HAL in Measurement Plug-In.md

Creating a HAL for Use in Measurement Plug-ins

• Creating a HAL for Use in Measurement Plug-ins
  • What is HAL?
  • Pre-requisites
  • Steps to implement HAL for a new instrument type
  • Directory structure of HAL
  • Migrate the existing instrument class to Measurement Plug-In
  • Note

What is HAL?

Hardware Abstraction Layer (HAL) enables users to develop applications agnostic of instrument models of a type (like DMM). HAL in measurement plug-ins allows users to work with various instrument models without modifying the implementation. This HAL implementation leverages pins from the pin map.

Pre-requisites

• Fundamental knowledge of HAL.
• Understanding of the session management in the measurement plug-ins.
• Intermediate working experience in Python.

Steps to implement HAL for a new instrument type

1. To implement HAL for a specific instrument type, create a directory to hold the modules related to the HAL implementation.
2. Create a python file named after the instrument type. Example: dmm.py.
3. In the above created file, add an abstract class with the methods that should be called using the instrument session. This module will additionally contain create and destroy methods to initialize and close instrument sessions in the measurement using the TestStand fixture module.
4. Within the root directory create directories for each instrument model. You can refer to the table with directory names for NI and custom instruments in the Note section. Following this, we have named the directories as nidmm and keysightdmm.
5. Each of these directories must have a module with the same name as the directory. The module must have a Session class which inherits and implements the methods from the abstract class created in the root directory.

Directory structure of HAL

1. The recommended directory structure for HAL is shown below:

<hal_root_directory>
   ├── __init__.py
   ├── <instrument_type>.py
   ├── <NI_instrument_type>
   │   └── <NI_instrument_type>.py
   ├── <instrument_model_1>
   │   ├── <instrument_model_1>.py
   │   └── <driver session related files>
   ├── <other instrument model(s)>
   .
   .
   .
   ├── teststand_helper.py
   └── utilities
       └── _visa_grpc.py

Example:

dmm_hal
   ├── __init__.py
   ├── dmm.py
   ├── function.py
   ├── keysightdmm
   │   ├── keysightdmm.py
   │   └── <driver session related files>
   ├── nidmm
   │   └── nidmm.py
   ├── teststand_helper.py
   └── utilities
       └── _visa_grpc.py

Migrate the existing instrument class to Measurement Plug-In

• Create a measurement plug-in by following the steps mentioned in Developing a measurement plug-in with python.
• Copy the existing HAL classes and modules by following the steps from Steps to create a new HAL based measurement to migrate the existing HAL implementation.

Note

1. Directory names for different NI instrument types.

   Instrument type	Directory name
   NI-DCPower	nidcpower
   NI-DMM	nidmm
   NI-Digital Pattern	nidigitalpattern
   NI-SCOPE	niscope
   NI-FGEN	nifgen
   NI-DAQmx	nidaqmx
   NI-SWITCH	nirelaydriver

2. The instrument type id for custom instruments should be a single word, adhering to Python standards. Accordingly, the directories for the instrument models should also be in lowercase. Example: keysightdmm.