Python bindings for Basler's VisualApplets TCL script generation

Jürgen Hock

Last update: Dec 7, 2022

Related tags

Miscellaneous python design fpga algorithms dsp scripting tcl prototyping xilinx machine-vision data-processing silicon basler siso visualapplets

Overview

About visualapplets.py

The Basler AG company provides a TCL scripting engine to automatize the creation of VisualApplets designs (a former Silicon Software GmbH technology), which is a nice and useful feature but not nice enough, in my opinion.

The main idea of the visualapplets.py project is to introduce an additional scripting abstraction and to script the creation of TCL scripts via Python.

Huh, to script a script? Too much meta? Let's study an example...

Example

In this example we will implement the ReLU operator, which functionally corresponds to y(x) = max(0, x).

Just for practical reasons, we encapsulate the operator logic in a HierarchicalBox. So it can be reused many times in a VisualApplets design. Consequently we also create a class in our Python script, for the same purpose of course.

We begin with the first part of the Python script example.py:

import visualapplets as VA

class Example(VA.Module):

    def __init__(self, parent, name, x, y):

        # initialize the HierarchicalBox (e.g. super)
        super().__init__('HierarchicalBox', parent, name, i=1, o=1, x=x, y=y)

        # create required modules inside the HierarchicalBox (e.g. self)
        branch = VA.Module('BRANCH', self, 'Branch', o=3, x=1, y=1)
        condition = VA.Module('IS_GreaterThan', self, 'Condition', x=2, y=2)
        value = VA.Module('CONST', self, 'Value', x=2, y=3)
        decision = VA.Module('IF', self, 'Decision', x=3, y=1)

        # link created modules together, from left to right
        self('INBOUND') - branch
        branch(0) - decision('I')
        branch(1) - condition - decision('C')
        branch(2) - value - decision('E')
        decision - self('OUTBOUND')

        # for instance, set desired link properties
        branch('I')['Bit Width'] = 16        # input link of the BRANCH
        branch('I')['Arithmetic'] = 'signed'
        value('O')['Bit Width'] = 16         # output link of the CONST
        value('O')['Arithmetic'] = 'signed'  # (needs to match the input link)

        # for instance, set desired module properties
        condition['Number'] = 0  # input value threshold
        value['Value'] = 0       # output value below threshold

Now the second part of our Python script:

# dump generated TCL script to a file instead of stdout
VA.printer = VA.FilePrinter('example.tcl')

# create a design with an instance of the example module
design = VA.Design('mE5-MA-VCLx', 'Example')
example = Example(design, 'Example', x=1, y=2)

Finally import the generated example.tcl file in the VisualApplets IDE or execute something like this in the TCL console:

CloseDesign Discard
source "C:/foo/bar/example.tcl"

The resulting design should look similar to this one:

Basics

With the help of the previous example imagine now, how custom algorithms could be implemented without a deep TCL knowledge, but of course not without a certain amount of Python experience.

There are a few basic concepts to understand how the visualapplets.py works.