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.

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);