Transcript SNMP Driver Extensions

EPICS devSNMP Extensions
Euan Troup, [email protected]
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://wwwmks2.desy.de/content/e4/e40/e41/e12212/index_ger.html
• SNMP support based on Net-SNMP API http://www.netsnmp.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.mib2.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 monitor
ATCA crate 4.5 kW DC supply with SNMP monitoring
How Do You Use It?
• Patched source can be provided by Euan Troup,
[email protected]
• 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 (2)?
• Use field (DTYP,"Snmp")
• Instrument I/O setup e.g.
field (INP,"@localhost public IFMIB::ifInUcastPkts.1 Counter32: 11") for
ai,longin,stringin and
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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 Does It Work?
• 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 (2)?
• 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
Possible Future Developments
• 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