Changes between Version 16 and Version 17 of serial

Timestamp:

09/05/2019 12:29:37 AM (5 years ago)

Author:

Tim Harvey

Comment:

added section about serial console

serial

@@ -663 +663 @@
 
 
+
+
+[=#console]
+= Serial Console
+
+== Serial Console Window Size
+console applications running inside Linux virtual terminal applications (xterm, rxvt etc) will receive SIGWINCH after a resize operation has taken place and adjust accordingly.
+
+When using a serial console there is no such mechanism and you can see the affect of this by connecting to a serial console (ie jtag_com/jtag_gang) and showing your size either via env vars or via the 'stty size' app:
+{{{#!bash
+~# echo $LINES $COLUMNS
+24 80
+~# stty size
+24 80
+}}}
+
+No matter how you resize that virtual terminal window (ie xterm), the above commands will always report the same size.
+
+It is possible for the application to actively ask for the current console window size so the second best thing is to do this every time a command prompt is printed by the shell. This can be achieved by sending a ANSI code to position the cursor to 999,999 then request the cursor position.
+
+The 'resize' app from the 'xterm' package does this, but here is also a cleaner version with less dependencies:
+{{{#!bash
+wget http://web.archive.org/web/20081224152013/http://www.davehylands.com/gumstix-wiki/resize/resize.c
+gcc resize.c -o /usr/local/bin/resize
+}}}
+
+You can also do this with shell scripts that do the same thing:
+{{{#!bash
+resize() {
+  old=$(stty -g)
+  stty raw -echo min 0 time 5
+  printf '\0337\033[r\033[999;999H\033[6n\0338' > /dev/tty
+  IFS='[;R' read -r _ rows cols _ < /dev/tty
+  stty "$old"
+  #echo "size:${cols}x${rows}"
+  stty cols "$cols" rows "$rows"
+}
+}}}
+
+you could add this and the following to your /etc/bash.bashrc:
+{{{#!bash
+[[ "$(tty)" =~ "/dev/ttymxc" ]] && { resize; }
+}}}
+
+some people also opt to use the 'trap' shell function to execute it on every command:
+{{{#!bash
+[[ "$(tty)" =~ "/dev/ttymxc" ]] && { trap resize DEBUG; }
+}}}
+
+Notes:
+ - 'tty' shows the name of the terminal device (ie /dev/ttymxc1 if on a Ventana serial console)
+ - 'stty size' outputs the current terminal size based on what the kernel thinks
+ - this has nothing to do with terminal type (TERM)
+ - when remotely connected to a board via ssh for example, this isn't an issue as that can use SIGWINCH
+orts 24 80
+ - the COLUMNS and LINES env variables reflect the size of the tty
+ - resizable terminals are the result of NAWS 'Negotiate About Window Size' from RFC 1073 Telnet Window Size Option
+
+References:
+- https://unix.stackexchange.com/questions/16578/resizable-serial-console-window
+- http://web.archive.org/web/20081224152013/http://www.davehylands.com/gumstix-wiki/resize/resize.c
+{{{#!c
+/* resize.c */
+
+#include <stdio.h>
+#include <ctype.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <string.h>
+#include <termio.h>
+#include <termios.h>
+
+
+#include <signal.h>
+#include <pwd.h>
+
+#define ESC "\033"
+
+
+#define TIMEOUT         10
+
+
+char *myname;
+
+char getsize[] = ESC "7"  ESC "[r" ESC "[999;999H" ESC "[6n";
+char restore[] = ESC "8";
+
+struct termios tioorig;
+
+char size[] = ESC "[%d;%dR";
+
+int tty;
+FILE *ttyfp;
+
+static void onintr (int sig);
