An optional ``shutter'' can be enabled. When the shutter is ``closed'' triggers are vetoed and no triggers are sent. When the shutter is ``open'' triggers can be generated and sent to active DUTs.
The shutter cycle can either be started by an external signal or synchronized by a counter clocked by the system clock.
The external signal, if used, must be connected to one of the trigger inputs. An appropriate threshold should be set and the input used for synchronizing the shutter should not be used in the trigger mask.
Figure \ref{fig:shutter_timing} illustrates the timing of the shutter. Behaviour of the shutter is controlled by the IPBus registers described in table \ref{tab:shutter_registers}.
\begin{table}
\begin{tabular}{lp{\0.6\linewidth}}
Register Name & Function \\\hline
ControlRW & Bit-0 controls if shutter pulses are active. 1 = active. Bit-1 selects external synchronization (bit-1 = 0) or internal sequence (bit-1 = 1) \\
ShutterSelectRW & Selects which input is used to trigger shutter sequence.range = 0-5)\\
InternalShutterPeriodRW & Internal sequence period (when using internal sequence). Units of clock cycles.\\
ShutterOnTimeRW & Time between start of sequence and shutter asserted( t1) \\
ShutterVetoOffTimeRW & time between start of sequence and veto being de-asserted (t2)\\
ShutterOffTimeRW & Time between start of sequence and time at which shutter de-asserted and veto reasserted (t3) \\
\end{tabular}
\caption{IPBus registers controlling behaviour of shutter.}
\label{tab:shutter_registers}
\end{table}
An optional ``shutter'' can be enabled. When the shutter is ``closed'' triggers are vetoed and no triggers are sent. When the shutter is ``open'' triggers can be generated and sent to active DUTs.\\
The shutter cycle can either be started by an external signal or synchronized by a counter clocked by the system clock.\\
The external signal, if used, must be connected to one of the trigger inputs (i.e. of the the six the LEMO inputs).\\
\begin{alertinfo}{If the external signal is used, an appropriate threshold should be set to the corresponding input. The input used for synchronizing the shutter should not be used in the trigger mask.}
\end{alertinfo}
Figure~\ref{fig:shutter_timing} illustrates the timing of the shutter.\\
Behaviour of the shutter is controlled by the IPBus registers that can be configured using the configuration parameters described in table~\ref{tab:shutter_registers}.
EnableShutterMode &\begin{tabular}[c]{@{}l@{}}If 1, shutter mode is enabled.\\ If 0, shutter mode is disabled.\end{tabular}&& ControlRW \\\hline
ShutterSource & Selects which input is used to trigger shutter sequence. & Range 0:5 & ShutterSelectRW \\\hline
InternalShutterInterval &\begin{tabular}[c]{@{}l@{}}Internal shutter period when using internal sequence.\\ Set to 0 to not use internal shutter generator.\end{tabular}&\begin{tabular}[c]{@{}l@{}}32-bit vale.\\ Units of 25 ns clock cycles.\end{tabular}& InternalShutterPeriodRW \\\hline
ShutterOnTime & Time between start of sequence and shutter asserted (t$_{1}$) &\begin{tabular}[c]{@{}l@{}}32-bit vale.\\ Units of 25 ns clock cycles.\end{tabular}& ShutterOnTimeRW \\\hline
ShutterVetoOffTime & Time between start of sequence and veto being de-asserted (t$_{2}$) &\begin{tabular}[c]{@{}l@{}}32-bit vale.\\ Units of 25 ns clock cycles.\end{tabular}& ShutterVetoOffTimeRW \\\hline
ShutterOffTime &\begin{tabular}[c]{@{}l@{}}Time between start of sequence and time at which\\ shutter de-asserted and veto reasserted (t$_{3}$)\end{tabular}&\begin{tabular}[c]{@{}l@{}}32-bit vale.\\ Units of 25 ns clock cycles.\end{tabular}& ShutterOffTimeRW \\\hline
\end{tabular}
\caption{Configuration parameters and corresponding IPBus registers controlling behaviour of shutter.}
