core: Add software UART implementation
This patch brings a Work-in-Progress implementation of the software
UART (Universal Asynchronous Receiver/Transmitter) to libosmocore.
Not only it will be useful in the context of retro-networking, but
also it's needed for the MS-side CSD implementation (see OS#4396).
It should be noted that the definition of struct osmo_soft_uart
is intentionally kept private, since the API is not stable yet.
Currently, the following limitations apply:
* Only the receiver part is implemented, the transmitter is TBD.
* Parity checking is not implemented in the receiver part.
* Software flow control is not implemented.
These missing components will be addressed in subsequent patches.
Change-Id: I2ca95963fd5852ddb89bdd35b86b31489127fe84
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;
+}