diff --git a/firmware/ice40-riscv/icE1usb/gps.c b/firmware/ice40-riscv/icE1usb/gps.c
new file mode 100644
index 0000000..2fd6ab8
--- /dev/null
+++ b/firmware/ice40-riscv/icE1usb/gps.c
@@ -0,0 +1,286 @@
+/*
+ * gps.c
+ *
+ * Copyright (C) 2019-2022  Sylvain Munaut <tnt@246tNt.com>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include <stddef.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+
+#include "console.h"
+#include "gps.h"
+#include "misc.h"
+#include "utils.h"
+
+#include "config.h"
+
+
+struct gps_uart {
+	uint32_t data;
+	uint32_t csr;
+} __attribute__((packed,aligned(4)));
+
+#define GPS_UART_CSR_DIV(baud)	((SYS_CLK_FREQ+(baud)/2)/(baud)-2)
+#define GPS_UART_CSR_TX_EMPTY	(1 << 29)
+#define GPS_UART_DATA_EMPTY	(1 << 31)
+
+static volatile struct gps_uart * const gps_uart_regs = (void*)(GPS_UART_BASE);
+
+
+static struct {
+	/* NMEA rx state */
+	struct {
+		enum {
+			GNS_WAIT   = 0,
+			GNS_READ   = 1,
+			GNS_CK_HI  = 2,
+			GNS_CK_LO  = 3,
+			GNS_END_CR = 4,
+			GNS_END_LF = 5,
+		} state;
+
+		int     len;
+		uint8_t cksum;
+		char    buf[95];	/* Max length is actually 82 + 1 (\0) */
+	} nmea;
+
+	/* Current lock state */
+	struct {
+		bool valid;
+	} fix;
+
+	/* Reported antenna state */
+	enum gps_antenna_state antenna;
+} g_gps;
+
+
+static void
+_gps_empty(bool wait_eol)
+{
+	bool eol = false;
+
+	uint32_t c;
+	while (1) {
+		c = gps_uart_regs->data;
+		if (c & GPS_UART_DATA_EMPTY) {
+			if (!wait_eol || eol)
+				break;
+		} else {
+			eol = (c == '\n');
+		}
+	}
+}
+
+static void
+_gps_send(const char *s)
+{
+	char cksum = 0;
+
+	/* Start sentence */
+	gps_uart_regs->data = '$';
+
+	/* Send payload */
+	while (*s)
+		cksum ^= (gps_uart_regs->data = *s++);
+
+	/* Send checksum */
+	gps_uart_regs->data = '*';
+
+	s = hexstr(&cksum, 1, false);
+	gps_uart_regs->data = *s++;
+	gps_uart_regs->data = *s++;
+
+	gps_uart_regs->data = '\r';
+	gps_uart_regs->data = '\n';
+}
+
+static const char *
+_gps_query(void)
+{
+	uint32_t c;
+	while (1) {
+		/* Get next char */
+		c = gps_uart_regs->data;
+		if (c & GPS_UART_DATA_EMPTY)
+			break;
+
+		/* Always store it */
+		if (g_gps.nmea.len == sizeof(g_gps.nmea.buf))
+			g_gps.nmea.state = GNS_WAIT;
+		else
+			g_gps.nmea.buf[g_gps.nmea.len++] = c;
+
+		/* State */
+		if (c == '$') {
+			/* '$' always triggers reset */
+			g_gps.nmea.state  = GNS_READ;
+			g_gps.nmea.cksum  = 0;
+			g_gps.nmea.len    = 1;
+			g_gps.nmea.buf[0] = '$';
+		} else {
+			switch (g_gps.nmea.state) {
+			case GNS_READ:
+				if (c == '*')
+					g_gps.nmea.state = GNS_CK_HI;
+				else
+					g_gps.nmea.cksum ^= c;
+				break;
+			case GNS_CK_HI:
+				g_gps.nmea.cksum ^= hexval(c) << 4;
+				g_gps.nmea.state = GNS_CK_LO;
+				break;
+			case GNS_CK_LO:
+				g_gps.nmea.cksum ^= hexval(c);
+				g_gps.nmea.state = GNS_END_CR;
+				break;
+			case GNS_END_CR:
+				g_gps.nmea.state = (c == '\r') ? GNS_END_LF : GNS_WAIT;
+				break;
+			case GNS_END_LF:
+				g_gps.nmea.state = GNS_WAIT;
+				g_gps.nmea.buf[g_gps.nmea.len] = 0x00;
+				if (c == '\n')
