diff --git a/include/osmocom/core/Makefile.am b/include/osmocom/core/Makefile.am
index e1b52d5..7c29ca1 100644
--- a/include/osmocom/core/Makefile.am
+++ b/include/osmocom/core/Makefile.am
@@ -60,6 +60,7 @@
 	utils.h \
 	write_queue.h \
 	sockaddr_str.h \
+	soft_uart.h \
 	time_cc.h \
 	use_count.h \
 	socket_compat.h \
diff --git a/include/osmocom/core/soft_uart.h b/include/osmocom/core/soft_uart.h
new file mode 100644
index 0000000..36a43fe
--- /dev/null
+++ b/include/osmocom/core/soft_uart.h
@@ -0,0 +1,85 @@
+#pragma once
+
+/*! \file soft_uart.h
+ *  Software UART implementation. */
+/*
+ * (C) 2022 by Harald Welte <laforge@gnumonks.org>
+ *
+ * All Rights Reserved
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#include <stdint.h>
+#include <osmocom/core/bits.h>
+#include <osmocom/core/msgb.h>
+
+enum osmo_soft_uart_parity_mode {
+	OSMO_SUART_PARITY_NONE,
+	OSMO_SUART_PARITY_EVEN,
+	OSMO_SUART_PARITY_ODD,
+	_OSMO_SUART_PARITY_NUM
+};
+
+enum osmo_soft_uart_flags {
+	OSMO_SUART_F_FRAMING_ERROR	= (1 << 0),
+	OSMO_SUART_F_PARITY_ERROR	= (1 << 1),
+	OSMO_SUART_F_BREAK		= (1 << 2),
+};
+
+#if 0
+enum osmo_soft_uart_status {
+	/* RTS, CTS, ... */
+	_fixme,
+};
+#endif
+
+/* configuration for a soft-uart */
+struct osmo_soft_uart_cfg {
+	/*! number of data bits (typically 5, 6, 7 or 8) */
+	uint8_t num_data_bits;
+	/*! number of stop bots (typically 1 or 2) */
+	uint8_t num_stop_bits;
+	/*! parity mode (none, even, odd) */
+	enum osmo_soft_uart_parity_mode parity_mode;
+	/*! size of receive buffer; UART will buffer up to that number of characters
+	 *  before calling the receive call-back */
+	unsigned int rx_buf_size;
+	/*! receive timeout; UART will flush receive buffer via the receive call-back
+	 * after indicated number of milli-seconds even if it is not full yet */
+	unsigned int rx_timeout_ms;
+
+	/*! opaque application-private data; passed to call-backs */
+	void *priv;
+
+	/*! receive call-back. Either rx_buf_size characters were received or rx_timeout_ms
+	 * expired, or an error flag was detected (related to last byte received).
+	 * 'flags' is a bit-mask of osmo_soft_uart_flags,  */
+	void (*rx_cb)(void *priv, struct msgb *rx_data, unsigned int flags);
+
+	/*! modem status line change call-back. gets bitmask of osmo_soft_uart_status */
+	void (*status_change_cb)(void *priv, unsigned int status);
+};
+
+struct osmo_soft_uart;
+
+struct osmo_soft_uart *osmo_soft_uart_alloc(void *ctx, const char *name);
+int osmo_soft_uart_configure(struct osmo_soft_uart *suart, const struct osmo_soft_uart_cfg *cfg);
+int osmo_soft_uart_enable(struct osmo_soft_uart *suart, bool rx, bool tx);
+
+int osmo_soft_uart_rx_ubits(struct osmo_soft_uart *suart, const ubit_t *ubits, size_t n_ubits);
+int osmo_soft_uart_tx_ubits(struct osmo_soft_uart *suart, ubit_t *ubits, size_t n_ubits);
+
+void osmo_soft_uart_tx(struct osmo_soft_uart *suart, struct msgb *tx_data);
+int osmo_soft_uart_set_status(struct osmo_soft_uart *suart, unsigned int status);
diff --git a/src/core/Makefile.am b/src/core/Makefile.am
index 326c68d..2efebd8 100644
--- a/src/core/Makefile.am
+++ b/src/core/Makefile.am
@@ -63,6 +63,7 @@
 	signal.c \
 	sockaddr_str.c \
 	socket.c \
+	soft_uart.c \
 	stat_item.c \
 	stats.c \
 	stats_statsd.c \
diff --git a/src/core/libosmocore.map b/src/core/libosmocore.map
index e5f8bd8..c08d3ff 100644
--- a/src/core/libosmocore.map
+++ b/src/core/libosmocore.map
@@ -439,6 +439,13 @@
 osmo_sock_set_priority;
 osmo_sock_unix_init;
 osmo_sock_unix_init_ofd;
+osmo_soft_uart_alloc;
+osmo_soft_uart_configure;
+osmo_soft_uart_enable;
+osmo_soft_uart_rx_ubits;
+osmo_soft_uart_tx_ubits;
+osmo_soft_uart_tx;
+osmo_soft_uart_set_status;
 osmo_stat_item_dec;
