source: firmware/FTM/doc/v4.3/FTM_firmware_specs_v4-3.tex@ 10993

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\title{\vspace*{-7cm} \Huge \bf FTM Firmware Specifications}
\author{\Large Patrick Vogler\footnote{Contact for questions and suggestions concerning this
    document: {\tt patrick.vogler@phys.ethz.ch}}, Quirin Weitzel}
\date{\vspace*{0.5cm} \Large v4.3~~~-~~~May 2011}

\begin{document}

\maketitle

\newpage

\tableofcontents

%---------------------------------------------------------------------------------

\chapter{Introduction}
\label{cha:Introduction}

The FTM (FACT Trigger Master) board collects the trigger primitives from all
40 FTU boards (FACT Trigger Unit) and generates the trigger signal for the
FACT camera. The trigger logic is a 'n-out-of-40' majority coincidence of all
trigger primitives. Beside the trigger, the FTM board also generates a
trigger-ID (see chapter \ref{cha:Trigger-ID}). It is controlled from outside
via ethernet. Two auxiliary RS-485 interfaces are also available.

In addition to the trigger, the FTM board also generates other fast control
signals: Time-Marker (TIM), DRS \cite{DRS4} reference clock (CLD) and
reset. These four fast control signals are distributed to the FAD (FACT Analog
to Digital) boards via two FFC (FACT Fast Control) boards. The FTM board also
provides via the TIM line the signal for the DRS timing calibration. In order
to generate the CLD DRS reference clock, as well as the time-marker signal for
DRS timing calibration, the FTM board uses a clock conditioner
\cite{LMK03000}.

The FTM board has two time counters, the 'timestamp counter' and the 'on-time
counter'. While the 'timestamp counter' runs continuously, the 'on-time
counter' only counts when the camera trigger is enabled.

The FTM board further serves as slow control master for the 40 FTU boards. The
slow control of the FTU boards and the distribution of the trigger-ID to the
FAD boards are performed via dedicated RS-485 buses. Because the FAD as well
as the FTU boards are arranged in crates of 10 boards each, the FTM board has
four connectors, one for each crate. Running over these connectors there are
two RS-485 buses (one for FTU slow control and one for the trigger-ID) besides
the busy signal from the FAD boards and the crate reset.

In addition, the FTM board controls the two FLPs (FACT Light Pulser) via four
LVDS signals each. Light pulser~1 is located in the mirror dish, light
pulser~2 inside the camera shutter. There are also digital auxiliary in- and
outputs according to the NIM (Nuclear Instrumentation Module) standard, for
example for external triggers and veto, and to have the signals accessible.

The main component of the FTM board is a FPGA (Xilinx Spartan
XC3SD3400A-4FGG676C), fulfilling the main functions within the board. The
purpose of this document is to provide specifications needed for the
development of the firmware of this FPGA and the software (called 'FTMcontrol'
in the following) controlling the FTM board. For further information about the
FTM board hardware please refer to \cite{FTM-Schematics}.

\chapter{Trigger-ID}
\label{cha:Trigger-ID}

For each processed trigger the FTM board generates a unique trigger-ID to be
broadcasted to all FAD boards and added to the event data. This trigger-ID
consists of a 32 bit trigger number, a two byte trigger type indicator and a
checksum. The transmission protocol for the trigger-ID broadcast is shown in
table \ref{tab:Trigger-ID broadcast}.

\begin{table}[htbp]
\centering
\begin{tabular}{|l|l|}\hline
byte no & content\\\hline\hline
0 & Trigger-No first byte (least significant byte) \\\hline
1 & Trigger-No second byte\\\hline
2 & Trigger-No third byte\\\hline
3 & Trigger-No forth byte (most significant byte)\\\hline
4 & Trigger-Type 1\\\hline
5 & Trigger-Type 2\\\hline
6 & CRC-8-CCITT (checksum)\\\hline
\end{tabular}
\caption{The transmission protocol to broadcast the trigger-ID to the FAD boards}
\label{tab:Trigger-ID broadcast}
\end{table}

A Cyclic Redundancy Check (CRC) over byte 0 - 5 is used to evaluate the
integrity of the trigger-ID. An 8-CCITT CRC has been chosen which is based on
the polynomial $x^8 + x^2 + x + 1$ (00000111, omitting the most significant
bit). The resulting 1-byte checksum comprises the last byte of the trigger-ID.
The transmission of the trigger-ID to the FAD boards is done by means of
dedicated RS-485 buses (one per crate).

In the first byte of the trigger type indicator (see table
\ref{tab:Trigger-Type 1}) n0 - n5 indicate the number of trigger primitives
required for a trigger, thus the 'n' of the 'n-out-of-40' majority
coincidence. The two flags 'external trigger 1' and 'external trigger 2',
when set, indicate a trigger from the corresponding NIM inputs. See also
section \ref{sec:Static-data-block} and table \ref{tab:FTM-majority} for
further information.

\begin{table}[htbp]
\centering
%\begin{small}
\begin{tabular}{|l|l|l|l|l|l|l|l|}\hline
  Bit7 & Bit6 & Bit5 & Bit4 & Bit3 & Bit2 & Bit1 & Bit0\\\hline\hline 
  n5 & n4 & n3 & n2 & n1 & n0 & external trigger 2 & external trigger 1\\\hline
\end{tabular}
%\end{small}
\caption{Trigger-Type 1}
\label{tab:Trigger-Type 1}
\end{table}

\begin{table}[htbp]
\centering
\begin{small}
\begin{tabular}{|l|l|l|l|l|l|l|l|}\hline
Bit7 & Bit6 & Bit5 & Bit4 & Bit3 & Bit2 & Bit1 & Bit0\\\hline\hline 
TIM source & LP\_set\_3 & LP\_set\_2 & LP\_set\_1 & LP\_set\_0 & pedestal & LP\_2 & LP\_1\\\hline
\end{tabular}
\end{small}
\caption{Trigger-Type 2}
\label{tab:Trigger-Type 2}
\end{table}

The 'TIM source' bit in 'Trigger-Type 2' (see table \ref{tab:Trigger-Type 2})
indicates the source of the timemarker signal: a '0' indicates the timemarker
being produced in the FPGA while a '1' indicates the timemarker coming from
the clock conditioner. The flags 'LP\_1' and 'LP\_2' are set when the
corresponding lightpulser has flashed while the 'pedestal' flag is set in case
of a pedestal (random) trigger. An event having none of these flags set
indicates a physics event. The bits 'LP\_set\_0' to 'LP\_set\_3' are used to
code information about the light pulser settings. They only have a meaning in
case of calibration events.

