GPS Module: Difference between revisions
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PPS | 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 | |||
* Configure in u-Center [[Media:u-Center Configuration.png|here]] | * Configure in u-Center [[Media:u-Center Configuration.png|here]] | ||
== Software == | == Software == | ||
Revision as of 13:15, 31 May 2024
HW-595 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
- Configure in u-Center here
Software
U-Center
- U-Center
- Select COM port and Baud rate
- Communicates with uBlox with binary UBX Protocol
View/Change Settings (View -> Configuration View), Send to activate change:
- PRT (Ports)
- Baud Rate : 9600 -> 115200
- TP5 (Timepulse 5)
- Frequency : 1 Hz -> 10 Hz
- Duty Cycle : 100% -> 25%
- Frequency Locked : 1 Hz
- Duty Locked : 50%
- Rising Edge on TOS
- Cable Delay : 50 ns -> 10 ns (compensates for cable delay between antenna and receiver)
- UBX -> CFG (Config) -> CFG (Configuration) [Save accross reboots]
- Select 2-I2C-EEPROM in the Devices option
Save accross reboots (view -> Message View):
- Firmware version: UBX -> MON (Monitor) -> VER (Version)
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
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
Can show raw data:
gpscat /dev/ttyS0
Enable and start gpsd:
systemctl enable gpsd systemctl start gpsd
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 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"