 osmo_stat_item_flush;
 osmo_stat_item_for_each_group;
diff --git a/src/core/soft_uart.c b/src/core/soft_uart.c
new file mode 100644
index 0000000..22292af
--- /dev/null
+++ b/src/core/soft_uart.c
@@ -0,0 +1,268 @@
+/*! \file soft_uart.c
+ *  Software UART implementation. */
+/*
+ * (C) 2022 by Harald Welte <laforge@gnumonks.org>
+ *
+ * All Rights Reserved
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <errno.h>
+
+#include <osmocom/core/timer.h>
+#include <osmocom/core/soft_uart.h>
+
+/*! one instance of a soft-uart */
+struct osmo_soft_uart {
+	struct osmo_soft_uart_cfg cfg;
+	const char *name;
+	struct {
+		bool running;
+		uint8_t bit_count;
+		uint8_t shift_reg;
+		struct msgb *msg;
+		ubit_t parity_bit;
+		unsigned int flags;
+		unsigned int status;
+		struct osmo_timer_list timer;
+	} rx;
+	struct {
+		bool running;
+		uint8_t bit_count;
+		uint8_t shift_reg;
+		struct msgb *msg;
+		struct llist_head queue;
+	} tx;
+};
+
+static struct osmo_soft_uart_cfg suart_default_cfg = {
+	.num_data_bits = 8,
+	.num_stop_bits = 1,
+	.parity_mode = OSMO_SUART_PARITY_NONE,
+	.rx_buf_size = 1024,
+	.rx_timeout_ms = 100,
+	.priv = NULL,
+	.rx_cb = NULL,
+	.status_change_cb = NULL,
+};
+
+/*************************************************************************
+ * Receiver
+ *************************************************************************/
+
+/* flush the receive buffer + allocate new one, as needed */
+static void suart_flush_rx(struct osmo_soft_uart *suart)
+{
+	if ((suart->rx.msg && msgb_length(suart->rx.msg)) || suart->rx.flags) {
+		osmo_timer_del(&suart->rx.timer);
+		if (suart->cfg.rx_cb) {
+			suart->cfg.rx_cb(suart->cfg.priv, suart->rx.msg, suart->rx.flags);
+			/* call-back has taken ownership of msgb, no need to free() here */
+			suart->rx.msg = msgb_alloc_c(suart, suart->cfg.rx_buf_size, "soft_uart rx");
+		} else {
+			msgb_reset(suart->rx.msg);
+		}
+	}
+}
+
+/* one character was received; add to receive buffer and notify user, if needed */
+static void suart_rx_ch(struct osmo_soft_uart *suart, uint8_t ch)
+{
+	unsigned int msg_len;
+
+	OSMO_ASSERT(suart->rx.msg);
+	msgb_put_u8(suart->rx.msg, ch);
+	msg_len = msgb_length(suart->rx.msg);
+
+	/* first character in new message: start timer */
+	if (msg_len == 1) {
+		osmo_timer_schedule(&suart->rx.timer, suart->cfg.rx_timeout_ms / 1000,
+				    (suart->cfg.rx_timeout_ms % 1000) * 1000);
+	} else if (msg_len >= suart->cfg.rx_buf_size || suart->rx.flags) {
+		suart_flush_rx(suart);
+	}
+}
+
+/* receive a single bit */
+static inline void osmo_uart_rx_bit(struct osmo_soft_uart *suart, const ubit_t bit)
+{
+	unsigned int num_parity_bits = 0;
+
+	if (!suart->rx.running)
+		return;
+
+	if (suart->rx.bit_count == 0) {
+		/* start bit is 0.  Wait if there is none */
+		if (bit == 0) {
+			/* START bit */
+			suart->rx.flags = 0;
+			suart->rx.shift_reg = 0;
+			suart->rx.bit_count++;
+		}
+		return;
+	}
+
+	if (suart->cfg.parity_mode != OSMO_SUART_PARITY_NONE)
+		num_parity_bits = 1;
+
+	suart->rx.bit_count++;
+	if (suart->rx.bit_count <= 1 + suart->cfg.num_data_bits) {
+		/* DATA bit */
+		suart->rx.shift_reg = suart->rx.shift_reg >> 1;
+		if (bit)
+			suart->rx.shift_reg |= 0x80;
+	} else if (suart->cfg.parity_mode != OSMO_SUART_PARITY_NONE &&
+		   suart->rx.bit_count == 1 + suart->cfg.num_data_bits + 1) {
+		/* PARITY bit */
+		suart->rx.parity_bit = bit;
+		/* TODO: verify parity */
+		//suart->rx.flags |= OSMO_SUART_F_PARITY_ERROR;
+	} else if (suart->rx.bit_count <=
+		   1 + suart->cfg.num_data_bits + num_parity_bits + suart->cfg.num_stop_bits) {
+		/* STOP bit */
+		if (bit != 1) {
+			fprintf(stderr, "framing error: stop bit %u != 1\n", suart->rx.bit_count);
