wago access

This program runs on a Wago Linux controller. Its job is to export the external inputs and outputs in a controlled fashion.

It implements the following features (in parentheses: the commands in question; no command means TODO):

• read inputs (i)
• read and write outputs (s c I)
• set or clear an output for a pre-set time (s c)
• periodically set+clear an output (Pulse Width Modulation) (s c)
• send a notification whenever an input changes (m+)
• count input transitions, with report timer (i.e. don't send a network message at every transition) (m#)

as well as some auxiliary functions

• measure controller's cycle time (dc)
• set program's poll time (d)
• (re)initialize outputs, in case of network outage
• keepalive messages and timer (m)
• report the kernel-exported CSV list of I/O fields (D)

The controller has a 3 msec debounce filter on its input. The minimum sensible cycle time therefore is 2 msec. If you know that no input will change faster than once a second, increasing the timer values will save some power and allow the program to react faster (since it usually doesn't need to wait for the controller to finish processing its input+output list).

There can be more than one active server connection. Monitors, re-inits and keepalives are specific to the connection they have been issued on.

TODO: A challenge/response mechanism is used to authorize the remote side.

Building and installing

This program depends on uClibc and libevent2.

uClibc is available from Wago.

For libevent2, download the source and configure as

sh configure LDFLAGS=-Wl,-elf2flt CC=/usr/local/bin/arm-uclinux-elf-gcc --host=arm-uclinux-elf --disable-openssl --disable-thread-support --disable-malloc-replacement --disable-shared --prefix=/usr/local/arm-linux-uclibc/

The line protocol

The interface to the daemon consists of a simple command/response protocol.

Commands are single letters. They might have arguments.

Responses are each introduced with a single special character:

• A spontaneous one-line message, not in response to a command.

• a single-line positive response. Depending on the command, it may include data.

? A single-line negative response, indicating an error.

= a multi-line response, terminated by a single dot. (cf. SMTP.)

Used primarily for help messages.

The following messages contain a monitor number after the initial character(s).

!+ a monitor has been created.

! a signal from a monitor. Parameters depend on the type of signal requested.

!- the monitor has been cleared.

Commands

Use 'h' for basic help, and a command list.

Use 'hX' for basic help, and a command list.