48 lines
2.4 KiB
Markdown
48 lines
2.4 KiB
Markdown
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# Mux
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The emulator provides a mechanism to interconnect [channels](../channels) in a
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similar way as an [analog
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multiplexer](https://en.wikipedia.org/wiki/Multiplexer) by using the `mux`
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module.
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Multiplexers or muxers have one output channel, one select channel and a
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variable number of input channels (including zero). Each input channel is
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registered in the multiplexer by using a key with a given value. In the normal
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operation of a mux, the value of the select channel is used to find an input
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with a matching key. When there is no match, the output value is set to null.
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Multiplexers can be configured to execute a custom select function, which will
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take the value of the select channel and determine which input should be
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selected. This allows a multiplexer to act as a filter too.
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## Tracking
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The typical use of multiplexers is to implement the tracking modes of channels.
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As an example, the following diagram shows three multiplexers used to implement
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the subsystem view of [Nanos6](../nanos6):
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The first mux0 uses the thread state channel to filter the value of the
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subsystem channel and only pass it to the output when the thread is in the
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Running state (green). Then the filtered subsystem channel is connected to an
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input of a second mux (mux1) which selects the current input of the thread
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running in the CPU0. The output *nanos6.cpu.subsystem.run* is then connected to
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the Paraver timeline in the row corresponding to the CPU0, which shows the
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subsystem of the currently running thread.
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The Nanos6 subsystem channel is also connected to the mux2, which forwards the
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value to the output only when the thread state is Active. The output is directly
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connected to the Paraver row assigned to that thread. This channels shows the
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subsystem of the thread by only when is active (not paused nor dead). You can
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see that the subsystem is shown in the thread0 at the current time (red dotted
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line) when in the CPU0 the subsystem has been hidden when the thread stops being
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in the Running state (yellow).
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Multiplexers allow models to interact with each other in a controlled way. In
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the example, the blue channel (*nanos6.thread0.subsystem*) is directly modified by
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the Nanos6 model when a new event is received. While the red channels are
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controled by the ovni model. The rest of the channels are automatically updated
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in the propagation phase of the [bay](../patchbay) allowing the ovni model to
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modify the Nanos6 Paraver view of the subsystems.
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