USB operation¶

On the mini carrier everything goes through the USB-C port: power, RTK corrections in, NMEA output and SBF logs. This page describes the operating flow.

USB connection¶

When the Main (mosaic-X5 module) is connected to a PC via USB-C, the module presents itself to the host with two kinds of interface at the same time:

one or more virtual serial (COM) ports – carrying the data (NMEA, SBF) and used to send commands/corrections;
an IP-over-USB interface at address 192.168.3.1, exposing the receiver's built-in web interface (browser configuration).

Tip

To configure the receiver just open http://192.168.3.1 in the browser after connecting USB: this opens the Septentrio web UI (status, ports, logging, RTK, etc.).

Operating-system compatibility¶

System	Recognised	Notes
Windows	Yes	Requires the Septentrio USB driver (included in RxTools).
Linux	Yes	Works with the standard CDC-ACM driver.
macOS	No (in our tests)	The device is not recognised.

Warning

On macOS the receiver, at least in our tests, is not recognised; on Windows and Linux it works normally.

Probable cause: the module's Ethernet-over-USB interface (the virtual network that exposes the web UI at 192.168.3.1) uses the RNDIS protocol, which macOS does not support natively. Windows and Linux, on the other hand, include RNDIS / CDC-ACM support. (observed behaviour; awaiting a solution/driver for macOS)

Data flow¶

PC / Device                              Main MSX (mosaic-X5)
───────────                              ────────────────────
NTRIP client ──RTCM3──►  USB (COM)  ──►  ingresso correzioni RTK
app di campo ◄──NMEA──   USB (COM)  ◄──  uscita posizione (GGA, RMC…)
logger       ◄──SBF───   USB (COM)  ◄──  dati grezzi (logging)
browser      ◄─web UI─   USB-IP 192.168.3.1

RTK corrections¶

RTK corrections are received always and only through an external NTRIP client (on the PC or the device), never by the receiver on its own. The NTRIP client:

connects to the NTRIP caster (network of permanent stations) over the Internet;
downloads the RTCM 3.x correction stream;
forwards it to a USB COM port of the receiver.

The module applies the corrections and, under open sky, quickly goes from single solution to RTK fixed (centimetre precision).

Info

The MSX system has no internal NTRIP client: corrections come exclusively from an external NTRIP client that forwards them to the USB COM port. The client can be the one built into the field software or a dedicated utility (e.g. Data Link from Septentrio RxTools).

NMEA output¶

The position is output in NMEA-0183 on a USB COM port, so it can be read by any GIS/survey app. Typical sentences:

Sentence	Content
`GGA`	position (lat/lon/altitude), fix quality, no. of satellites
`RMC`	position, speed, date/time
`GSA` / `GSV`	satellites used and in view, DOP
`VTG`	course and ground speed
`ZDA`	UTC date and time
`GST`	position error statistics

The NMEA output, its rate and the active sentences are set from the web UI (http://192.168.3.1 → ports/outputs) or via a command on the port.

Note

The NMEA output rate is independent of the SBF logging rate: you can, for example, output NMEA at 1–10 Hz to the app and record SBF at a higher rate in parallel (see SBF logging).

Quick start¶

Antenna: connect the active GNSS antenna and place it under open sky.
USB: connect the Main to the PC with a USB-C data cable (not charge-only).
Web UI: open http://192.168.3.1 and check the satellite status.
RTK: start the NTRIP client and forward the RTCM to the receiver's COM port.
NMEA: configure the NMEA output on the COM port used by the field app.
Check: wait for the transition to RTK fixed (see Main board).