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68 lines
2.1 KiB
Markdown
68 lines
2.1 KiB
Markdown
# Example 8
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This example is illustrating :
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* The `Duplicate` node to have a one-to-many connection at an output
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* A structured datatype for the samples in the connections
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## Structured datatype
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It is possible to use a custom datatype:
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For the C++ version of the scheduler it would be:
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```python
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complexType=CStructType("MyComplex",8)
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```
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This is defining a new datatype that is mapped to the type `complex` in C/C++.
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The last argument is the size in bytes of the struct in C.
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The type complex may be defined with:
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```c
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typedef struct {
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float re;
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float im;
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} complex;
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```
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For the Python version of the scheduler:
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```python
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complexType=PythonClassType("MyComplex")
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```
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The class `MyComplex` is used in Python.
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**Note that:**
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- The value **must have** value semantic in C/C++. So avoid classes
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- In Python, the classes have reference semantic which implies some constraints:
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- You should never modify an object from the read buffer
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- You should change the field of an object in the write buffer but not the object itself
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- If you need a new object : copy or create a new object. Never use an object from the read buffer as it is if you intend to customize it
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The size of the C structure should take into account the padding that may be added to the struct.
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When no buffer sharing is used, the size of buffers is always expressed in number of samples.
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But in case of buffer sharing, the datatype of the buffer is `int8_t` and the size of the buffer must be computed by the Compute Graph taking into account ay padding that may exist.
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## Duplicate node
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In case of a one-to-many connections, the Python code will automatically add `Duplicate` nodes in the graph. Those `Duplicate` nodes do not appear directly in the graphviz but only as a stylized way : a dot.
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Currently it is limited to 3. If you need more that 3 outputs on an IO you'll have to insert the `Duplicate` nodes explicitly in the graph.
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In the generated code, you'll see the `Duplicate` nodes. For instance, in this example:
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```C++
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Duplicate3<complex,5,complex,5,complex,5,complex,5> dup0(fifo2,fifo3,fifo4,fifo5);
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```
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