+					return g_gps.nmea.buf;
+				break;
+			default:
+				g_gps.nmea.state = GNS_WAIT;
+				g_gps.nmea.len   = 0;
+				break;
+			}
+		}
+	}
+	return NULL;
+}
+
+void
+_gps_parse_nmea(const char *nmea)
+{
+	/* Very basic parsing, we just look at GSA messages and consider
+	 * that if we have a 3D fix with PDOP < 5, the timing data should
+	 * be usable
+	 */
+	if (!strncmp(nmea, "$GPGSA", 6))
+	{
+		/* Check for Autonomous 3D fix (fixed field positions) */
+		if ((nmea[7] != 'A') || (nmea[9] != '3')) {
+			g_gps.fix.valid = false;
+			return;
+		}
+
+		/* Find PDOP */
+		const char *p = nmea;
+		for (int i=0; (i < 15) && (*p != '*'); i += (*(p++)==',') );
+
+		/* Is it low enough ? */
+		g_gps.fix.valid = (p[1] < '5');
+	}
+
+	/* Parse TXT ANTENNA Status */
+	if (!strncmp(nmea, "$GPTXT", 6) && nmea[13] == '0' && nmea[14] == '1')
+	{
+		if      (!strncmp(&nmea[16], "ANTENNA OK",    10))
+			g_gps.antenna = ANT_OK;
+		else if (!strncmp(&nmea[16], "ANTENNA OPEN",  12))
+			g_gps.antenna = ANT_OPEN;
+		else if (!strncmp(&nmea[16], "ANTENNA SHORT", 13))
+			g_gps.antenna = ANT_SHORT;
+		else
+			g_gps.antenna = ANT_UNKNOWN;
+	}
+}
+
+
+bool
+gps_has_valid_fix(void)
+{
+	return g_gps.fix.valid;
+}
+
+enum gps_antenna_state
+gps_antenna_status(void)
+{
+	return g_gps.antenna;
+}
+
+void
+gps_poll(void)
+{
+	const char *nmea;
+
+	/* Check if we have anything from the module */
+	nmea = _gps_query();
+	if (!nmea)
+		return;
+
+	/* If we do, process it locally to update our state */
+	_gps_parse_nmea(nmea);
+}
+
+void
+gps_init(void)
+{
+	int i;
+
+	/* State init */
+	memset(&g_gps, 0x00, sizeof(g_gps));
+
+	/* Configure reset gpio */
+	gpio_out(3, false);
+	gpio_dir(3, true);
+
+	/* Attempt reset sequence at 9600 baud and then 115200 baud */
+	for (i=0; i<2; i++)
+	{
+		uint32_t start_time = time_now_read();
+		bool init_ok;
+
+		/* Assert reset */
+		gpio_out(3, false);
+
+		/* Configure uart and empty buffer */
+		gps_uart_regs->csr = i ? GPS_UART_CSR_DIV(115200) : GPS_UART_CSR_DIV(9600);
+		_gps_empty(false);
+
+		/* Wait 100 ms */
+		delay(100);
+
+		/* Release reset line */
+		gpio_out(3, true);
+
+		/* Wait for first line of output as sign it's ready, timeout after 1s */
+		while (!time_elapsed(start_time, SYS_CLK_FREQ))
+			if ((init_ok = (_gps_query() != NULL)))
+				break;
+
+		if (init_ok) {
+			printf("[+] GPS ok at %d baud\n", i ? 115200 : 9600);
+			break;
+		}
+	}
+
+	/* Failed ? */
+	if (i == 2) {
+		printf("[!] GPS init failed\n");
+		return;
+	}
+
+	/* If success was at 9600 baud, need to speed up */
+	if (i == 0) {
+		/* Configure GPS to use serial at 115200 baud */
+		_gps_send("PCAS01,5");
+
+		/* Add dummy byte which will be mangled during baudrate switch ... */
+		gps_uart_regs->data = 0x00;
+		while (!(gps_uart_regs->csr & GPS_UART_CSR_TX_EMPTY));
+
+		/* Set uart to 115200 and empty uart buffer, line aligned */
+		gps_uart_regs->csr = GPS_UART_CSR_DIV(115200) ;
+		_gps_empty(true);
+	}
+
+	/* Configure GPS to be GPS-only (no GLONASS/BEIDOU) */
+	_gps_send("PCAS04,1");
+}