ICALEPCS’2005 - Geneva

ACS in ALMA 1

ACS in ALMA

Allen Farris

National Radio Astronomy Observatory

Lead, ALMA Control System

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The ALMA Project(Atacama Large Millimeter Array)

• 64 x 12m antennas , 30-950 GHz• Array configurations:150 m-14 Km• Near S. Pedro de Atacama, Chile at 5000 m• EU and North America as equal partners• Japan will add Compact Array:

12 x 7m + 4 x 12m antennas and extra correlator, receivers

• 2 prototype antennas (in Socorro, NM)• Construction phase 2003-2011• Early Science foreseen for 2009

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ALMA

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ALMA Computer Network

• In addition to non-real-time computers, ALMA will have over 82 computers that operate in real-time that may be separated by distances of 14 Km.

• ALMA makes heavy use of CORBA for distributed processing.

• Many parts of the system are in Java, but critical real-time code is in C++. Python is also used as a high-level scripting language.

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Physical Architecture

weather station

ARTMArray Real Time Machine

Maser

GPS

AM

B (

CA

N)

Correlator ControlComputer (CCC)

Correlator

64 antennas

N stations

Gb Ethernet (on fiber)

Operator Console

Disk array

Archive Processor

Array Control Computer

Quick-LookSubsystem

CalibrationSubsystem

SchedulingSubsystem

AOS (5000m)

OSF (2800m)

Raw

cor

rela

tor

data

(4M

b/s

(av)

, 40M

b/s

(pea

k)

Gb

Eth

erne

t (on

fibe

r)

Gb

Eth

erne

t (on

fibe

r)

LO Generation

High-speed switched network

100 Mbps Shared Ethernet

Antenna Control UnitACU

Antenna Based Systems

Bridge

Front-endElectronics

Nutator

ABMAntenna Bus Master

AM

B (

CA

N)

Antenna

Gb Ethernet (on fiber)

Gb

Eth

erne

t (on

fibe

r)

Dedicated fiber optic cable

MultipleAMB buses

ControlSubsystem

1 pulse/s

Correlator DataProcessor (CDP)

CA

NFPDP

Digitizers

Back-endElectronics

Switch

Switch

2 Mb/s (av), 20M

b/s (peak)

ExecutiveSubsystem

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Software Context

ObservationPreparation

Scheduling

Data ReductionPipeline

Archive

Executive

ALMA Common Software

PrincipalInvestigator

1. Create observing project

2. Store observingproject

3. Get projectdefinition

4. Dispatch scheduling block id

6. Start data reduction

8. Notify PI

7.1. Get raw data & meta-data

7.2. Store science results

9. Get projectdata

ArchiveResearcher

TelescopeOperator

f. Get science data

d. Notifyof

SpecialCondition

e. StartStop

Configure

c. Alter Schedule / Override action

Control System

Correlator

Calibration Pipeline

Quick Look Pipeline

5. Execute scheduling block

5.2 Setup correlator

5.3. Storeraw data

5.4. Storemeta-data

5.6. Store calibration results

5.7. Store quick-look results

Primary functional paths Additional functions ALMA software subsystem external agent

Real-time

a. Monitorpoints

b. Monitorpoints

5.5b. Access raw data & meta-data

h. Store admin data

g. breakpointresponse

5.5a. Access raw data & meta-data

5.1. Get SB

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Major Features of ACS

• Component/Container model

• Properties of Components

• Notification Channels

• Alarms

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Component/Container Model

• Important conceptually and architecturally: This is the major feature that allows us to manage and access objects via CORBA.

• All major software modules (a collection of classes) are components that run under the control of a container.

• The ACS Manager controls the deployment of containers throughout the network.

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Containers

• Containers are language specific: either C++, Java or Python.

• Containers manage the lifecycle of components. When a client requests the services of a component the container loads it (if it isn’t already loaded) and gives the client access to it.

• Containers provide services to components, such as logging, error handling, and access to other components.

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Components

• A component is a CORBA object with an IDL interface that is available to clients.

• Crafting a component is fairly easy: An “ordinary” class (in Java for example) is required to:– Implement certain ACS lifecycle methods required

of all components and,– Implement the public IDL methods that it makes

available to external clients.

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Use of Components and Containers in Control

• The Control system uses all three types of containers: Java, C++, and Python.

• Every antenna in ALMA has its own computer and its own container on that computer.

• Each hardware device on the antenna is represented as a component in that antenna’s container.

• In addition, the antenna itself is a component that is commanded and controlled by the Master Component that controls the entire ALMA array.

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Properties of Components

• Components may define properties.• These may be hardware device monitor points such as

the value of a voltage, temperature, frequency setting, or a state variable (busy, idle, error, etc.).

• ACS provides facilities for monitoring properties based on time intervals or other logical criteria (such as when value changes by a certain amount).

• Values of properties are gathered and stored permanently in the archive. This is a very important part of the Control system.

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Notification Channels

• Notification channels provide asynchronous communication across the ALMA network.

• Based on the publish/subscribe model: any subsystem may create a notification channel and publish events (defined using IDL structs) and any interested client may subscribe.

• Control uses two notification channels: an “external” one for communication with other subsystems and an “internal” one that is used to command antennas and other real-time components.

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Alarms

• ACS will release a new version of alarms in its 5.0 version.

• Control will make heavy use of alarms. This is very important for managing error situations.

• Example: If the temperature in an antenna back-end rises beyond some limit, the back-end devices will be shut down and the power supply turned off.

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Why have ACS?

• ACS stands for ALMA Common Software. It functions as a kind of architectural cement that unifies the system into a coherent structure.

• ACS is very important as an insulating layer between our software and CORBA.– We want our software to be as independent of CORBA as

is reasonable.

– We want to depend on CORBA concepts and be relatively independent of specific CORBA implementations.