[ECOS] tty driver

["Perry Wang" <perrywang at nmnc dot com>]

The current tty driver source echos backspace even if it's already at the
beginning of the line.

Also, cyg_io_read returns -1 when user send backspace at the beginning of
the line.  This is self-explanatory if you look at the code.

Here is the fix.  Please let me know if all this is unnecessary.  I would
prefer not having to change the eCos source.


--------------


[root@mail common]# diff -u tty.c.orig tty.c
--- tty.c.orig  Tue Dec 21 14:17:14 1999
+++ tty.c       Tue Dec 21 14:44:19 1999
@@ -191,7 +191,8 @@
     cyg_devtab_entry_t *t = (cyg_devtab_entry_t *)handle;
     struct tty_private_info *priv = (struct tty_private_info *)t->priv;
     cyg_io_handle_t chan = (cyg_io_handle_t)priv->dev_handle;
-    cyg_uint32 size, clen;
+    cyg_int32 size;
+    cyg_uint32 clen;
     Cyg_ErrNo res;
     cyg_uint8 c;
     cyg_uint8 *buf = (cyg_uint8 *)_buf;
@@ -208,8 +209,11 @@
         if ((priv->dev_info.tty_in_flags & CYG_TTY_IN_FLAGS_BINARY) == 0) {
             if ((c == '\b') || (c == 0x7F)) {
                 size -= 2;  // erase one character + 'backspace' char
-                if (size < 0) size = 0;
-                if (priv->dev_info.tty_in_flags & CYG_TTY_IN_FLAGS_ECHO) {
+                if (size < 0) {  // beginning of the line, don't echo \b
+                    size = 0;
+                } else if (priv->dev_info.tty_in_flags &
+                           CYG_TTY_IN_FLAGS_ECHO)
+                {
                     clen = 3;
                     cyg_io_write(chan, "\b \b", &clen);
                 }