= Halui Examples

For any Halui examples to work you need to add the following line to the \[HAL\] section of the ini file.

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+*HALUI = halui*+ 

== Remote Start

To connect a remote program start button to LinuxCNC you use the 
`halui.program.run` pin and the `halui.mode.auto` pin. 
You have to insure that it is OK to run first by using the 
`halui.mode.is-auto` pin. You do this with an `and2` 
component. The following figure shows how this is done. 
When the Remote Run Button is pressed it is connected to 
both `halui.mode.auto` and `and2.0.in0`. If it is OK for 
auto mode the pin `halui.mode.is-auto` will be on. 
If both the inputs to the `and2.0` component are on the 
`and2.0.out` will be on and this will start the program. 

[[fig:Remote-Start-Example]]
.Remote Start Example

image::images/remote-start.png[]

The hal commands needed to accomplish the above are: 

    net program-start-btn halui.mode.auto and2.0.in0 <= <your input pin> 
    net program-run-ok and2.0.in1 <= halui.mode.is-auto 
    net remote-program-run halui.program.run <= and2.0.out 

Notice on line one that there are two reader pins, this can also be split up to two lines like this:

    net program-start-btn halui.mode.auto <= <your input pin> 
    net program-start-btn and2.0.in0 

== Pause & Resume

This example was developed to allow LinuxCNC to move a 
rotary axis on a signal from an external machine. 
The coordination between the two systems will be 
provided by two Halui components: 

 - halui.program.is-paused
 - halui.program.resume

In your customized hal file, add the following 
two lines that will be connected to your I/O to turn 
on the program pause or to resume when the external 
system wants LinuxCNC to continue. 

    net ispaused halui.program.is paused => "your output pin" 
    net resume halui.program.resume <= "your input pin" 

Your input and output pins are connected to the pins 
wired to the other controller. They may be parallel port 
pins or any other I/O pins that you have access to. 

This system works in the following way. When an M0 is 
encountered in your G-code, the `halui.program.is-paused` 
signal goes true. This turns on your output pin so that 
the external controller knows that LinuxCNC is paused. 

To resume the LinuxCNC gcode program, when the external controller 
is ready it will make its output true. This will signal 
LinuxCNC that it should resume executing Gcode. 

Difficulties in timing

 - The "resume" input return signal should not be 
   longer than the time required to get the g-code 
   running again. 

 - The "is-paused" output should no longer be active 
   by the time the "resume" signal ends. 

These timing problems could be avoided by using
ClassicLadder to activate the "is-paused" output via a 
monostable timer to deliver one narrow output pulse. 
The "resume" pulse could also be received via a monostable timer.