Lpd provides five attributes which you can set in
/etc/printcap to control all the settings of the serial port
a printer is on. Read the
printcap man
page and note the meanings of br#, fc#,
xc#, fs# and xs#. The last four of these
attributes are bitmaps indicating the settings for use the port. The
br# atrribute is simply the baud rate, ie `br#9600'.
It is very easy to translate from stty settings to printcap flag settings. If you need to, see the man page for stty now.
Use stty to set up the printer port so that you can cat a file to it and have it print correctly. Here's what `stty -a' looks like for my printer port:
dina:/usr/users/andy/work/lpd/lpd# stty -a < /dev/ttyS2
speed 9600 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>;
eol2 = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W;
lnext = ^V; min = 1; time = 0;
-parenb -parodd cs8 hupcl -cstopb cread -clocal -crtscts
-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr
-igncr -icrnl ixon -ixoff -iuclc -ixany -imaxbel
-opost -olcuc -ocrnl -onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0
bs0 vt0 ff0
-isig -icanon -iexten -echo -echoe -echok -echonl -noflsh -xcase
-tostop -echoprt -echoctl -echoke
-clocal, -crtscts, and ixon. Your port may
well be different depending on how your printer does flow control.
You actually use stty in a somewhat odd way. Since stty operates on
the terminal connected to it's standard input, you use it to
manipulate a given serial port by using the `<' character as
above.
Once you have your stty settings right, so that `cat file > /dev/ttyS2' (in my case) sends the file to the printer, look at the file /usr/src/linux/include/asm-i386/termbits.h. This contains a lot of #defines and a few structs (You may wish to cat this file to the printer (you do have that working, right?) and use it as scratch paper). Go to the section that starts out
/* c_cflag bit meaning */
#define CBAUD 0000017
Note which of those settings are preceded with a - in your stty
output. Sum up all those numbers (they are octal). This represents the
bits you want to clear, so the result is your fc# capability. Of
course, remember that you will be setting bits directly after you
clear, so you can just use `fc#0177777' (I do).
Now do the same for those settings (listed in this section) which do
not have a - before them in your stty output. In my example the
important ones are CS8 (0000060), HUPCL (0002000), and CREAD
(0000200). Also note the flags for your baud rate (mine is
0000015). Add those all up, and in my example you get 0002275. This
goes in your fs# capability (`fs#02275' works fine in my
example).
Do the same with set and clear for the next section of the include
file, "c_lflag bits". In my case I didn't have to set anything, so I
just use `xc#0157777' and `xs#0'.
Jon Luckey points out that some older serial printers with ten-cent
serial interfaces and small buffers really mean stop when they
say so with flow control. He found that disabling the FIFO in his
Linux box's 16550 serial port with
setserial
corrected the problem of dropped characters (you apparently just
specify the uart type as an 8250 to do this).