+static void resize_timeout (int sig);
+static void Usage (void);
+static void readstring (FILE *fp, char *buf, char *str);
+
+char *
+x_basename(char *name)
+{
+   char *cp;
+
+   cp = strrchr(name, '/');
+   return (cp ? cp + 1 : name);
+}
+
+
+/*
+  tells tty driver to reflect current screen size
+ */
+
+int
+main (int argc, char **argv)
+{
+
+       int rows, cols;
+       struct termios tio;
+       char buf[BUFSIZ];
+       struct winsize ws;
+       char *name_of_tty;
+
+       myname = x_basename(argv[0]);
+
+       if (argc > 1) Usage();
+
+       name_of_tty = "/dev/tty";
+
+       if ((ttyfp = fopen (name_of_tty, "r+")) == NULL) {
+           fprintf (stderr, "%s:  can't open terminal %s\n",
+                    myname, name_of_tty);
+           exit (1);
+       }
+       tty = fileno(ttyfp);
+
+       tcgetattr(tty, &tioorig);
+       tio = tioorig;
+       tio.c_iflag &= ~ICRNL;
+       tio.c_lflag &= ~(ICANON | ECHO);
+       tio.c_cflag |= CS8;
+       tio.c_cc[VMIN] = 6;
+       tio.c_cc[VTIME] = 1;
+       signal(SIGINT, onintr);
+       signal(SIGQUIT, onintr);
+       signal(SIGTERM, onintr);
+       tcsetattr(tty, TCSADRAIN, &tio);
+
+       write(tty, getsize, strlen(getsize));
+       readstring(ttyfp, buf, size);
+       if(sscanf (buf, size, &rows, &cols) != 2) {
+               fprintf(stderr, "%s: Can't get rows and columns\r\n", myname);
+               onintr(0);
+       }
+       write(tty, restore, strlen(restore));
+
+       if (ioctl (tty, TIOCGWINSZ, &ws) != -1) {
+           /* we don't have any way of directly finding out
+              the current height & width of the window in pixels.  We try
+              our best by computing the font height and width from the "old"
+              struct winsize values, and multiplying by these ratios...*/
+           if (ws.ws_col != 0)
+               ws.ws_xpixel = cols * (ws.ws_xpixel / ws.ws_col);
+           if (ws.ws_row != 0)
+               ws.ws_ypixel = rows * (ws.ws_ypixel / ws.ws_row);
+           ws.ws_row = rows;
+           ws.ws_col = cols;
+           ioctl (tty, TIOCSWINSZ, &ws);
+       }
+
+       tcsetattr(tty, TCSADRAIN, &tioorig);
+       signal(SIGINT, SIG_DFL);
+       signal(SIGQUIT, SIG_DFL);
+       signal(SIGTERM, SIG_DFL);
+
+       exit(0);
+}
+
+
+static void
+readstring(register FILE *fp, register char *buf, char *str)
+{
+       register int last, c;
+
+       signal(SIGALRM, resize_timeout);
+       alarm (TIMEOUT);
+       if ((c = getc(fp)) == 0233) {   /* meta-escape, CSI */
+               *buf++ = c = ESC[0];
+               *buf++ = '[';
+       } else {
+               *buf++ = c;
+       }
+       if(c != *str) {
+               fprintf(stderr, "%s: unknown character, exiting.\r\n", myname);
+               onintr(0);
+       }
+       last = str[strlen(str) - 1];
+       while((*buf++ = getc(fp)) != last)
+           ;
+       alarm (0);
+       *buf = 0;
+}
+
+static void
+Usage(void)
+{
+       fprintf(stderr,
+        "Usage: %s\n"
+        "   sets size via ioctl\n", myname);
+       exit(1);
+}
+
+static void
+resize_timeout(int sig)
+{
+       fprintf(stderr, "\n%s: timeout occurred\r\n", myname);
+       onintr(sig);
+}
+
+/* ARGSUSED */
+static void
+onintr(int sig)
+{
+       tcsetattr (tty, TCSADRAIN, &tioorig);
+       exit(1);
+}
+
+}}}