A script used for testing passing correction data over USB with two SkytraQ GPS units connected via USB to one laptop.

com6tocom10.py

'''
com6tocom10.py
This is a script used for testing passing correction data over USB with two GPS units connected 
to one laptop.  The script performs these functions:
1. Forward RTCM correction data from my Base GNSS receiver, a SkytraQ PX1125R, connected on (COM6) to a 
Rover GNSS receiver (COM10). 
2. Monitor NMEA messages from my Rover, a Skytraq PX1172RDP, on COM10 and extract RTK Fix status 
from $GPGGA messages. 
3. Print the RTK Fix status every 5 seconds along with the last $GPGGA message.
'''


import serial
import threading
import time

# Assigning COM ports
BASE_PORT = "COM6"   # PX1125R (Base station, sending RTCM)
ROVER_PORT = "COM10"  # PX1172RDP (Rover, receiving RTCM + outputting NMEA)
BAUD_RATE = 115200
STATUS_INTERVAL = 5  # Print RTK status every 5 seconds

rover = None  # Shared COM10 connection

def open_serial(port):
    """Attempts to open a serial port."""
    try:
        ser = serial.Serial(port, BAUD_RATE, timeout=1)
        print(f"Successfully opened {port}.")
        return ser
    except serial.SerialException as e:
        print(f"Error opening {port}: {e}")
        return None

def forward_rtcm():
    """Reads RTCM data from Base and forwards it to Rover."""
    global rover

    rover = open_serial(ROVER_PORT)  # Open COM10 first
    base = open_serial(BASE_PORT)  # Open COM6

    if not base or not rover:
        print("Failed to open one or both ports. Exiting RTCM forwarding.")
        return

    print(f"Forwarding RTCM data from {BASE_PORT} to {ROVER_PORT}...")
    try:
        while True:
            data = base.read(4096)  # Read RTCM data in chunks
            if data:
                rover.write(data)  # Send RTCM to Rover
                time.sleep(0.01)  # Short delay to prevent overloading buffer
    except Exception as e:
        print(f"Error in RTCM forwarding: {e}")
    finally:
        base.close()
        rover.close()

def monitor_nmea():
    """Reads NMEA output from Rover and prints RTK status every 5 seconds with last GGA message."""
    global rover

    print("Waiting for Rover (COM10) to be ready...")
    while rover is None:  # Wait until `forward_rtcm` opens COM10
        time.sleep(1)

    print(f"Listening to NMEA data from {ROVER_PORT}...")
    last_status_time = time.time()
    last_gga_message = None  # Store last GGA message

    try:
        while True:
            line = rover.readline().decode(errors='ignore').strip()
            if line.startswith("$GPGGA"):  # Extract RTK status every 5 seconds
                last_gga_message = line  # Store the last GGA message
                current_time = time.time()
                if current_time - last_status_time >= STATUS_INTERVAL:
                    fields = line.split(',')
                    fix_type = fields[6]
                    num_satellites = fields[7]
                    altitude = fields[9]

                    status = {
                        "0": "No Fix",
                        "1": "GPS Fix",
                        "2": "DGPS Fix",
                        "4": "RTK Fixed",
                        "5": "RTK Float"
                    }.get(fix_type, "Unknown")

                    print(f"[{time.strftime('%H:%M:%S')}] RTK Status: {status} | Satellites: {num_satellites} | Altitude: {altitude}m")
                    print(f"Last GGA Message: {last_gga_message}")  # Print full GGA message
                    last_status_time = current_time  # Reset timer

    except Exception as e:
        print(f"Error in NMEA monitoring: {e}")

# Run both functions in parallel
rtcm_thread = threading.Thread(target=forward_rtcm, daemon=True)
nmea_thread = threading.Thread(target=monitor_nmea, daemon=True)

rtcm_thread.start()
nmea_thread.start()

# Keep script running
try:
    while True:
        time.sleep(1)
except KeyboardInterrupt:
    print("\nExiting...")