EPICS devSNMP Extensions

Euan Troup, Euan.Troup@csiro.au

CSIRO Australia Telescope National Facility

ASKAP Project

Paul Wild Observatory

What Is devSNMP ?

• devSNMP connects a set of objects on a network to an EPICS IOC

• SNMP is the Simple Network Management Protocol• Found in routers, switches, embedded devices etc• Provides for set, get and notification messages

• Existing version at http://www-mks2.desy.de/content/e4/e40/e41/e12212/index_ger.html

• SNMP support based on Net-SNMP API http://www.net-snmp.org

• Earlier versions of devSNMP only supported get, now supports SNMP set and notification messages (traps)

A Bit More SNMP

• SNMP objects consist of an OID and a value

• An OID is a numerical string in dotted decimal format such as .1.3.6.1.2.1.1.1

• Numeric OIDs are given a more descriptive name using MIB files• MIBS use ASN.1 to give structure to names• .1.3.6.1.2.1.1.1 becomes .iso.org.dod.internet.mgmt.mib-

2.system.sysDescr

• OID + value corresponds to EPICS PV name + value

• SNMP includes basic data types similar to EPICS data types e.g. integer, octet string…

• MIB file parsing is provided by the Net-SNMP library so you can abbreviate above to MIB-2::sysDescr

devSNMP Features And Extensions

• devSNMP 1.03 supports ai, longin, stringin, waveform, longin with support for truncated 64-bit values (Counter64 SNMP type)

• Added support for ao, longout, stringout

• Support for I/O Intr processing of trap messages• Supported directly so no need for snmptrapd config

• Overhead removed in asynch processing• Original used polling once per second per object• Now transaction only when requested• Can have updates faster than once per second

• Explicit SNMP v1 support• Compile-time option for sending float or double data types

directly over SNMP• Tested on Linux & OS X with Net-SNMP 5.4

devSNMP In Practice

• Rabbit microcontroller• Analogue and digital I/O for monitor & control• Low power mode for data acquisition – low RFI• Wakes up periodically and sends stored data via SNMP trap

• (Proposed) DC PSU monitorATCA crate 4.5 kW DC supply with SNMP monitoring

• Patched source can be provided by Euan Troup, Euan.Troup@csiro.au

• Compiles to a support library & soft IOC

• Makefile for application needs the following added:USR_CFLAGS += `net-snmp-config --cflags` USR_CFLAGS += -DNETSNMP_NO_INLINE USR_LDFLAGS += `net-snmp-config –libs`

How Do You Use It?

• Use field (DTYP,"Snmp") • Instrument I/O setup e.g. field (INP,"@localhost public IF-MIB::ifInUcastPkts.1 Counter32: 11") for ai,longin,stringin and

• Hostname of remote object• SNMP community name• MIB name to be converted to OID• Data type of object• Size of buffer for processing returned value

• Same for output records

• Add v1 to end of string for SNMP v1 support• If omitted defaults to SNMP v2c

How Do You Use It (2)?

• Record processing pass 1 through device support sets record->pact = true, puts device private info on list of active requests, starts an asynch SNMP transaction and sends an epicsEvent to asynch read thread

• Read thread waits on event which can be sent by any record then processes all outstanding requests using snmp_sess_select_info() call

• After calling select() an SNMP callback function or timeout function is triggered

• SNMP callback starts an EPICS callbackRequest() which starts record processing again and completes pass 2 through device support

How Does It Work?

• Trap support creates a separate thread listening on udp port 162 or specified using an environment variable

• Port 162 is privileged under unix so root or suid executable is required

• Records structures for records using I/O Intr scanning are put on a list which is traversed each time a trap is received

• Thread receives traps and matches hostnames and OID for active records then uses callback mechanism to process the record

• Records can be added or removed from trap processing by changing the SCAN field which uses get_ioint_info() device support function

How Does It Work (2)?

• rbv (readback value) support for ao record

• Make traps with multiple updates of database records atomic

• Full support for Counter64 – probably requires 64-bit record in EPICS

Possible Future Developments