drivers/serial/tcdrain: tcdrain() was recently added to the NuttX C library. But there is a problem. The specification of tcdrain() requires that it be a cancellation point. In order to do this, tcdrain was moved from the C library into the OS and the addition cancellation point hooks were added. In non-FLAT builds, access via system calls is also now supported.

TODO

@@ -530,7 +530,7 @@ o pthreads (sched/pthreads)
              NA clock_nanosleep() NA msgsnd()                    read()             sigwaitinfo()
                 close()           NA msync()                  NA readv()         01 sleep()
                 connect()            nanosleep()                 recv()          02 system()
-             -- creat()              open()                      recvfrom()      NA tcdrain()
+             -- creat()              open()                      recvfrom()         tcdrain()
                 fcntl()              pause()                  NA recvmsg()       01 usleep()
              NA fdatasync()          poll()                      select()        -- wait()
                 fsync()              pread()                     sem_timedwait()    waitid()

arch/arm/src/lc823450/Kconfig

@@ -7,27 +7,22 @@ comment "LC823450 Configuration Options"
 
 menu "LC823450 Peripheral Support"
 
-config SERIAL_TERMIOS
-        bool "Serial driver TERMIOS supported"
-        default n
-        ---help---
-                Serial driver supports termios.h interfaces (tcsetattr, tcflush, etc.).
-                If this is not defined, then the terminal settings (baud, parity, etc).
-                are not configurable at runtime; serial streams cannot be flushed, etc..
-
 config LC823450_UART0
 	bool "UART0"
 	select UART0_SERIALDRIVER
+	select ARCH_HAVE_SERIAL_TERMIOS
 	default n
 
 config LC823450_UART1
 	bool "UART1"
 	select UART1_SERIALDRIVER
+	select ARCH_HAVE_SERIAL_TERMIOS
 	default n
 
 config LC823450_UART2
 	bool "UART2"
 	select UART2_SERIALDRIVER
+	select ARCH_HAVE_SERIAL_TERMIOS
 	default n
 
 config LC823450_WDT

arch/arm/src/lpc11xx/Kconfig

@@ -56,6 +56,7 @@ config LPC11_PLL
 config LPC11_UART0
 	bool "UART0"
 	select UART0_SERIALDRIVER
+	select ARCH_HAVE_SERIAL_TERMIOS
 	default y
 
 config LPC11_CAN0
@@ -100,20 +101,6 @@ config LPC11_FLASH
 
 endmenu
 
-menu "Serial driver options"
-	depends on LPC11_UART0 || LPC11_UART1 || LPC11_UART2 || LPC11_UART3 || LPC11_UART4
-
-config SERIAL_TERMIOS
-	bool "Serial driver TERMIOS supported"
-	depends on LPC11_UART0 || LPC11_UART1 || LPC11_UART2 || LPC11_UART3
-	default n
-	---help---
-		Serial driver supports termios.h interfaces (tcsetattr, tcflush, etc.).
-		If this is not defined, then the terminal settings (baud, parity, etc).
-		are not configurable at runtime; serial streams cannot be flushed, etc..
-
-endmenu
-
 menu "ADC driver options"
 	depends on LPC11_ADC
 

arch/avr/src/atmega/Kconfig

@@ -32,24 +32,12 @@ menu "ATMega Peripheral Selections"
 config AVR_USART0
 	bool "USART0"
 	select USART0_SERIALDRIVER
+	select ARCH_HAVE_SERIAL_TERMIOS
 
 config AVR_USART1
 	bool "USART1"
 	select USART1_SERIALDRIVER
+	select ARCH_HAVE_SERIAL_TERMIOS
 
 endmenu # ATMega Peripheral Selections
-
-menu "Low level USART driver options"
-	depends on AVR_USART0 || AVR_USART1
-
-config SERIAL_TERMIOS
-	bool "Serial driver TERMIOS supported"
-	depends on AVR_USART0 || AVR_USART1
-	default n
-	---help---
-		Serial driver supports termios.h interfaces (tcsetattr, tcflush, etc.).
-		If this is not defined, then the terminal settings (baud, parity, etc).
-		are not configurable at runtime; serial streams cannot be flushed, etc..
-
-endmenu
 endif

drivers/serial/Make.defs

@@ -1,7 +1,7 @@
 ############################################################################
 # drivers/serial/Make.defs
 #
-#   Copyright (C) 2009, 2011 Gregory Nutt. All rights reserved.
+#   Copyright (C) 2009, 2011, 2017 Gregory Nutt. All rights reserved.
 #   Author: Gregory Nutt <gnutt@nuttx.org>
 #
 # Redistribution and use in source and binary forms, with or without
@@ -47,6 +47,12 @@ ifeq ($(CONFIG_16550_UART),y)
   CSRCS += uart_16550.c
 endif
 