\chapter{FTM Commands}
\label{cha:FTM-Commands}

The communication between the FTM board and the FTMcontrol software, including
the corresponding commands, protocols and data, is based on 16-bit words and
big-endian. This is to facilitate the data-transmission over the Wiznet W5300
ethernet interface \cite{W5300}.

The basic structure of all commands is the same and given in table
\ref{tab:FTM-command-structure}. After a start delimiter, the second word
identifies the command. Next there is a parameter further refining the
command, e.g. what to read. The fourth and fifth words are spares and should
contain zeros. Starting from the sixth word, an optional data block of
variable size is following. This data block differs in length and content
depending on command and parameter. In case of 'read' instructions, the
corresponding data block is sent back.

%The FTM board must answer every command by sending back the appropriate data
%block or by simply sending back the instruction where there is no datablock to
%be sent back.  All 'read' commands to the FTM board do not contain any data
%blocks, but the FTM boards response does.  In case of 'read' and 'write'
%instructions, the datablock is to be sent back. When 'start run' or 'stop run'
%commands are used, the FTM board 'mirrors' them, i.e. sends them back for
%confirmation.

\begin{table}[p]
\centering
\begin{tabular}{|l|l|}\hline
  word no & content\\\hline\hline
  0 & start delimiter (e.g. '@') \\\hline
  1 & command ID \\\hline
  2 & command parameter \\\hline
  3 & spare: containing 0x0000\\\hline
  4 & spare: containing 0x0000 \\\hline
  5 & data block (optional and of variable size)\\\hline
  ... & ...\\\hline
  X & data block\\\hline
\end{tabular}
\caption{FTM command structure}
\label{tab:FTM-command-structure}
\end{table}

So far seven different commands are foreseen: 'read', 'write', 'start run',
'stop run', 'ping FTUs', 'crate reset' and 'autosend on/off' (see table
\ref{tab:FTM-command-ID}). The command parameters of the 'read' and write
commands are shown in table~\ref{tab:FTM-read-command-param} and
table~\ref{tab:FTM-write-command-param}, respectively. With the 'autosend
on/off' command it is possible to switch off the automatic sending of trigger
rates and error messages (see table~\ref{tab:FTM-as-command-param}).

\begin{table}[p]
\centering
\begin{tabular}{|r|r|}\hline
  command-ID: bits & \\\cline{1-1}
  15 ... 8 \vline 7 \vline 6 \vline 5 \vline 4 \vline 3 \vline 2 \vline 1 \vline 0 & command\\\hline\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 & read \\\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 & write \\\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 \vline 0 & start run / take X events\\\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 \vline 0 \vline 0 & stop run \\\hline
  0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 \vline 0 \vline 0 \vline 0 & ping all FTUs \\\hline
  0 \vline 0 \vline 0 \vline 1 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 & crate reset \\\hline
  0 \vline 0 \vline 1 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 & autosend on/off \\\hline
\end{tabular}
\caption{FTM command ID listing}
\label{tab:FTM-command-ID}
\end{table}

\begin{table}[p]
\centering
\begin{tabular}{|r|r|r|}\hline
  command parameter: bits & & \\\cline{1-1}
  15 ... 8 \vline 7 \vline 6 \vline 5 \vline 4 \vline 3 \vline 2 \vline 1 \vline 0 & command & data block\\\hline\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 & read complete static data block & no\\\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 & read complete dynamic data block & no\\\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 \vline 0 &
  read single address of static data block & address\\\hline
  %0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 \vline 0 & read trigger list & no\\\hline
\end{tabular}
\caption{Command parameters for the 'read' command; only for the static data
  block single addresses can be read.}
\label{tab:FTM-read-command-param}
\end{table}

\begin{table}[p]
\centering
\begin{tabular}{|r|r|r|}\hline
  command parameter: bits & & \\\cline{1-1}
  15 ... 8 \vline 7 \vline 6 \vline 5 \vline 4 \vline 3 \vline 2 \vline 1 \vline 0 & command & data block\\\hline\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 & write complete static data block & all configuration data\\\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 \vline 0 &
  write single address of static data block & address + data\\\hline
\end{tabular}
\caption{Command parameters for the 'write' command; only the static data
  block can be written, therefore parameter value 0x2 is not used.}
\label{tab:FTM-write-command-param}
\end{table}

\begin{table}[p]
\centering
\begin{tabular}{|r|r|r|}\hline
  command parameter: bits & & \\\cline{1-1}
  15 ... 8 \vline 7 \vline 6 \vline 5 \vline 4 \vline 3 \vline 2 \vline 1 \vline 0 & command & data block\\\hline\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 & reports disabled & no\\\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 & reports enabled & no\\\hline
\end{tabular}
\caption{Command parameters for the 'autosend on/off' command}
\label{tab:FTM-as-command-param}
\end{table}

%\begin{table}[htbp]
%\centering
%\begin{tabular}{|r|r|r|}\hline
%  command parameter: bits & & \\\cline{1-1}
%  15 ... 8  \vline 7  \vline 6  \vline 5 \vline 4 \vline 3 \vline 2 \vline 1 \vline 0 & command & data block\\\hline\hline
%  0 \vline 0 \vline 0 \vline 0 \vline 0  \vline0 \vline 0  \vline0  \vline1 & write static data & static data block\\\hline
%\end{tabular}
%\caption{Command parameters for the 'write' command}
%\label{tab:FTM-write-command-param}
%\end{table}

In table \ref{tab:FTM-start-command-param} the parameters to start a run are
listed. The type of the run is fully described in the FTM configuration
(static data block, see section~\ref{sec:Static-data-block}), which always has
to be sent by the FTMcontrol before starting a run. Therefore the only
option is to start an "endless" run or to take X events instead. In the latter
case X is defined by a two words (32 bit) long unsigned integer, making up the
command data block. The 'start run' command enables the transmission of
trigger signals (physics, calibration or pedestal) to the FAD boards and
resets the trigger and time counters. There is no parameter for stopping a
run. If a number of events has been specified ('take X events'), the run will
terminate if either the 'stop run' command is received or the requested number
of events is reached. In any case the trigger and time counters are reset,
too.

