Online Design Goals

(in preparation, probably will be reorganized, ejw, 8-aug-2007)

Overview

Below I list the overall specifications, performance requirements, and design goals, of Hall D DAQ/Online/Control systems. All groups working on the project, e.g. JLab DAQ group, JLab Electronics group, etc, must design to meet them.

I propose specifying and planning the entire project in three documents:

• Online Design Goals (this document)
• Online Major Milestones, eventually to be turned into a Gantt chart
• [[Online Work Breakdown], eventually to be turned into a Gantt chart

The first sets the overall parameters of the project. The second adds the time element to the first and specifies major deliverables without going into great detail. The third is a fine breakdown that goes into details and includes assignment of responsitilities.

Other JLab groups will develop similar documents, then they will be reconciled and additional performance milestones, etc. will be developed.

Basic Requirements from Hall D Design Report

The Hall D DAQ system will be composed of:

• trigger system
• approximately 80 front-end synchronous crates
• timing distribution system
• a dozen or so asynchronous data sources
• a few dozen additional software components that do not generate high-speed data, but need to be integrated into the run control system
• all the associated computers and software needed to:
  • configure the system
  • take data
  • build events
  • store events on local disk
  • transfer event files to permanent storage.

At turn-on Hall D will accept 10**7 photons/sec, with an expected L1 trigger rate of 18 kHz. At high luminosity the beam rate will be ten times higher, or 10**8 photons/sec, giving an expected trigger rate of 180 kHz assuming the same L1 rejection rate. With an average event size of 4 kByte the data rate off the detector at low luminosity will be 72 MByte/sec, and 720 MByte/sec at high luminosity. At low luminosity there will be no L3 rejection, and all events will be written to disk (at 72 MByte/sec). At high luminosity we expect a L3 rejection rate of a factor of 10, so the rate to disk will also be 72 MByte/sec.

Notes: All front-end DAQ boards will be pipelined to handle the high trigger rate without deadtime. Triggers and backplane interrupts must be distributed to all front-end crates. Timing distribution must be appropriate for F1TDC's, 250 MHz FADC's, 100 MHz FADC's. and perhaps a few other miscellaneous modules.

The Hall D Online and Controls systems will be composed of additional computers and other equipment needed to:

• monitor and control the Hall D detector and DAQ system
• ensure data quality
• collect meta-data
• manage storage and transfer of the raw data and associated meta-data
• etc.

DAQ Design Goals

The initial design must meet the requirements of high luminosity with the exception of the L3 farm, which at turn-on will be a small prototype, used for monitoring only. Note that at high luminosity events will be written from the L3 farm to disk, while at low luminosity they will be written from an earlier stage. Also note that during installation and testing the trigger and DAQ software must be capable of supporting multiple, simultaneous runs to allow detector groups to check out their hardware in parallel.

The DAQ design must include some headroom above the expected rates. Thus I propose the following design goals and parameters for the Hall D DAQ (numbers in parenthesis are for low luminosity):

• Accepted L1 trigger rate - 200 kHz (20 kHz)
• Average event size - 5 kByte (5 kByte)
• Data rate off detector - 1 GByte/sec (100 MByte/sec)
• Rate to L3 farm - 1 GByte/sec (20 MByte/sec at turn-on to prototype farm for monitoring)
• L3 rejection - factor of 10 (no rejection)
• Rate to local raid disk - 100 MByte/sec from L3 farm (100 MByte/sec from earlier stage)
• Rate to silo - 100 MByte/sec (100 MByte/sec)

Online/Controls Design Goals

The online and controls effort consists of developing, configuring, controlling, and/or monitoring the following:

• approximately 80 front-end crates and associated detector electronics
• a few dozen compute servers, a file server, raid system, and associated computer equipment
• L3 farm consisting of up to 200 nodes
• a 10-GBit wired and wireless networking system
• a few hundred detector control points, where e.g. a HV control point may include hundreds of actual channels
• at least one PLC, controlling the solenoid magnet and other devices
• many hundreds of alarm channels
• interface to JLab accelerator controls system
• event display
• data quality monitoring system
• archive system for monitoring and controls data
• bookkeeping system (for triggering at 200 kHz, data taking at 100 MByte/sec, and multiple/parallel running with runs lasting from a few minutes to a few days)

Since we expect the accelerator to still be using EPICS for the upgrade, the Hall D controls system must be compatible with EPICS at the level required by the Accelerator Operations group.