL connector supplies 3.3 V to active antenna
  • Crystal Osc, not TCXO
  • PPS LED: Invertion of PPS pin
  • Battery-backed RAM contains config data and clock and speeds first-time-to-fix
  • Data in NMEA 0183 format
  • More background here

Board pinouts:

Pin Function Description
1 PPS 1 pulse/s, synchronised at rising edge, length 100 ms (by default)
2 RXD UART input
3 TXD UART output
4 GND Ground
5 VCC 3.3 - 5 V

PPS:

  • Send PPS to UART via CTS to allow GPSD to acurately sync
  • Can be configured as a frequency reference: 0.25 Hz - 10 MHz
    • Output has high frequency accuracy
    • Suffers from jitter except at a few specific frequencies that divide into internal 48 MHz clock
  • Configure in u-Center here
  • Different frquencies/duty cycles can be configure for GPS synced/not synced

Software

U-Center

  • U-Center
  • Select COM port and Baud rate
  • Communicates with uBlox with binary UBX Protocol

View -> Configuration View; to activate change: Send

  • CFG (Configuration)
    • Select: Save current configuration
    • Select in Devices: 2-I2C-EEPROM
  • PRT (Ports)
    • Baud Rate : 9600 -> 115200
  • TP5 (Timepulse 5)
    • PPS Settings for no GPS lock (eg use as an "alert" signal):
      • Frequency : 1 Hz
      • Duty Cycle : 0% (for permanent low output)
    • PPS Settings for GPS Locked:
      • Frequency Locked : 1 Hz
      • Duty Locked : 50%
    • Falling Edge on TOS
    • Cable Delay : 50 ns -> 20 ns (This compensates for cable delay between antenna and receiver)
      • At 0.7c, 1 m <=> 4.8 ns

View -> Message View:

  • Firmware version: UBX -> MON (Monitor) -> VER (Version)
    • Currently: 7.03 (45969)

GPSD

  • gpsd
  • Packages: gpsd, gpsd-clients

Use of a serial device (eg ttyS0) is prefered over a USB/serial interface (eg ttyUSB0) due to lower latency and PPS availability.

Can be tested with something like (Debug level 4) : 

gpsd -N -n -s 9600 -D 4 /dev/ttyS0 /dev/pps0

Lines showing visible/used satellites: 

gpsd:PROG: SVINFO: visible=15 used=5 mask={SATELLITE|USED}
gpsd:INFO: CORE: PRN   6 az  47.0 el 20.0 ( 0.687248,  0.640869,  0.342020)
gpsd:INFO: CORE: PRN  11 az  93.0 el 22.0 ( 0.925913, -0.048525,  0.374607)
gpsd:INFO: CORE: PRN  12 az  70.0 el 58.0 ( 0.497961,  0.181243,  0.848048)
gpsd:INFO: CORE: PRN  28 az 301.0 el 35.0 (-0.702150,  0.421894,  0.573576)
gpsd:INFO: CORE: PRN  32 az 257.0 el 44.0 (-0.700903, -0.161816,  0.694658)
gpsd:INFO: CORE: Sats used (5):

Line showing time in UNIX Epoch: gpsd:PROG: TIMEGPS: time= 1728071281.000150311 mask={TIME}

Line showing PPS is asserted on control line. Here the control line is asserted with 0.5s delay: 

gpsd:PROG: PPS:/dev/ttyUSB0 Assert accepted @  1728071281.503229046 offset  0.496770954

Configuration in /etc/sysconfig/gpsd, which by default enables detection of USB devices via udev events including creation of a PPS device (/dev/pps0): 

USBAUTO="true"

Options can be forced, eg: 

OPTIONS="-n -s 9600"
DEVICES="/dev/ttyS0 /dev/pps0"

Check data stream with gpsmon: 

gpsmon /dev/ttyS0

when gpsd is not started, or connected to gpsd: 

gpsmon

Show raw data: 

gpscat -p -s 9600 /dev/ttyS0

Enable and start gpsd: 

systemctl enable gpsd
systemctl start gpsd

By default, gpsd listens on port 2947.

Monitor with: 

cgps -s
gpsmon
gpscsv
gpsplot --image gps.png
xgps

Pulse Per Second (PPS)

With PPS output connected to a serial port pin, GPSD should detect it. If it is on GPIO or other serial port, this can be used to create a PPS device: 

dnf install pps-tools
modprobe pps_ldisc
setserial -v /dev/ttyS0 low_latency
ldattach PPS /dev/ttyS0

Check PPS signal: 

# ppstest /dev/pps0
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1733262552.000005797, sequence: 308579 - clear  1733262552.499996498, sequence: 308580
source 0 - assert 1733262553.000004664, sequence: 308580 - clear  1733262552.499996498, sequence: 308580
source 0 - assert 1733262553.000004664, sequence: 308580 - clear  1733262553.500003597, sequence: 308581
source 0 - assert 1733262554.000004920, sequence: 308581 - clear  1733262553.500003597, sequence: 308581
source 0 - assert 1733262554.000004920, sequence: 308581 - clear  1733262554.500000766, sequence: 308582

# ppscheck /dev/ttyS0
...
 KPPS  1733262666.000002906    assert  308693
 KPPS  1733262665.500002983    clear   308693
 
 KPPS  1733262666.499814138    clear   308694
 KPPS  1733262666.999988850    assert  308694

ppscheck /dev/ttyS0

Can set at boot with udev rule (/etc/udev/rules.d/gps.rules): 

KERNEL=="ttyS0", SYMLINK+="gps0"
KERNEL=="ttyS0", RUN+="/usr/bin/setserial -v /dev/%k low_latency"
KERNEL=="ttyS0", RUN+="/usr/sbin/ldattach PPS /dev/%k"
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