\begin{table}[p]
\centering
\begin{tabular}{|r|r|r|}\hline
  command parameter: bits & & \\\cline{1-1}
  15 ... 8  \vline7  \vline 6 \vline 5 \vline 4 \vline 3 \vline 2 \vline 1 \vline 0 & command & data block\\\hline\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 & start run & no \\\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 & take X events & number of events X \\\hline
  %0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 \vline 0 & start taking pedestals & no \\\hline
  %0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 \vline 1 & take X pedestals events & number of events X \\\hline
  %0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 \vline 0 \vline 0 & start calibration run & no \\\hline
  %0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 \vline 0 \vline 1 & take X calibration events & number of events X \\\hline
\end{tabular}
\caption{Command parameters for the 'start run' command: "start run" means an
  "endless" run, i.e. no pre-defined number of events; if a number of events X
  is specified, this is done with a 32-bit unsigned long integer (big endian).}
\label{tab:FTM-start-command-param}
\end{table}

%\begin{table}[htbp]
%\centering
%\begin{tabular}{|r|r|r|}\hline
%  command parameter: bits & & \\\cline{1-1}
%  15 ... 8  \vline 7 \vline 6 \vline 5 \vline 4  \vline 3 \vline 2 \vline 1 \vline 0 & command & data block\\\hline\hline
%  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 & stop run & no\\\hline
%\end{tabular}
%\caption{Command parameter for the 'stop run' command}
%\label{tab:FTM-stop-command-param}
%\end{table}

In case of a 'ping FTUs' command the FTM will address the FTUs one by one and
readout their DNA. The results are collected in the FTU list (see section
\ref{sec:FTU-List}), which is sent back to the FTMcontrol. There are no
parameters for this command. With the 'crate reset' command the boards of a
particular crate can be rebooted, where the command parameter defines the
crate number (see table \ref{tab:FTM-reset-command-param}). Only one crate
reset at a time is possible, i.e. the FTM firmware does not allow to reset
multiple crates in one command.

\begin{table}[p]
\centering
\begin{tabular}{|r|r|r|}\hline
  command parameter: bits & & \\\cline{1-1}
  15 ... 8 \vline 7 \vline 6 \vline 5 \vline 4 \vline 3 \vline 2 \vline 1 \vline 0 & command & data block\\\hline\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 & reset crate 0 & no\\\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 & reset crate 1 & no\\\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 \vline 0 & reset crate 2 & no\\\hline
  0 \vline 0 \vline 0 \vline 0 \vline 0 \vline 1 \vline 0 \vline 0 \vline 0 & reset crate 3 & no\\\hline
\end{tabular}
\caption{Command parameters for the 'crate reset' command: the command parameter may only contain a single "1"
         corresponding to only one crate reset at a time.}
\label{tab:FTM-reset-command-param}
\end{table}

\chapter{FTM data blocks}
\label{cha:FTM-data-block}

The trigger master features two main data blocks, named 'static data block'
and 'dynamic data block' in the following. They are implemented in the
firmware as block-RAM. In addition, there is the so-called 'FTU list', which
is filled only on request ('ping FTUs' command). If any of these blocks is
sent to the FTMcontrol (either automatically or on demand), a header with a
size of 14 words is added, and the whole data package is put between a start
and an end delimiter (see table~\ref{tab:FTM-package}). The header is
identical for all data blocks and contains solely read-only information: the
type and length of the package, the FTM status, the FTM board ID (57-bit
Xilinx device DNA \cite{ds557, ds610, wp267, wp266}), a firmware ID and the
readings of the trigger counter and time stamp counter (see
table~\ref{tab:FTM-header}).

\begin{table}[h]
\centering
\begin{tabular}{|c|c|c|c|}\hline
  start delimiter & header & data block & end delimiter \\\hline
  0xFB01 & 14 words & optional size & 0x04FE\\\hline
\end{tabular}
\caption{Structure of a data package as sent by the FTM to the FTMcontrol
  software. The start and end delimiters are the same as used for the FAD boards.}
\label{tab:FTM-package}
\end{table}

\begin{table}[h]
\centering
\begin{tabular}{|l|l|c|}\hline
  word no & content & description\\\hline\hline
  0x000 & type of data package & 1: SD, 2: DD, 3: FTU-list, 4: error, 5: single SD-word\\\hline
  0x001 & length of data package & after header, including end delimiter\\\hline
  0x002 & status of FTM & 1: IDLE, 2: CONFIG, 3: RUNNING, 4: CALIB\\\hline
  0x003 & board ID bits 63...48 & FPGA device DNA\\\hline
  0x004 & board ID bits 47...32 & FPGA device DNA\\\hline
  0x005 & board ID bits 31...16 & FPGA device DNA\\\hline
  0x006 & board ID bits 15... 0 & FPGA device DNA\\\hline
  0x007 & firmware ID & defined as a VHDL constant\\\hline
  0x008 & trigger counter bits 31...16 & at read-out time\\\hline
  0x009 & trigger counter bits 15... 0 & at read-out time\\\hline
  0x00A & time stamp bits 63...48 & filled up with zeros\\\hline
  0x00B & time stamp bits 47...32 & at read-out time\\\hline
  0x00C & time stamp bits 31...16 & at read-out time\\\hline
  0x00D & time stamp bits 15... 0 & at read-out time\\\hline
\end{tabular}
\caption{Header structure for sending a data block or error message}
\label{tab:FTM-header}
\end{table}

\section{Static data block}
\label{sec:Static-data-block}

The static data block contains all the settings needed to configure and
operate the FTM. It has to be written by the FTMcontrol each time before a run
is started or, in general, some component has to be reprogrammed. Single
register access is possible, but not foreseen for the standard data taking. In
addition, whenever the FTM board receives a new static data block, it performs
a complete reconfiguration including a reprogramming of the
FTUs. Table~\ref{tab:FTM-trigger-master-static-data-block} summarizes the
static data block. More details about the individual registers can be found in
the subsequent tables.

