CMSIS-DSP/ComputeGraph/documentation/Graph.md

API of the Graph Class

Creating a connection

Those methods must be applied to a graph object created with Graph(). The Graph class is defined inside cmsisdsp.cg.scheduler from the CMSIS-DSP Python wrapper.

def connect(self,input_io,output_io,fifoClass=None,fifoScale = 1.0):

Typically this method is used as:

the_graph = Graph()

# Connect the source output to the processing node input
the_graph.connect(src.o,processing.i)

There are two optional arguments:

• fifoClass : To use a different C++ class for implementing the connection between the two IOs. (it is also possible to change the FIFO class globally by setting an option on the graph. See below). Only the FIFO class is provided by default. Any new implementation must inherit from FIFObase<T>
• fifoScale : In asynchronous mode, it is a scaling factor to increase the length of the FIFO compared to what has been computed by the synchronous approximation. This setting can also be set globally using the scheduler options. fifoScale is overriding the global setting. It must be a float (not an int).

def connectWithDelay(self,input_io,output_io,delay,fifoClass=None,fifoScale=1.0):  

The only difference with the previous function is the delay argument. It could be used like:

the_graph.connect(src.o,processing.i, 10)

The delay is the number of samples contained in the FIFO at start (initialized to zero). The FIFO length (computed by the scheduling) is generally bigger by this amount of sample. The result is that it is delaying the output by delay samples.

It is generally useful when the graph has some loops to make it schedulable.

Options for the graph

Those options needs to be used on the graph object created with Graph().

For instance :

g = Graph()
g.defaultFIFOClass = "FIFO"

defaultFIFOClass (default = "FIFO")

Class used for FIFO by default. Can also be customized for each connection (connect of connectWithDelay call).

duplicateNodeClassName(default="Duplicate")

Prefix used to generate the duplicate node classes like Duplicate2, Duplicate3 ...