+			suart->rx.flags |= OSMO_SUART_F_FRAMING_ERROR;
+		}
+
+		if (suart->rx.bit_count == 1 + suart->cfg.num_data_bits + num_parity_bits + suart->cfg.num_stop_bits) {
+			//printf("Rx: 0x%02x %c\n", suart->rx.shift_reg, suart->rx.shift_reg);
+			suart_rx_ch(suart, suart->rx.shift_reg);
+			suart->rx.bit_count = 0;
+		}
+	}
+}
+
+/* receive timer expiration: flush rx-buffer to user call-back */
+static void suart_rx_timer_cb(void *data)
+{
+	struct osmo_soft_uart *suart = data;
+	suart_flush_rx(suart);
+}
+
+/*! feed a number of unpacked bits into the soft-uart receiver */
+int osmo_soft_uart_rx_ubits(struct osmo_soft_uart *suart, const ubit_t *ubits, size_t n_ubits)
+{
+	for (size_t i = 0; i < n_ubits; i++)
+		osmo_uart_rx_bit(suart, ubits[i]);
+	return 0;
+}
+
+/*************************************************************************
+ * Transmitter
+ *************************************************************************/
+
+/*! enqueue the given message buffer into the transmit queue of the UART. */
+void osmo_soft_uart_tx(struct osmo_soft_uart *suart, struct msgb *tx_data)
+{
+	if (!suart->tx.msg)
+		suart->tx.msg = tx_data;
+	else
+		msgb_enqueue(&suart->tx.queue, tx_data);
+}
+
+/* pull a single bit out of the UART transmitter */
+static inline ubit_t osmo_uart_tx_bit(struct osmo_soft_uart *suart)
+{
+	if (!suart->tx.running)
+		return 1;
+
+	if (suart->tx.bit_count == 0) {
+		/* do we have anything to transmit? */
+		/* FIXME */
+	}
+	/* FIXME */
+	return 1;
+}
+
+/*! pull then number of specified unpacked bits out of the UART Transmitter */
+int osmo_soft_uart_tx_ubits(struct osmo_soft_uart *suart, ubit_t *ubits, size_t n_ubits)
+{
+	for (size_t i = 0; i < n_ubits; i++)
+		ubits[i] = osmo_uart_tx_bit(suart);
+	return n_ubits;
+}
+
+/*! Set the modem status lines of the UART */
+int osmo_soft_uart_set_status(struct osmo_soft_uart *suart, unsigned int status)
+{
+	/* FIXME: Tx */
+	return 0;
+}
+
+
+/*************************************************************************
+ * Management / Initialization
+ *************************************************************************/
+
+struct osmo_soft_uart *osmo_soft_uart_alloc(void *ctx, const char *name)
+{
+	struct osmo_soft_uart *suart = talloc_zero(ctx, struct osmo_soft_uart);
+	if (!suart)
+		return NULL;
+	suart->name = talloc_strdup(suart, name);
+	suart->cfg = suart_default_cfg;
+
+	return suart;
+}
+
+/*! change soft-UART configuration to user-provided config */
+int osmo_soft_uart_configure(struct osmo_soft_uart *suart, const struct osmo_soft_uart_cfg *cfg)
+{
+	/* consistency checks on the configuration */
+	if (cfg->num_data_bits > 8 || cfg->num_data_bits == 0)
+		return -EINVAL;
+	if (cfg->num_stop_bits == 0)
+		return -EINVAL;
+	if (cfg->parity_mode < 0 || cfg->parity_mode >= _OSMO_SUART_PARITY_NUM)
+		return -EINVAL;
+	if (cfg->rx_buf_size == 0)
+		return -EINVAL;
+
+	if (suart->cfg.rx_buf_size > cfg->rx_buf_size ||
+	    suart->cfg.rx_timeout_ms > cfg->rx_timeout_ms) {
+		suart_flush_rx(suart);
+	}
+
+	suart->cfg = *cfg;
+
+	osmo_timer_setup(&suart->rx.timer, suart_rx_timer_cb, suart);
+	INIT_LLIST_HEAD(&suart->tx.queue);
+
+	return 0;
+}
+
+int osmo_soft_uart_enable(struct osmo_soft_uart *suart, bool rx, bool tx)
+{
+	if (!rx && suart->rx.running) {
+		suart_flush_rx(suart);
+		suart->rx.running = false;
+	} else if (rx && !suart->rx.running) {
+		if (!suart->rx.msg)
+			suart->rx.msg = msgb_alloc_c(suart, suart->cfg.rx_buf_size, "soft_uart rx");
+		suart->rx.running = true;
+	}
+
+	if (!tx && suart->tx.running) {
+		/* FIXME: Tx */
+		suart->tx.running = false;
+	} else if (tx && !suart->tx.running) {
+		suart->tx.running = true;
+	}
+
+	return 0;
+}