Rodrigo Arias
5d4fa15eb9
Allows mkdocs to discover broken links when the pointed document has moved.
56 lines
2.6 KiB
Markdown
56 lines
2.6 KiB
Markdown
# Mux
|
|
|
|
The emulator provides a mechanism to interconnect [channels](channels.md) in a
|
|
similar way as an [analog
|
|
multiplexer](https://en.wikipedia.org/wiki/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](../user/emulation/nanos6.md):
|
|
|
|
|
|
|
|
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](patchbay.md) allowing the ovni model to
|
|
modify the Nanos6 Paraver view of the subsystems.
|