2.6 KiB
Mux
The emulator provides a mechanism to interconnect channels in a
similar way as an analog
multiplexer by using the mux
module.
Multiplexers or muxers have one output channel, one select channel and a variable number of input channels (including zero). Each input channel is registered in the multiplexer by using a key with a given value. In the normal operation of a mux, the value of the select channel is used to find an input with a matching key. When there is no match, the output value is set to null.
Multiplexers can be configured to execute a custom select function, which will take the value of the select channel and determine which input should be selected. This allows a multiplexer to act as a filter too.
Tracking
The typical use of multiplexers is to implement the tracking modes of channels. As an example, the following diagram shows two multiplexers used to implement the subsystem view of Nanos6:
The first mux0 selects the input corresponding to the thread running in that CPU (thread0), and forwards the value to the output. If no thread is running the output is set to null. The output channel nanos6.cpu0.subsystem.run is then connected to the Paraver timeline in the row corresponding to the CPU0, which shows the subsystem of the currently running thread.
The Nanos6 subsystem channel is also connected to the second mux1, which forwards the value to the output only when the thread state is Active (not paused or dead). The output is directly connected to the Paraver row assigned to that thread. This view shows the subsystem of the thread when is active.
Notice that when the thread0 is no longer Running (switches to the Cooling state shown in yellow) the CPU subsystem timeline no longer shows the subsystem, as the mux0 is not selecting any input (because there are no threads in the CPU0 in the Running state at that moment).
However, the thread view still shows the subsystem, as the thread0 is still active (not paused yet). The mux1 is still selecting the thread subsystem channel as input.
Separation of concerns
Multiplexers allow models to interact with each other in a controlled way. In the example, the blue channel (nanos6.thread0.subsystem) is directly modified by the Nanos6 model when a new event is received. While the red channels are controlled by the ovni model. The rest of the channels are automatically updated in the propagation phase of the bay allowing the ovni model to modify the Nanos6 Paraver view of the subsystems.