Data
Acquisition Software System
Electronics
The
data acquistion electronics is based around VME using VME adcs (Silena 9418),
tdcs (CAEN V767) and scalers (CAEN V560). There is also a custom module for overall control of the data
acquisition system which was designed and built at Daresbury.
Data
readout is via the VME bus.
The
system currently consists of 512 channels of adc and tdc with 32 scaler
channels which are housed in 2 VME crates linked by a SBS VME=>VME
interconnect. This link makes the 2 VME crates appear as 1 as far as access
from the VME control CPU is concerned.
The
data acquisition processor is a Motorola MVME2431 single width VME board
module. This contains a PowerPC 750
microprocessor running at 350 MHz with 32 Mbyte SDRAM, on-board fast
Ethernet controller and 64 bit VME interface. The LynxOS real time software
kernel is used (release 3.1.0).
LynxOS
is a UNIX like system enhanced for real-time use. The OS is initially booted
from a Sun workstation (tuda0)
but once the data acquisition software components are loaded and running
no further access to the Sun is required unless additional software components
are required by manual intervention.
All
components of the data acquisition software system are controlled and monitored
via MIDAS. Normally this will be
a session running in tuda0 but
any of the workstations can be used if needed.
This is a Sun workstation (normally tuda0)
which acts as the boot server for the data acquisition processor and runs the MIDAS
Tape Server program.
The
data read from the VME by the data acquisition processor is transmitted via
Ethernet to the Data Acquisition Server where the Tape Server program writes it
to tape (normally DLT).
The
read-out program running in the data analysis processor performs simple checks
on the data, generates statistics and builds “singles” histograms for each adc.
Online data analysis is performed by SortShell which is given access to the
event data in real time by “peeking” at the current event data buffers held
within shared memory by the tape server program.
Other
sort programs can also be used.