Use 32 bit Python in 64 bit Redhawk

Question

I am attempting to develop a component for 64 bit Redhawk that uses a 32 bit Python binary, but am not sure how to configure Redhawk use 32 bit Python instead of 64 bit Python when running this particular component. The reason I need to use 32 bit Python is because I am using a library (PyVisa, http://pyvisa.readthedocs.org/en/latest/) that only works with 32 bit Python (see https://decibel.ni.com/content/docs/DOC-2928).

I am using PyVisa to control lab equipment (i.e. Agilent signal generators) in order to a calibrate a receiver. I understand this may seem like a odd use of Redhawk, but tuning sig gens to a certain freq and power level is very similar to operations that need to be performed when controlling a receiver/transmitter as well.

I would rather not install 32 bit CentOS just to develop and test this 1 component and I'm assuming it will be equally troublesome to simultaneously install 32 bit and 64 bit Redhawk rpms on my system.

I have already installed 32 bit Python simultaneously with 64 bit Python on my system and have manually renamed the 32 bit Python binary to be "python_32" and placed it on the path (/usr/bin/). I tried to force Redhawk to use the 32 bit Python executable by changing the shebang at the top of my implementation file to

#!/usr/bin/env python_32

However, it didn't work, so then I tried

#!/usr/bin/python_32

which also didn't work.

See example below for a skeleton implementation, with all the boilerplate imports and function defs removed for clarity.

#!/usr/bin/python_32

import visa
def process(self):
    sg = visa.instrument("TCPIP::10.2.8.236")
    print sg.ask("*IDN?")
    return NORMAL

Each time I attempt to launch a simple waveform containing this component, I receive the error below. This is the same error I receive when trying to use the PyVisa libary in 64 bit Python, which is why I think Redhawk is ignoring my shebang statements specifying the path to 32 bit Python.

OSError: /usr/local/vxipnp/linux/bin/libvisa.so.7: wrong ELF class: ELFCLASS32
Traceback (most recent call last):
  File "/var/redhawk/sdr/dev/.DevMgr_orion/GPP_orion/components/sendSCPI/python/sendSCPI.py", line 9, in <module>
    import visa
  File "/usr/lib/python2.6/site-packages/PyVISA-1.5.dev0.dev-py2.6.egg/visa.py", line 237, in <module>
    resource_manager = ResourceManager()
  File "/usr/lib/python2.6/site-packages/PyVISA-1.5.dev0.dev-py2.6.egg/vpp43.py", line 85, in __new__
    it.init(*args, **kwds)
  File "/usr/lib/python2.6/site-packages/PyVISA-1.5.dev0.dev-py2.6.egg/visa.py", line 230, in init
    self.session = self.vi = vpp43.open_default_resource_manager()
  File "/usr/lib/python2.6/site-packages/PyVISA-1.5.dev0.dev-py2.6.egg/vpp43.py", line 788, in open_default_resource_manager
    visa_library().viOpenDefaultRM(byref(session))
  File "/usr/lib/python2.6/site-packages/PyVISA-1.5.dev0.dev-py2.6.egg/vpp43.py", line 162, in __call__
    self.load_library()
  File "/usr/lib/python2.6/site-packages/PyVISA-1.5.dev0.dev-py2.6.egg/vpp43.py", line 131, in load_library
    self.__lib = self.__cdecl_lib = cdll.LoadLibrary(path)
  File "/usr/lib64/python2.6/ctypes/__init__.py", line 431, in LoadLibrary
    return self._dlltype(name)
  File "/usr/lib64/python2.6/ctypes/__init__.py", line 353, in __init__
    self._handle = _dlopen(self._name, mode)
OSError: /usr/local/vxipnp/linux/bin/libvisa.so.7: wrong ELF class: ELFCLASS32

For reference I am running Redhawk version 1.9.0. x64 on CentOS 6.4 x64.

If there is a better way to control my lab equipment through Redhawk, I'm open to that too.

Answer 1

The <entrypoint> in the component.spd.xml file can be changed to point to a script instead of the component's .py file. This is useful for doing things like setting environment variables for a single component or redirecting to a different program.

Consider this:

1. Change <entrypoint>python/myComponent.py</entrypoint> to <entrypoint>python/myScript.sh</entrypoint>

2. Create a script called myScript.sh in the python folder.

3. Populate myScript.sh with something like:

   export PYTHONPATH=$PYTHONPATH # add/change PYTHONPATH (or other environment variables) here

   /usr/bin/python_32 python/myComponent.py $*

4. chmod +x myScript.sh

5. Modify your autotools files so that the script gets installed correctly (or just copy it by hand)

This approach gives you a little more control over how myComponent.py gets run.