Hardware Setup

HAT Variants

HAT	u-blox Module	Communication	USB Port	Key Features
L1 GNSS HAT	NEO-M9N	SPI	Yes	Standard positioning, geofencing
L1/L5 GNSS TIME HAT	NEO-F10T	UART	—	Dual-band, time base, time mark
L1/L5 GNSS RTK HAT	NEO-F9P	SPI + UART	Yes	Dual-band, RTK base/rover, geofencing

Auto-Detection

The library automatically identifies which HAT is installed by reading:

/proc/device-tree/hat/product

You do not need to specify the HAT type in code — IGnssHat::create() (C++) / gnsshat.GnssHat() (Python) / jp_gnss_hat_create() (C) handles detection and returns the correct implementation.

GPIO Pin Mapping

GPIO Pin	Function	Used By
GPIO 5	Timepulse (PPS) output	All HATs — 1PPS signal from u-blox module
GPIO 17	TxReady (SPI HATs) / EXTINT (TIME HAT)	L1 & RTK: data-ready interrupt. TIME: time mark input
PIO pin 6	Geofence status output	L1 & RTK HATs — drives LED/relay on HAT

Note

GPIO 5 Conflict — Kernel PPS (/dev/pps0) and the library’s enableTimepulse() / timepulse() both use GPIO 5. They cannot run at the same time. Choose one or the other.

Communication Interfaces

SPI (L1 HAT, RTK HAT)

The NEO-M9N (L1 HAT) and NEO-F9P (RTK HAT) communicate over SPI. The library uses a TxReady interrupt on GPIO 17 to know when data is available — no polling.

SPI requires root privileges or membership in the spi group.

UART (TIME HAT, RTK HAT secondary)

The NEO-F10T (TIME HAT) uses UART as its primary interface. The NEO-F9P (RTK HAT) uses UART as a secondary channel for RTCM3 corrections.

UART must be enabled via raspi-config (see Installation).

USB (L1 HAT, RTK HAT)

The L1 HAT and RTK HAT expose the u-blox module’s USB port. When connected via USB cable to the Pi, the module appears as /dev/ttyACM0 (CDC-ACM serial device). This is useful for:

Direct gpsd access without the bridge daemon
u-blox u-center configuration tool
Firmware updates

Note

USB access bypasses the library entirely. Use it for gpsd or u-center, not alongside the library’s SPI communication.

Antenna

All HATs have an on-board antenna connector and support active antennas. The library reports antenna status (OK, Short, Open) and power state via the rfBlocks field in navigation data.

For best performance:

Place the antenna with a clear view of the sky
Use an active antenna for improved signal strength
The module reports AntennaStatus::Open if no antenna is detected