xiaoxiang781216 commented on code in PR #8483:
URL: https://github.com/apache/nuttx/pull/8483#discussion_r1106188619
##########
drivers/serial/serial.c:
##########
@@ -485,6 +489,87 @@ static int uart_tcdrain(FAR uart_dev_t *dev,
return ret;
}
+/****************************************************************************
+ * Name: uart_tcsendbreak
+ *
+ * Description:
+ * Request a serial line Break by calling the lower half driver's
+ * BSD-compatible Break IOCTLs TIOCSBRK and TIOCCBRK, with a sleep of the
+ * specified duration between them.
+ *
+ * Input Parameters:
+ * dev - Serial device.
+ * filep - Required for issuing lower half driver IOCTL call.
+ * ms - If non-zero, duration of the Break in milliseconds; if
+ * zero, duration is 400 milliseconds.
+ *
+ * Returned Value:
+ * 0 on success or a negated errno value on failure.
+ *
+ ****************************************************************************/
+
+static int uart_tcsendbreak(FAR uart_dev_t *dev, FAR struct file *filep,
+ unsigned int ms)
+{
+ int ret;
+
+ /* tcsendbreak is a cancellation point */
+
+ if (enter_cancellation_point())
+ {
+#ifdef CONFIG_CANCELLATION_POINTS
Review Comment:
should we move before line 518?
##########
libs/libc/termios/lib_tcsendbreak.c:
##########
@@ -0,0 +1,112 @@
+/****************************************************************************
+ * libs/libc/termios/lib_tcsendbreak.c
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership. The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <sys/ioctl.h>
+
+#include <termios.h>
+#include <errno.h>
+
+#include <nuttx/serial/tioctl.h>
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: tcsendbreak
+ *
+ * Description:
+ * Transmit a serial line Break, which is a continuous stream of 0 bits.
+ *
+ * A proper Break needs to last longer than a NUL ('\0') character.
+ * Effectively this causes a Framing Error at the receiver's UART. Most
+ * UARTs have the ability to distinguish between a Break and other types
+ * of Framing Errors and may treat it specially. Some devices utilize
+ * Breaks for things like synchronization.
+ *
+ * Regarding the duration parameter and its portability between Unix-like
+ * systems: It seems that a duration parameter of 0 specifies a Break of
+ * 0.25 to 0.5 seconds with consistency between various Unix flavors, but
+ * the interpretation of a nonzero duration parameter varies wildly from
+ * one operating system to another:
+ *
+ * - Linux, AIX, Tru64: duration in milliseconds
+ * - BSDs, macOS, HP-UX: ignore duration
+ * - Solaris, UnixWare: behaves like tcdrain()
+ *
+ * On FreeBSD and OpenBSD, a duration of 0 gives a Break of 0.4 seconds.
+ *
+ * Sources of information about the duration parameter include: the man
+ * page for termios(3) as found in release 5.13 of the Linux man-pages
+ * project, the man page for tcsendbreak(3) as found in FreeBSD 13.1 and
+ * OpenBSD 7.2, and some StackOverflow search results.
+ *
+ * In NuttX, we combine the above treatments of duration: Zero or negative
+ * values will give a Break of 0.4 seconds; positive values will be
+ * treated as a duration in milliseconds. We hope this combination will
+ * work well for programs that are ported from any of the above families.
+ *
+ * NuttX-specific implementation details: tcsendbreak() calls IOCTL
+ * TCSBRK. This is handled in the upper half serial driver (see
+ * drivers/serial/serial.c), which treats its argument like 'duration'
+ * described here, except unsigned, supporting only 0 or positive values;
+ * 0 maps to 400 and all other values are used as-is, in milliseconds.
+ * This, in turn, calls IOCTLs TIOCSBRK and TIOCCBRK to start and end a
+ * BSD-compatible Break, respectively, with a sleep of the given duration
+ * between them. For tcsendbreak() to work, the arch-specific lower half
+ * serial driver must implement TIOCSBRK and TIOCCBRK. Some architectures
+ * do not implement these at all. Others implement them but rely upon one
+ * or more Kconfig options being set, such as CONFIG_*_U[S]ART_BREAKS and,
+ * on some architectures, a separate CONFIG_*_SERIALBRK_BSDCOMPAT, to
+ * provide the required Break behavior. Furthermore, the sleep time will
+ * be at least the given duration, but may be substantially longer
+ * depending on the system's tick resolution (see CONFIG_USEC_PER_TICK)
+ * and other factors.
+ *
+ * This function blocks for the duration of the Break.
+ *
+ * Input Parameters:
+ * fd - The 'fd' argument is an open file descriptor associated
+ * with a terminal.
+ * duration - If 0 or negative, request a serial line Break lasting 0.4
+ * seconds. If non-zero, request a serial line Break lasting
+ * that duration in milliseconds.
+ *
+ * Returned Value:
+ * Upon successful completion, 0 is returned. Otherwise, -1 is returned
+ * and errno is set to indicate the error.
+ *
+ ****************************************************************************/
+
+int tcsendbreak(int fd, int duration)
+{
+ if (duration <= 0)
+ {
+ duration = 400;
+ }
+
+ return ioctl(fd, TCSBRK, (unsigned long) duration);
Review Comment:
```suggestion
return ioctl(fd, TCSBRK, (unsigned long)duration);
```
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