--- /dev/null
+The billboard block is designed to help embedding external data directly into the read-out data stream.
+The module consists of a 256x4b memory area that can be randomly accessed via slow-control and a trigger unit that controls how often data is sent.
+
+\subsection{Trigger Scheme}
+ In order to reduce the band-width, the module can skip certain triggers; by default it is completely inactive.
+ There are two methods to select a trigger, namely time-based and trigger-type-based.
+ A combination of both concepts allows you, for instance, to send data at each status trigger, at each 1000th physics trigger, but at-least once every 10~ms.
+ Of course, a time-based read-out only happens, if the CTS issues a trigger.
+
+ If either of the following two sub-modules fires, data is written into the stream (this is called an active event):
+ \begin{enumerate}
+ \item
+ \textbf{Time-Based}:
+ The \texttt{TimeThresholdReg} registers allows you to define a time interval between two active event.
+ If a read-out happened, all events within this window are ignored for the time-based decision.
+ The first event to arrive after the threshold is selected and triggers a read-out.
+ The counter is reset by any active event.
+ Set the threshold register to 0 (default) to prevent any time-based decision.
+
+ \item
+ \textbf{Trigger-Type Thinning}:
+ For each trigger type $i$ there exists a so called skip register $i$.
+ It specifies the number of triggers of this type to be ignored between two active read-out.
+ Consider the physics trigger type 1 and let $x$ be the value of the corresponding register:
+ The first physics trigger received invokes an active read-out, while the next $x$ physics trigger are ignored.
+ The subsequent trigger then becomes active again (and so on).
+ Time-based decisions from other trigger types do not interfere with this pattern.
+ \end{enumerate}
+
+\subsection{Memory}
+ The memory is directly mapped into the slow-control address space and is randomly accessible.
+ The module employs a shadow-memory to prevent data corruption in case a read-out occurs while you update the data.
+ This, however, happens fully transparent and is not resembled on the slow-control addresses.
+
+ Once you have written all values into the memory, you can \emph{commit} the data by writing its length into \texttt{CommitReg}.
+ In the next active event, the module will send the number of words specified whilst committing into the read-out stream, starting at the lowest memory address.
+ Due to the shadow memory, you cannot reuse unchanged parts of the data, but have to write the whole block, before commit.
+ \textbf{Do not assume any initial value!}
+
+ \emph{Note:} In theory it can happen, that you commit while a read-out takes place.
+ In this case, the new memory block is directly accessible (even if it is still used by the read-out).
+ However, the module will stall writes to addresses, that are not sent yet.
+ This may lead to a time-out error for the write-command via slow-control.
+ In this case, simply write it again.
+ The odds for this to happen are very small and it will never occur if you start writing at the lowest address.
+
+\subsection{Slow Control}
+ {\small
+\begin{longtable}
+{ p{4cm} l c p{8cm} }
+\toprule
+ \textbf{Register} & \textbf{Addr} & \textbf{Bits} & \textbf{Description} \\
+\midrule
+\midrule
+\endfirsthead\multicolumn{4}{c}{\tablename\ \thetable\ -- \textit{Continued from previous page}} \\\toprule
+ \textbf{Register} & \textbf{Addr} & \textbf{Bits} & \textbf{Description} \\
+\midrule
+\midrule
+\endhead\multicolumn{4}{r}{\textit{Continued on next page}} \\
+ \endfoot
+ \endlastfoot \textbf{CommitReg}\hfill(rw) & b000 & & When reading: Length of data block used for current read-out, When writing: Commit data in memory and set length of data \\
+ \quad CommitLength & & 0--7 & Length of data in 32-bit words \\
+\rowcolor{light-gray}