%These settings are readable and writable by the main control using the
%corresponding commands 'read static data block' or 'write static data block',
%respectively.  There is one exception from writability: In case the static
%data block is read back, the first eleven words (address 0..A) are identical
%with the dynamic data block and the trigger list shown in
%\ref{tab:FTM-trigger-master-dynamic-data-block} and
%\ref{tab:FTM-trigger-list}.  These first eleven words can only be read and not
%written.  The board ID is supposed to be the Xilinx device DNA \cite{ds557,
%  ds610, wp267, wp266}, the 57 bit device ID of the FPGA.  When using the
%'write static data block' command, the static data block must start with the
%'general settings register' at address 0x00B. So there is an offset in the
%addresses of 0x00B between the 'read-out-version' and the 'write-version' of
%the static data block.

\begin{longtable}[h]{|l|l|c|}\hline
\centering
word no & content & description\\\hline\hline
0x000 & general settings & see table~\ref{tab:FTM-general-settings-register} and text\\\hline
0x001 & on-board status LEDs & see table~\ref{tab:FTM-LED-register}\\\hline
0x002 & light pulser and pedestal trigger period & see table~\ref{tab:FTM-frequency-register} and text\\\hline
0x003 & sequence of LP1, LP2 and PED triggers & see table~\ref{tab:FTM-ratio-register} and text\\\hline

0x004 & light pulser 1 amplitude & see table~\ref{tab:LP1-amplitude-register} and text\\\hline
0x005 & light pulser 2 amplitude & see table~\ref{tab:LP2-amplitude-register} and text\\\hline
0x006 & light pulser 1 delay & 8ns + delay value*4ns\\\hline
0x007 & light pulser 2 delay & 8ns + delay value*4ns\\\hline

0x008 & majority coincidence n (for physics) & see table~\ref{tab:FTM-majority} and text\\\hline
0x009 & majority coincidence n (for calibration) & see table~\ref{tab:FTM-majority} and text\\\hline
0x00A & trigger delay & 8ns + delay value*4ns, 10 bits used\\\hline
0x00B & timemarker delay & 8ns + delay value*4ns, 10 bits used\\\hline
0x00C & dead time & 8ns + value*4ns, 16 bits used\\\hline
0x00D & clock conditioner R0 bits 31...16 & \\\hline
0x00E & clock conditioner R0 bits 15...0 & \\\hline
0x00F & clock conditioner R1 bits 31...16 & \\\hline
0x010 & clock conditioner R1 bits 15...0 & \\\hline
0x011 & clock conditioner R8 bits 31...16 & \\\hline
0x012 & clock conditioner R8 bits 15...0 & \\\hline
0x013 & clock conditioner R9 bits 31...16 & \\\hline
0x014 & clock conditioner R9 bits 15...0 & \\\hline
0x015 & clock conditioner R11 bits 31...16 & \\\hline
0x016 & clock conditioner R11 bits 15...0 & \\\hline
0x017 & clock conditioner R13 bits 31...16 & \\\hline
0x018 & clock conditioner R13 bits 15...0 & \\\hline
0x019 & clock conditioner R14 bits 31...16 & \\\hline
0x01A & clock conditioner R14 bits 15...0 & \\\hline
0x01B & clock conditioner R15 bits 31...16 & \\\hline
0x01C & clock conditioner R15 bits 15...0 & \\\hline
0x01D & maj. coinc. window (for physics) & 8ns + value*4ns, 4 bits used\\\hline
0x01E & maj. coinc. window (for calibration) & 8ns + value*4ns, 4 bits used \\\hline
0x01F & spare & \\\hline
0x020 & enables patch 0 board 0 crate 0 & see FTU documentation\\\hline
0x021 & enables patch 1 board 0 crate 0 & see FTU documentation\\\hline
0x022 & enables patch 2 board 0 crate 0 & see FTU documentation\\\hline
0x023 & enables patch 3 board 0 crate 0 & see FTU documentation\\\hline
0x024 & DAC$\_$A board 0 crate 0 & see FTU documentation \\\hline
0x025 & DAC$\_$B board 0 crate 0 & see FTU documentation \\\hline
0x026 & DAC$\_$C board 0 crate 0 & see FTU documentation \\\hline
0x027 & DAC$\_$D board 0 crate 0 & see FTU documentation \\\hline
0x028 & DAC$\_$H board 0 crate 0 & see FTU documentation \\\hline
0x029 & Prescaling board 0 crate 0 & (value+1)/2~[s], also autosend period \\\hline
0x02A & enables patch 0 board 1 crate 0 & see FTU documentation  \\\hline
0x02B & enables patch 1 board 1 crate 0 & see FTU documentation  \\\hline
0x02C & enables patch 2 board 1 crate 0 & see FTU documentation  \\\hline
0x02D & enables patch 3 board 1 crate 0 & see FTU documentation  \\\hline
0x02E & DAC$\_$A board 1 crate 0 & see FTU documentation \\\hline
0x02F & DAC$\_$B board 1 crate 0 & see FTU documentation \\\hline
0x030 & DAC$\_$C board 1 crate 0 & see FTU documentation \\\hline
0x031 & DAC$\_$D board 1 crate 0 & see FTU documentation \\\hline
0x032 & DAC$\_$H board 1 crate 0 & see FTU documentation \\\hline
0x033 & Prescaling board 1 crate 0 & see FTU documentation \\\hline
... & ... & \\\hline
0x1A6 & enables patch 0 board 9 crate 3 & see FTU documentation \\\hline
0x1A7 & enables patch 1 board 9 crate 3 & see FTU documentation \\\hline
0x1A8 & enables patch 2 board 9 crate 3 & see FTU documentation \\\hline
0x1A9 & enables patch 3 board 9 crate 3 & see FTU documentation \\\hline
0x1AA & DAC$\_$A board 9 crate 3 & see FTU documentation \\\hline
0x1AB & DAC$\_$B board 9 crate 3 & see FTU documentation \\\hline
0x1AC & DAC$\_$C board 9 crate 3 & see FTU documentation \\\hline
0x1AD & DAC$\_$D board 9 crate 3 & see FTU documentation \\\hline
0x1AE & DAC$\_$H board 9 crate 3 & see FTU documentation \\\hline
0x1AF & Prescaling board 9 crate 3 & see FTU documentation \\\hline
0x1B0 & active FTU list crate 0 & see FTU documentation \\\hline
0x1B1 & active FTU list crate 1 & see FTU documentation \\\hline
0x1B2 & active FTU list crate 2 & see FTU documentation \\\hline
0x1B3 & active FTU list crate 3 & see FTU documentation \\\hline 
\caption{Overview of the FTM static data block}
\label{tab:FTM-trigger-master-static-data-block}
\end{longtable}

