[LinuxCNC/linuxcnc Issue#621] hal.get_value() should not require the creation of a component

Here are the steps I follow to reproduce the issue:

1. In a standalone Python script call hal.get_value() without creating a component

I am running a standalone Python script for probing – invoked manually from the terminal. My understanding of hal.getvalue() is that it can be used to get the value of any pin, param or signal not only those coming from a userspace component. In fact it does work if I first create a dummy component. The request is that hal.getvalue() should not require the creation of a component.

h = hal.component(“dummy”)
h.ready()
…
if hal.get_value(‘motion.probe-input’):
print(‘Probe is tripped – is the probe plugged in?’)
return -1

This is what I expected to happen:

I expected hal.get_value() to return the value of the pin.

This is what happened instead:

An error message was returned:

RuntimeError: Cannot call before creating component

Information about my hardware and software:

* I am using this Linux distribution and version (often, shown by lsb_release -a):
Linux Mint 19.1 Tessa
* I am using this kernel version (shown by uname -a):
Linux platform 4.19.1-rt3 #1 SMP PREEMPT RT Sat Mar 2 19:53:32 EST 2019
* I am running …
* [ ] A binary version from linuxcnc.org (including buildbot.linuxcnc.org)
* [x] A binary I built myself
* [ ] A binary version from some other source besides linuxcnc.org
* I am using this LinuxCNC version (shown in package manager or, for git versions, scripts/get-version-from-git):
Branch 2.8, last built I think June 25
* I am using this user interface (GUI) (e.g., AXIS, Touchy, gmoccapy, etc):
AXIS
* I am using this interface hardware vendor and chipset (e.g., parallel port, ethernet port, FPGA card):
Mesa 5i25