nshterm: add documentation

src/systemcmds/nshterm/nshterm.c

@@ -34,12 +34,10 @@
 
 /**
  * @file nshterm.c
- * start a nsh terminal on a given port. This can be useful for error
- * handling in startup scripts to start a nsh shell on /dev/ttyACM0
- * for diagnostics
  */
 
 #include <px4_config.h>
+#include <px4_module.h>
 #include <termios.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -56,12 +54,25 @@
 
 __EXPORT int nshterm_main(int argc, char *argv[]);
 
+
+static void print_usage(void)
+{
+	PRINT_MODULE_DESCRIPTION("Start an NSH shell on a given port.\n"
+				 "\n"
+				 "This was previously used to start a shell on the USB serial port.\n"
+				 "Now there runs mavlink, and it is possible to use a shell over mavlink.\n"
+				);
+
+	PRINT_MODULE_USAGE_NAME_SIMPLE("nshterm", "command");
+	PRINT_MODULE_USAGE_ARG("<file:dev>", "Device on which to start the shell (eg. /dev/ttyACM0)", false);
+}
+
 int
 nshterm_main(int argc, char *argv[])
 {
 	if (argc < 2) {
-		printf("Usage: nshterm <device>\n");
-		exit(1);
+		print_usage();
+		return 1;
 	}
 
 	unsigned retries = 0;
@@ -90,7 +101,7 @@ nshterm_main(int argc, char *argv[])
 
 			if (armed.armed) {
 				/* this is not an error, but we are done */
-				exit(0);
+				return 0;
 			}
 		}
 
@@ -109,7 +120,7 @@ nshterm_main(int argc, char *argv[])
 
 	if (fd == -1) {
 		perror(argv[1]);
-		exit(1);
+		return 1;
 	}
 
 	/* set up the serial port with output processing */
@@ -146,5 +157,5 @@ nshterm_main(int argc, char *argv[])
 
 	close(fd);
 
-	return OK;
+	return 0;
 }