The FTM general settings register is detailed in table
\ref{tab:FTM-general-settings-register}. The 'TIM\_CLK' bit defines whether
the time marker is generated by the FPGA ('TIM\_CLK' = 0, default for physics
data taking), or whether it is generated by the clock conditioner ('TIM\_CLK'
= 1, e.g. for DRS timing calibration). The 'ext\_veto', 'ext\_trig\_1' and
'ext\_trig\_2' bits enable (1) or disable (0) the NIM inputs for the external
veto and trigger signals, respectively. In order to select which trigger
sources are active during a run, the bits 'LP1', 'LP2', 'ped' and 'trigger'
are foreseen (0 disabled, 1 enabled). During a physics run, for example,
'LP1', 'ped' and 'trigger' should all be set to generate interleaved
calibration and pedestal events as well as activate the 'n-out-of-40' trigger
input. For a didicated pedestal run only 'ped' should be set, since in this
case the FTM sends directly a trigger to the FADs. For calibration runs it
depends on whether the external (LP1) or internal (LP2) light pulser is used:
For the first case 'LP1' and 'trigger' have to be set, since here the full
trigger chain is involved and the camera triggers based on G-APD signals. For
the second case only 'LP2' is needed, because the shutter is closed and the
FTM sends directly the trigger signal to the FADs (like for pedestal
events). Bits 8 to 15 of the general settings register are not used up to now.

\begin{table}[h]
\centering
\begin{small}
\begin{tabular}{|l|l|l|l|l|l|l|l|l|l|}\hline
Bit & 15...8 & 7 & 6 & 5 & 4 & 3 & 2 & 1 & 0 \\\hline
Content & x & trigger & ped & LP2 & LP1 & ext\_trig\_2 & ext\_trig\_1& ext\_veto & TIM\_CLK \\\hline
\end{tabular}
\end{small}
\caption{FTM general settings register}
\label{tab:FTM-general-settings-register}
\end{table}

%\begin{table}[!h]
%\centering
%\begin{tabular}{|l|l|}\hline
%TIM\_CClk & description \\\hline\hline
%0 & Time marker generated in the FPGA \\\hline
%1 & Time marker generated by the clock conditioner \\\hline
%\end{tabular}
%\caption{FTM Time marker indication}
%\label{tab:FTM-Time-marker-indication}
%\end{table}

%\begin{table}[!h]
%\centering
%\begin{tabular}{|l|l|}\hline
%ena$\_$ext$\_$Veto  & description \\\hline\hline
%0 & disable external trigger veto\\\hline
%1 & enable external trigger veto \\\hline
%\end{tabular}
%\caption{FTM external trigger}
%\label{tab:FTM-external-trigger}
%\end{table}

%\begin{table}[!h]
%\centering
%\begin{tabular}{|l||l|}\hline
%ena\_LP1  & description \\\hline\hline
%0 & disable light pulser 1 \\\hline
%1 & enable light pulser 1\\\hline
%\end{tabular}
%\caption{FTM light pulser 1}
%\label{tab:FTM-light-pulser-1}
%\end{table}

%\begin{table}[!h]
%\centering
%\begin{tabular}{|l||l|}\hline
%ena\_LP2  & description \\\hline\hline
%0 & disable light pulser 2 \\\hline
%1 & enable light pulser 2 \\\hline
%\end{tabular}
%\caption{FTM light pulser 2}
%\label{tab:FTM-light-pulser-2}
%\end{table}

%\begin{table}[!h]
%\centering
%\begin{tabular}{|l||l|}\hline
%ena\_Ped  & description \\\hline\hline
%0 & disable interleaved pedestal trigger \\\hline
%1 & enable interleaved pedestal trigger \\\hline
%\end{tabular}
%\caption{FTM interleaved pedestals}
%\label{tab:FTM-interleaved-pedestals}
%\end{table}

%\begin{table}[!h]
%\centering
%\begin{small}
%\begin{tabular}{|l||l|}\hline
%ena\_LLC  & description \\\hline\hline
%0 & disable low level calibration pulses \\\hline
%1 & enable low level calibration pulses \\\hline
%\end{tabular}
%\end{small}
%\caption{FTM low level calibration pulses}
%\label{tab:FTM-low-level-calibration-pulses}
%\end{table}

The 'on-board status LEDs' register shown in table \ref{tab:FTM-LED-register}
allows to switch a total of eight LEDs on the FTM board for debugging purposes
by setting the corresponding bit high.

\begin{table}[h]
\centering
\begin{small}
\begin{tabular}{|l|l|l|l|l|l|l|l|l|l|}\hline
Bit      & 15...8 & 7 & 6 & 5 & 4 & 3 & 2 & 1 & 0 \\\hline
Content &  x & red$\_$3 & red$\_$2 & gn$\_$1 & ye$\_$1 & red$\_$1 & gn$\_$0 & ye$\_$0 & red$\_$0 \\\hline
\end{tabular}
\end{small}
\caption{'on-board status LEDs' register}
\label{tab:FTM-LED-register}
\end{table}

The period (time distance, see table \ref{tab:FTM-frequency-register}), with
which light pulser and pedestal triggers are sent, is stored in the register
at address 0x002. It is given in [ms] and adjustable between 1\,ms and
1023\,ms (10 bits used). The next register defines the sequence of LP1, LP2
and pedestal events (see table \ref{tab:FTM-ratio-register}).
 
