pertd2

pertd2 - A daemon that displays information on the Pertelian USB LCD display

Overview

This program creates a fifo and listens to it for commands. The commands can be used to turn the backlight on/off, set the data of each line to display, stop the program, etc.

If the lines are more than the 20 chars allowed for each line, the data is scrolled horizontally.

The data will wrap into unused lines. Ex: if line 1 has data, but line 2 does not, the data from line 1 will wrap into line 2 and both lines will scroll at double speed.

If there is no data to display, the current date/time will display.

The interface to the daemon is through a fifo. The name and location of this fifo is set via a configuration file /etc/pertd2.conf Optionally, you can specify a configuration file on the pertd command line.

The program is set to go daemon right away. So when you run pertd2, you will get a prompt back immediately as it goes off into the background and not be terminated when you log off.

Note that on my system (Mandriva 2007), when the user logs off, ownership of /dev/ttyUSB0 goes back to root. So it's probably a good idea to run this daemon as root. See the service directory for turning pertd2 into a service that runs when the system boots.

Configuration

• delay_time : The interval between screen refreshes in ms. (1000000ms = 1 second) This will basically control how fast the Pertelian scrolls the data across the screen. Default: 500000 (1/2 second)
• char_delay : The delay between each character sent to the Pertelian. This delay prevents the program from sending data too fast and causing garbled output on the display. Newer systems may not need any delay, so I made this configurable. The delay is in ms. 1 ms is usually needed for old systems. If your display is very slow, reduce this to 0. If the output is garbled, put it to 1. Default: 1
• device : The device the Pertelian is on. Default: /dev/ttyUSB0
• fifo_name : The name of the fifo that pertd2 creates.
• backlight_mgt : Backlight management. This indicates whether you want pertd2 to manage the backlight or not. Basically it manages it by turning the backlight on when there is data to display and off when there is no data. 1 = pertd2 manages the backlight. 0 = it doesn't. Default: 0

Commands

backlight on
backlight off
stop
line1
line2
line3
line4
delay time
char delay
backlight mgt on
backlight mgt off

You communicate by sending the command to the fifo. ex: echo "backlight on" > /tmp/pertd2.fifo

Most of the commands should be self-explanatory.

Single line commands:

backlight on
backlight off
stop
backlight mgt on
backlight mgt off

Multiline commands

The "delay time" and "char delay" commands take a second line that specified the value. ex:

delay time
500000

The "line?" commands are a little more complex. ex:

line1
600
==EOD==
The quick brown fox jumped over the lazy dog.
==EOD==

The first line (line1) is the command, also telling pertd2 which line you want this data to go in. The second line (600) is the number of seconds pertd2 should display the data. Basically an expiration time. 0 seconds means "don't expire." The third line is the end of data marker. It will not display. The rest of the lines are the data to be displayed. New lines will be converted to spaces. The data goes from the first EOD marker until it sees another line with the EOD marker, or until it his end of file (i.e. the fifo is empty).

So, you can put these lines into a file:

line1
12
==EOD==
19:26:59
==EOD==
line2
12
==EOD==
Testing
==EOD==

then you can cat file > /tmp/pertd2.fifo to send the commands.

The "sendcommands" directory contains examples of programs that send commands to the fifo.

I release my code into the Public Domain. Have fun, but use this code and the resulting program at your own risk. --Ron Lauzon

2007/03/24 Created by Ron Lauzon