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Derek Christ
2022-08-15 08:18:13 +02:00
parent faf2842687
commit 9ec2f6f1eb
7 changed files with 30 additions and 30 deletions
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10
inc/3.systemc.tex
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@@ -46,7 +46,7 @@ GPs are passed as references, so they do not need to be copied between modules.
\begin{figure}
\begin{center}
\tikzfig{img/tlm}
\caption[Forward and backward path between TLM sockets \cite{Menard2017}.]{Forward and backward path between TLM sockets \cite{Menard2017}. $\blacksquare$ denotes an initiator socket, $\square$ denotes a target socket.}
\caption[Forward and backward path between TLM sockets.]{Forward and backward path between TLM sockets \cite{Menard2017}. $\blacksquare$ denotes an initiator socket, $\square$ denotes a target socket.}
\label{fig:tlm}
\end{center}
\end{figure}
@@ -67,8 +67,8 @@ With AT, a special protocol is used that uses a four-phase handshake:
When an initiator requests data from a target, it starts the transaction with the \texttt{BEGIN\_REQ} phase by calling its \texttt{nb\_transport\_fw()} method.
This method in turn calls the receiving module's target socket and the target module then enqueues the payload into its \revabbr{payload event queue}{PEQ}.
The PEQ pretends it has received the payload after the delay, that the initiator has specified with its call to the transport method.
If the target is not yet ready to accept a new request, it defers its \texttt{END\_REQ} phase until it is ready.
During this time, the initiator is blocked from sending further requests either to this or other modules as the target applies \textit{backpressure} on the initiator.
If the target is not yet ready to accept the new request, it defers its \texttt{END\_REQ} phase until it is ready.
During this time, the initiator is blocked from sending further requests to this module as the target applies \textit{backpressure} on the initiator.
This concept is called the \textit{exclusion rule}.
Otherwise, the target directly responds the \texttt{END\_REQ} phase back to the initiator.
@@ -94,8 +94,8 @@ Analogously, it is also possible for the initiator to directly respond with the
Besides this, it is also possible for the target to directly respond with the \texttt{BEGIN\_RESP} phase after it has received the \texttt{BEGIN\_REQ} phase and therefore skip the \texttt{END\_REQ}.
The initiator has to react accordingly and must detect that the \texttt{END\_REQ} has been skipped.
However, since the initiator is blocked due to backpressure during this period, this shortcut should only be used if the response is ready to send after a short delay.
Another form of this shortcut is the combination with return path of the forward transport function call.
Here, the return path is used to directly send the \texttt{BEGIN\_REQ} phase, without invoking the backward transport function altogether, reducing the required number of transport calls to only two.
Another form of this shortcut is the combination with the return path of the forward transport function call.
Here, the return path is used to directly send the \texttt{BEGIN\_RESP} phase, without invoking the backward transport function altogether, reducing the required number of transport calls to only two.
The last shortcut that can be made is the so-called \textit{early completion}.
When the target receives the \texttt{BEGIN\_REQ} phase, it can already place the requested data into the payload and pass \texttt{TLM\_COMPLETED} as the return value back to the initiator.