\begin{table}[h]
\centering
\begin{small}
\begin{tabular}{|l|l|l|l|l|l|l|l|}\hline
Bit      & 15 - 10 & 9 & 8 & ... & 2 & 1 & 0 \\\hline
Content &  x  & PERIOD\_9 & PERIOD\_8 & ... & PERIOD\_2 & PERIOD\_1 & PERIOD\_0 \\\hline
\end{tabular}
\end{small}
\caption{Register for the period [ms] of calibration and pedestal events}
\label{tab:FTM-frequency-register}
\end{table}

\begin{table}[h]
\centering
\begin{small}
\begin{tabular}{|l|l|l|l|l|l|l|l|l|l|l|}\hline
Bit      & 15 & 14 & ... & 10 & 9 & ... & 5 & 4 & ... & 0 \\\hline
Content & x & ped\_S4 & ... & ped\_S0 & LP2\_S4 & ... & LP2\_S0 & LP1\_S4 & ... & LP1\_S0 \\\hline
\end{tabular}
\end{small}
\caption{Register defining the sequence of LP1, LP2 and pedestal events; 5
  bits used per value. By setting e.g. LP1/LP2/PED = 3/2/1, the systems
  generates 3 LP1 triggers, followed by 2 LP2 triggers, followed by 1 PED
  trigger (if they are also activated in the 'general settings' register).
  The distance between the triggers is defined with another register
  (table~\ref{tab:FTM-frequency-register}).}
\label{tab:FTM-ratio-register}
\end{table}

%\begin{table}[!h]
%\centering
%\begin{tiny}
%\begin{tabular}{|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|l|}\hline
%Bit      & 15 - 10 & 9 & 8 & 7 & 6 & 5 & 4 & 3 & 2 & 1 & 0 \\\hline
%Function &  x  & LPR2\_9 & LPR2\_8 & LPR2\_7 & LPR2\_6 & LPR2\_5 & LPR2\_4 & LPR2\_3 & LPR2\_2 & LPR2\_1 & LPR2\_0 \\\hline
%\end{tabular}
%\end{tiny}
%\caption{Light pulser 2 frequency register at address 0x00E: This register contains the pulse rate of the light
%               pulser 2 in Hz.}
%\label{tab:Light-pulser-2-frequancy-register}
%\end{table}











In order to define the amplitude and characteristics of the light pulses that
are generated by the LP1 and the LP2 system, the registers 'LP1 amplitude' and
'LP2 amplitude' are used, respectively. These registers are presented in
table~\ref{tab:LP1-amplitude-register} and table~\ref{tab:LP2-amplitude-register}.
The two most significant bit allow to switch on additional LEDs, while the six
least significant bits are used for the FM (frequency modulation) on the 
light pulser board. These six bits (FM1\_5 ... FM1\_0 and FM2\_5 ... FM2\_0
respectively) are frequency dividing factors and the resulting frequency for the 
feedback is $ f_{FM} = \frac{5MHz}{25 +  \mid FM1\_5 ... FM1\_0 \mid} $.




This FM signal is used for stabilizing the amplitude
of the light pulses, see the schematics \cite{FLD-Schematics}.

The light pulser systems are controlled from the FTM by means of four LVDS control lines:
The first line goes directly to the LED driver circuit and triggers a lightpulse.
The FM signal is on the second line.
The third and forth line allow to switch on additional LEDs.








\begin{table}[!h]
\centering
\begin{small}
\begin{tabular}{|l|l|l|l|l|}\hline
Bit      & 15 & 14 & 13 ... 6 & 5 ... 0 \\\hline
Content &  add\_LEDs1\_1& add\_LEDs1\_0 & x & FM1\_5 ... FM1\_0 \\\hline
\end{tabular}
\end{small}
\caption{Light pulser 1 amplitude register}
\label{tab:LP1-amplitude-register}
\end{table}




\begin{table}[!h]
\centering
\begin{small}
\begin{tabular}{|l|l|l|l|l|}\hline
Bit      & 15 & 14 & 13 ... 6 & 5 ... 0 \\\hline
Content &  add\_LEDs2\_1& add\_LEDs2\_0 & x & FM2\_5 ... FM2\_0 \\\hline
\end{tabular}
\end{small}
\caption{Light pulser 2 amplitude register}
\label{tab:LP2-amplitude-register}
\end{table}

















The different settings of the 'n-out-of-40' logic (physics or calibration
events) are stored in two separate registers, which both have a structure
according to table~\ref{tab:FTM-majority}.

\begin{table}[!h]
\centering
\begin{small}
\begin{tabular}{|l|l|l|l|l|l|l|l|}\hline
Bit      & 15...6 & 5 & 4 & 3 & 2 &1 & 0 \\\hline
Content & x & n5 & n4 & n3 & n2 & n1 & n0 \\\hline
\end{tabular}
\end{small}
\caption{Structure of the two majority coincidence (n-out-of-40) registers; the binary value
  in these registers is the minimum number n of FTU trigger primitives required to trigger an event (physics or calibration)}
\label{tab:FTM-majority}
\end{table}

In addition, there are several registers in the static data block to define
delays (e.g. for the trigger). Also a general dead time to be applied after
each trigger can be set (to compensate for the delay of the busy line). The
clock conditioner settings are specified at address 0x00D to 0x01C (LMK03000
from National Semiconductor, for more details see \cite{LMK03000}).

Starting at address 0x020, the FTU settings are stored. The FTM always holds
the complete FTU parameters in the static data block. For the meaning of these
registers, please refer to the FTU firmware specifications document
\cite{FTUspecs}. The register at address 0x029 is special in the sense that,
in addition to its normal meaning, it also defines the time period with which
the FTU rates are sent automatically to the FTMcontrol software. In case not
all FTUs are connected during e.g. the testing phase, or a FTU is broken, the
'active FTU list' registers can be used to disable certain boards. Bits 9...0
of one of the active FTU lists (address 0x1B0 to 0x1B3, corresponding to crate
0 to 3) contain the "active" flag for every FTU board. Setting a bit activates
the corresponding FTU board while a "0" deactivates it.

\section{Dynamic data block}
\label{sec:Dynamic-data-block}
The dynamic data block shown in table \ref{tab:FTM-dynamic-data-block}
contains permanently updated data stored inside the FTM FPGA. It contains the
actual on-time counter reading, the board temperatures and the trigger rates
measured by the FTUs. This data block is updated and sent periodically by the
FTM. Thus the FTMcontrol software receives periodically a corresponding data
package via ethernet. The counting interval of the FTU board 0 on crate 0
('prescaling' register) defines the period. The on-board 12-bit temperature
sensors are MAX6662 chips from Maxim Products. For more information about
these components and their data see \cite{MAX6662}. When sending the dynamic
data block, the header defined in table~\ref{tab:FTM-header} is added at the
beginning.