+# termios support
+
+ifeq ($(CONFIG_SERIAL_TERMIOS),y)
+  CSRCS += tcdrain.c
+endif
+
 # Pseudo-terminal support
 
 ifeq ($(CONFIG_PSEUDOTERM),y)

drivers/serial/tcdrain.c

@@ -1,5 +1,5 @@
 /****************************************************************************
- * libc/termios/lib_tcdrain.c
+ * drivers/serial/tcdrain.c
  *
  *   Copyright (C) 2017 Gregory Nutt. All rights reserved.
  *   Copyright (C) 2017 Sebastien Lorquet. All rights reserved.
@@ -45,6 +45,7 @@
 #include <termios.h>
 #include <errno.h>
 
+#include <nuttx/cancelpt.h>
 #include <nuttx/serial/tioctl.h>
 
 /****************************************************************************
@@ -68,5 +69,33 @@
 
 int tcdrain(int fd)
 {
-  return ioctl(fd, TCDRN, (unsigned long)0);
+  int ret;
+
+  /* tcdrain is a cancellation point */
+
+  if (enter_cancellation_point())
+    {
+#ifdef CONFIG_CANCELLATION_POINTS
+      /* If there is a pending cancellation, then do not perform
+       * the wait.  Exit now with ECANCELED.
+       */
+
+      set_errno(ECANCELED);
+      leave_cancellation_point();
+      return ERROR;
+#endif
+    }
+
+  /* Perform the TCDRM IOCTL command.  It is safe to use the file descriptor
+   * in this context because we are executing on the calling application's
+   * thread.
+   *
+   * NOTE: ioctl() will set the errno variable and return ERROR is any error
+   * occurs.
+   */
+
+  ret = ioctl(fd, TCDRN, (unsigned long)0);
+
+  leave_cancellation_point();
+  return ret;
 }

include/sys/syscall.h

@@ -298,9 +298,15 @@
 #  ifndef CONFIG_DISABLE_POLL
 #    define SYS_poll                   __SYS_poll
 #    define SYS_select                 (__SYS_poll+1)
-#    define __SYS_boardctl             (__SYS_poll+2)
+#    define __SYS_termios              (__SYS_poll+2)
 #  else
-#    define __SYS_boardctl             __SYS_poll
+#    define __SYS_termios               __SYS_poll
+#  endif
+#  ifndef CONFIG_SERIAL_TERMIOS
+#    define SYS_tcdrain                __SYS_termios
+#    define __SYS_boardctl             (__SYS_termios+1)
+#  else
+#    define __SYS_boardctl             __SYS_termios
 #  endif
 #else
 #  define __SYS_boardctl               __SYS_descriptors

libc/termios/Make.defs

@@ -42,7 +42,7 @@ ifeq ($(CONFIG_SERIAL_TERMIOS),y)
 # Add the termios C files to the build
 
 CSRCS += lib_cfgetspeed.c lib_cfsetspeed.c lib_isatty.c lib_tcflush.c
-CSRCS += lib_tcgetattr.c lib_tcsetattr.c lib_tcdrain.c
+CSRCS += lib_tcgetattr.c lib_tcsetattr.c
 
 # Add the termios directory to the build
 

syscall/syscall.csv

@@ -153,6 +153,7 @@
 "task_setcancelstate","sched.h","","int","int","FAR int*"
 "task_setcanceltype","sched.h","defined(CONFIG_CANCELLATION_POINTS)","int","int","FAR int*"
 "task_testcancel","pthread.h","defined(CONFIG_CANCELLATION_POINTS)","void"
+"tcdrain","termios.h","defined(CONFIG_SERIAL_TERMIOS)","int","int"
 "telldir","dirent.h","CONFIG_NFILE_DESCRIPTORS > 0","off_t","FAR DIR*"
 "timer_create","time.h","!defined(CONFIG_DISABLE_POSIX_TIMERS)","int","clockid_t","FAR struct sigevent*","FAR timer_t*"
 "timer_delete","time.h","!defined(CONFIG_DISABLE_POSIX_TIMERS)","int","timer_t"

syscall/syscall_funclookup.c

@@ -72,6 +72,7 @@
 #include <signal.h>
 #include <mqueue.h>
 #include <spawn.h>
+#include <termios.h>
 #include <assert.h>
 
 /* Errno access is awkward. We need to generate get_errno() and set_errno()

syscall/syscall_lookup.h

@@ -211,6 +211,9 @@ SYSCALL_LOOKUP(up_assert,                  2, STUB_up_assert)
   SYSCALL_LOOKUP(poll,                     3, STUB_poll)
   SYSCALL_LOOKUP(select,                   5, STUB_select)
 #  endif
+#  ifndef CONFIG_SERIAL_TERMIOS
+  SYSCALL_LOOKUP(tcdrain,                  1, STUB_tcdrain)
+#  endif
 #endif
 
 /* Board support */

syscall/syscall_stublookup.c

@@ -210,6 +210,8 @@ uintptr_t STUB_aio_write(int nbr, uintptr_t parm1);
 uintptr_t STUB_aio_fsync(int nbr, uintptr_t parm1, uintptr_t parm2);
 uintptr_t STUB_aio_cancel(int nbr, uintptr_t parm1, uintptr_t parm2);
 
+uintptr_t STUB_tcdrain(int nbr, uintptr_t parm1);
+
 /* Board support */
 
 uintptr_t STUB_boardctl(int nbr, uintptr_t parm1, uintptr_t parm2);