+ \textbf{TimeThresholdReg}\hfill(rw) & b001 & & Time-Out used for time-based trigger decision (Once a read-out happened use first trigger after at least the time specified) \\
+\rowcolor{light-gray}
+ \quad TimeThreshold & & 0--31 & 0: Disable timing-based decision, otherwise: Minimal time between two events in TrbNet clock cycles \\
+ \textbf{FramesSentReg}\hfill(r) & b002 & 0--31 & Statistics: Number of triggers with active read-out (frames sent) \\
+\rowcolor{light-gray}
+ \textbf{WordsSentReg}\hfill(r) & b003 & 0--31 & Statistics: Number of words sent (incl. header) \\
+ \textbf{NumberCommitsReg}\hfill(r) & b004 & 0--31 & Statistics: Number of commits issued \\
+\rowcolor{light-gray}
+ \textbf{AgeLastCommitReg}\hfill(r) & b005 & 0--31 & TrbNet clock cycles since last commit \\
+ \textbf{SkipTriggerReg.0}\hfill(rw) & b010 & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+\rowcolor{light-gray}
+ \textbf{SkipTriggerReg.1}\hfill(rw) & b011 & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+ \textbf{SkipTriggerReg.2}\hfill(rw) & b012 & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+\rowcolor{light-gray}
+ \textbf{SkipTriggerReg.3}\hfill(rw) & b013 & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+ \textbf{SkipTriggerReg.4}\hfill(rw) & b014 & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+\rowcolor{light-gray}
+ \textbf{SkipTriggerReg.5}\hfill(rw) & b015 & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+ \textbf{SkipTriggerReg.6}\hfill(rw) & b016 & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+\rowcolor{light-gray}
+ \textbf{SkipTriggerReg.7}\hfill(rw) & b017 & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+ \textbf{SkipTriggerReg.8}\hfill(rw) & b018 & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+\rowcolor{light-gray}
+ \textbf{SkipTriggerReg.9}\hfill(rw) & b019 & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+ \textbf{SkipTriggerReg.10}\hfill(rw) & b01a & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+\rowcolor{light-gray}
+ \textbf{SkipTriggerReg.11}\hfill(rw) & b01b & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+ \textbf{SkipTriggerReg.12}\hfill(rw) & b01c & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+\rowcolor{light-gray}
+ \textbf{SkipTriggerReg.13}\hfill(rw) & b01d & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+ \textbf{SkipTriggerReg.14}\hfill(rw) & b01e & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+\rowcolor{light-gray}
+ \textbf{SkipTriggerReg.15}\hfill(rw) & b01f & 0--31 & Number of event of trigger type addr[3:0] to be skipped \\
+\bottomrule
+\caption{Registers in group StatusAndControl}\label{tab:BillboardStatusAndControl}\end{longtable}
+}
+
+\subsection{SubSubEvent Format}
+ The read-out data-stream starts with a header word, that is present even if no data follows.
+ If the event is active, memory words 0 to $n$ follow, where $n$ is the length specified when commiting.
+ In case of an inactive event, the length indicator still shows $n$ but the ActiveEvent-bit is 0.
+ This allows you to check, whether the slow-control update have been successful.
+
+ {\small
+\begin{longtable}
+{ p{4cm} c p{8cm} }
+\toprule
+ \textbf{Register} & \textbf{Bits} & \textbf{Description} \\
+\midrule
+\midrule
+\endfirsthead\multicolumn{3}{c}{\tablename\ \thetable\ -- \textit{Continued from previous page}} \\\toprule
+ \textbf{Register} & \textbf{Bits} & \textbf{Description} \\
+\midrule
+\midrule
+\endhead\multicolumn{3}{r}{\textit{Continued on next page}} \\
+ \endfoot
+ \endlastfoot
+ \textbf{ReadoutHeader} & & First word of data-stream \\
+ \quad CommitLength & 0--11 & Number of data (in 32-bit words) committed \\
+ \quad NumberCommits & 12--15 & Lower bits of the NumberCommits statistics counter \\
+ \quad CommitAge & 16--30 & Age of commit in 1.31~ms \\
+ \quad ActiveEvent & 31 & 0: No data follows \\
+ & & 1: Amount specified in CommitLength follows \\
+\bottomrule
+\caption{Readout Header}\label{tab:BillboardReadoutHeader}\end{longtable}
+}
+
+
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