\newpage

% \begin{table}[h]
%  \centering
\begin{longtable}[h]{|l|l|}\hline
word no & content\\\hline\hline
0x000 & on-time counter at read-out time bits 63...48, filled up with zeros \\\hline
0x001 & on-time counter at read-out time bits 47...32 \\\hline
0x002 & on-time counter at read-out time bits 31...16 \\\hline
0x003 & on-time counter at read-out time bits 15...0 \\\hline
0x004 & temperature sensor 0: component U45 on the FTM schematics \cite{FTM-Schematics}\\\hline
0x005 & temperature sensor 1: U46 \\\hline
0x006 & temperature sensor 2: U48 \\\hline
0x007 & temperature sensor 3: U49 \\\hline
0x008 & rate counter bit 29...16 patch 0 board 0 crate 0 \\\hline
0x009 & rate counter bit 15...0 patch 0 board 0 crate 0 \\\hline
0x00A & rate counter bit 29...16 patch 1 board 0 crate 0 \\\hline
0x00B & rate counter bit 15...0 patch 1 board 0 crate 0 \\\hline
0x00C & rate counter bit 29...16 patch 2 board 0 crate 0 \\\hline
0x00D & rate counter bit 15...0 patch 2 board 0 crate 0 \\\hline
0x00E & rate counter bit 29...16 patch 3 board 0 crate 0 \\\hline
0x00F & rate counter bit 15...0 patch 3 board 0 crate 0 \\\hline
0x010 & rate counter bit 29...16 total board 0 crate 0 \\\hline
0x011 & rate counter bit 15...0 total board 0 crate 0\\\hline
0x012 & Overflow register board 0 crate 0 \\\hline
0x013 & CRC-error register board 0 crate 0 \\\hline
0x014 & rate counter bit 29...16 patch 0 board 1 crate 0 \\\hline
0x015 & rate counter bit 15...0 patch 0 board 1 crate 0 \\\hline
0x016 & rate counter bit 29...16 patch 1 board 1 crate 0 \\\hline
0x017 & rate counter bit 15...0 patch 1 board 1 crate 0 \\\hline
0x018 & rate counter bit 29...16 patch 2 board 1 crate 0 \\\hline
0x019 & rate counter bit 15...0 patch 2 board 1 crate 0 \\\hline
0x01A & rate counter bit 29...16 patch 3 board 1 crate 0 \\\hline
0x01B & rate counter bit 15...0 patch 3 board 1 crate 0 \\\hline
0x01C & rate counter bit 29...16 total board 1 crate 0 \\\hline
0x01D & rate counter bit 15...0 total board 1 crate 0  \\\hline
0x01E & Overflow register board 1 crate 0 \\\hline
0x01F & CRC-error register board 1 crate 0 \\\hline
... & ... \\\hline
0x1E7 & CRC-error register board 9 crate 3 \\\hline
% \end{longtable}
\caption{FTM dynamic data block}
\label{tab:FTM-dynamic-data-block}
\end{longtable}

%\section{Trigger-list}
%\label{sec:trigger-list}
%The FTM board records all triggers in a list, the so-called trigger-list.
%This trigger-list comprises a maximum of 50 triggers.  The first eleven words
%are the same as in the static- and dynamic data block.  During data-taking-,
%calibration- and trigger runs, the Trigger-list is automatically sent to the
%main control each time the 50 triggers are reached or the run is finished. In
%addition, the Trigger-list can also be read-out by the main control with the
%according command.  In case the run finishes or is terminated, as well as when
%read out manually, the trigger list might be shorter than 50 events.

%% \begin{table}[h]
%% \centering
%\begin{longtable}[h]{|l|l|}\hline
%address & content\\\hline\hline
%0x000 & board ID bit 63 - 48 \\\hline
%0x001 & board ID bit 47 - 32\\\hline
%0x002 & board ID bit 31 - 16\\\hline
%0x003 & board ID bit 15 - 0\\\hline
%0x004 & firmware ID \\\hline
%0x005 & Trigger counter at read-out time bits 31 .. 16 \\\hline
%0x006 & Trigger counter at read-out time bits 15 .. 0\\\hline
%0x007 & Time stamp counter at read-out time bits 47 .. 32 \\\hline
%0x008 & Time stamp counter at read-out time bits 31 .. 16 \\\hline
%0x009 & Time stamp counter at read-out time bits 15 .. 0 \\\hline
%0x00A & spare \\\hline

%0x00B & on-time counter at read-out time bits 47 .. 32 \\\hline
%0x00C & on-time counter at read-out time bits 31 .. 16 \\\hline
%0x00D & on-time counter at read-out time bits 15 .. 0 \\\hline

%0x00E & 1st event Trigger-ID \\\hline
%0x00F & 1st event Trigger-ID \\\hline
%0x010 & 1st event Trigger-ID \\\hline
%0x011 & 1st event Trigger primitives crate 0 \\\hline
%0x012 & 1st event Trigger primitives crate 1 \\\hline
%0x013 & 1st event Trigger primitives crate 2 \\\hline
%0x014 & 1st event Trigger primitives crate 3 \\\hline
%0x015 & 1st event Time stamp counter at trigger time bits 47 .. 32 \\\hline
%0x016 & 1st event Time stamp counter at trigger time bits 31 .. 16 \\\hline
%0x017 & 1st event Time stamp counter at trigger time bits 15 .. 0 \\\hline

