Online Design Goals

(still working on this, ejw, 24-jul-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.

The JLab DAQ group will develop a similar document, then the two will be reconciled and dates, performance milestones, etc. will be developed. We will repeat this with other JLab groups as needed.

Basic Requirements from Hall D Design Report

The Hall D DAQ will be composed of approximately 80 front-end synchronous crates; a dozen or so asynchronous data sources; and a few dozen other software components that do not generate high-speed data, but need to be integrated into the run control system.

At turn-on Hall D will accept 10**7 photons/sec, with an expected trigger rate of 18 kHz, assuming a L1 rejection rate of 50%. 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.

All front-end DAQ boards must be pipelined to handle the high trigger rate without deadtime.

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 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)

DAQ Timelines

First beam to the hall is expected in ????, with production data taking expected to start in ????. Prototype DAQ systems for individual detector testing must be available by ????. The full DAQ must be ready for testing the complete detector with cosmic or pulser triggers by ????.

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 and 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.

Online/Controls Timelines

Online and controls systems must be ready by ???.