%0x018 & 2nd event Trigger-ID \\\hline
%0x019 & 2nd event Trigger-ID \\\hline
%0x01A & 2nd event Trigger-ID \\\hline
%0x01B & 2nd event Trigger primitives crate 0 \\\hline
%0x01C & 2nd event Trigger primitives crate 1 \\\hline
%0x01D & 2nd event Trigger primitives crate 2 \\\hline
%0x01E & 2nd event Trigger primitives crate 3 \\\hline
%0x01F & 2nd event Time stamp counter at trigger time bits 47 .. 32 \\\hline
%0x020 & 2nd event Time stamp counter at trigger time bits 31 .. 16 \\\hline
%0x021 & 2nd event Time stamp counter at trigger bits 15 .. 0 \\\hline
%... & ...\\\hline
%0x1F8 & 50th event Trigger-ID \\\hline
%0x1F9 & 50th event Trigger-ID \\\hline
%0x1FA & 50th event Trigger-ID \\\hline
%0x1FB & 50th event Trigger primitives crate 0 \\\hline
%0x1FC & 50th event Trigger primitives crate 1 \\\hline
%0x1FD & 50th event Trigger primitives crate 2 \\\hline
%0x1FE & 50th event Trigger primitives crate 3 \\\hline
%0x1FF & 50th event Time stamp counter at trigger time bits 47 .. 32 \\\hline
%0x200 & 50th event Time stamp counter at trigger time bits 31 .. 16 \\\hline
%0x201 & 50th event Time stamp counter at trigger bits 15 .. 0 \\\hline

%% \end{longtable}
%\caption{FTM trigger list}
%\label{tab:FTM-trigger-list}
%\end{longtable}

\section{FTU list}
\label{sec:FTU-List}
When the FTM board receives the 'ping all FTUs' instruction, it sends a ping
command to all FTU boards and gathers the FTU boards responses to a list. This
list is called 'FTU list' and shown in table \ref{tab:FTU-list}. When the FTU
list is complete, it is sent back via ethernet with the header defined in
table~\ref{tab:FTM-header}.

\begin{longtable}[h]{|l|l|}\hline
address & content\\\hline\hline
0x000 & total number of responding FTU boards\\\hline
0x001 & number of responding FTU boards belonging to crate 0 \\\hline
0x002 & number of responding FTU boards belonging to crate 1 \\\hline
0x003 & number of responding FTU boards belonging to crate 2 \\\hline
0x004 & number of responding FTU boards belonging to crate 3 \\\hline
0x005 & active FTU list crate 0 \\\hline
0x006 & active FTU list crate 1 \\\hline
0x007 & active FTU list crate 2 \\\hline
0x008 & active FTU list crate 3 \\\hline 
0x009 & address of first FTU board and number of sent pings until response\\\hline
0x00A & DNA of first FTU board bit 63 ... 48\\\hline
0x00B & DNA of first FTU board bit 47 ... 32\\\hline
0x00C & DNA of first FTU board bit 31 ... 16\\\hline
0x00D & DNA of first FTU board bit 15 ... 0\\\hline
0x00E & CRC error counter reading of first FTU board\\\hline
0x00F & address of second FTU board and number of sent pings until response\\\hline
0x010 & DNA of second FTU board bit 63 ... 48\\\hline
0x011 & DNA of second FTU board bit 47 ... 32\\\hline
0x012 & DNA of second FTU board bit 31 ... 16\\\hline
0x013 & DNA of second FTU board bit 15 ... 0\\\hline
0x014 & CRC error counter reading of second FTU board\\\hline
... & ...\\\hline
0x0F8 & CRC error counter reading of last FTU board\\\hline
\caption{FTU list}
\label{tab:FTU-list}
\end{longtable}

In case there is no response to a 'ping' for a certain FTU address, there are
up to two repetitions. If there is still no answer, only zeros are written
into the FTU list for this particular board. A responding FTU board gets a
regular entry, including the number of 'ping' sent until response. The number
of pings is coded together with the FTU board address as shown in table
\ref{tab:FTU-crate-number-and-address}. The two bits 'pings\_0' and 'pings\_1'
contain the number of 'pings' until response of an FTU board (coded in
binary). The 'DNA' of the FTU board is the device DNA \cite{ds557, ds610,
  wp267, wp266} of the FPGA on the responding FTU board. This is a unique 57
bit serial number unambiguously identifying every Xilinx FPGA. In the most
significant word (bit 63 ... 48) bits 63 down to 57 are filled with zeros.

\begin{table}[h]
\centering
\begin{tabular}{|l|l|l|l|l|l|l|l|l|l|l|l|l|}\hline
Bit      & 15 ... 10 & 9 & 8 & 7 & 6 & 5 & ... & 0 \\\hline
Content & x ... x & pings\_1 & pings\_0 & x & x & A5 & ... & A0 \\\hline
\end{tabular}
\caption{Address of FTU board and number of pings until response. In case
  there is no response at all, this number is set to 0.}
\label{tab:FTU-crate-number-and-address}
\end{table}

\chapter{FTU communication error handling}
\label{cha:Error-handling}

When the FTM board is communicating with a FTU board via RS-485, the FTU board
has to respond within 2\,ms (after the last byte was transmitted). If this
timeout expires, or the response sent back by the FTU board is incorrect, the
FTM resends the datapacket after the timeout. If this second attempt is still
unsuccessful, a third and last attempt will be made by the FTM board. An error
message will be sent to the FTMcontrol whenever a FTU board does not send a
correct answer after the first call by the FTM board. This message (see
table~\ref{tab:error-message}) contains, after the standard header (see
table~\ref{tab:FTM-header}), the number of calls until response (0 if no
response at all), and the corresponding data packet which was sent to the FTU
board. In order to avoid massive error messages for e.g. test setups with
single FTUs, the 'active FTU list' can be employed to disable FTUs from the
bus. In that case the FTM will not try to contact the corresponding boards.

\begin{table}[h]
  \centering
  \begin{tabular}{|l|l|}\hline
    word no & content\\\hline\hline
    0x000 & number of calls until response (0 if no response at all)\\\hline
    0x001 ... 0x01C & slow control data packet sent to FTU (28 words/bytes)\\\hline
  \end{tabular}
  \caption{FTU communication error message (after standard header); for a
    description of the FTU data package, see \cite{FTUspecs}.}
  \label{tab:error-message}
\end{table}

%---------------------------------------------------------------------------------

\bibliographystyle{unsrt}
%\bibliography{FTM-Com}

\begin{thebibliography}{1}

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\newblock datasheet.

\bibitem{FTM-Schematics}
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\bibitem{ds557}
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\bibitem{MAX6662}
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\bibitem{FTUspecs}
ETH Z{\"u}rich, IPP.
\newblock {\em FTU Firmware Specifications v3}, 2010.


\bibitem{FLD-Schematics}
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\end{thebibliography}

\end{document}