Channel Access Clients< kazuro.furukawa @ kek.jp >Introduction to
Channel Access Client Library
Kazuro Furukawa<kazuro.furukawa@kek.jp>

for EPICS2009 at RRCATJanuary 29, 2009
Based on presentations byKenneth Evans, Jr., 2004
Kazuro Furukawa, 2006
Kay Kasemir, 2007

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

Outline!Channel Access Concepts!Channel Access API!Simple CA Client!Simple CA Client with Callbacks!(EPICS Build System)

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

Channel Access Reference Manual!The place to go for more information!Found in the EPICS web pages"http://www.aps.anl.gov/epics/index.php"Look under Documents"Also under Base, then a specific version of BaseEPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

EPICS Overview
MEDM

MEDM

ClientClientClientMEDM

Channel Access

ServerEPICS Workshop 2009, RRCAT, India

IOC

IOC

IOC

Meter

Power Supply

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Channel Access Clients

Search and Connect Procedure
MEDM

MEDM

ClientClientClient

MEDM

3. TCP Connection
Let’s talk !
2. UDP Reply

1.

UDP Broadcast Sequence
Who has it ?

I have it !

ServerCheck

EPICS Workshop 2009, RRCAT, India

Check
IOC

IOC
Check
IOC

IOC
Check

Meter

Power Supply

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Channel Access Clients

Channel Access in One Slide“connection request” or“search request”“get” or“caGet”

Who has a PV named “
S1A:H1:CurrentAO”?

“put” or“caPut”“set amonitor”

Change its
value to 30.5

Notify me
when thevaluechanges

What is its
value?

Channel Access Client

CA Client
CA Server
Channel Access Server

I do.

Process Variables:

25.5
AMPS

OK, itis now
30.5

S1A:H1:CurrentAO“put complete”

S1:P1:xor

30.5 is too high.
It is now set tothe maximum
value of 27.5.

or

You are notauthorized tochange this value

S1:P1:yS1:G1:vacuum

EPICS Workshop 2009, RRCAT, India

It is now

It is now

It is now

20.5 AMPS

10.5 AMPS-0.0023 AMPS

“post an event”
or“post a monitor”

Kazuro Furukawa, KEK, Jan.2009.

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Search Request!A search request consists of a sequence of UDP packets"Only goes to EPICS_CA_ADDR_LIST"Starts with a small interval (30 ms), that doubles each time
"Until it gets larger than 5 s, then it stays at 5 s"Stops after 100 packets or when it gets a response"Never tries again until it sees a beacon anomaly or creates a new PV"Total time is about 8 minutes to do all 100!Servers have to do an Exist Test for each packet!Usually connects on the first packet or the first few!Non-existent PVs cause a lot of traffic"Try to eliminate them

EPICS Workshop 2009, RRCAT, India

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Beacons!A Beacon is a UDP broadcast packet sent by a Server!When it is healthy, each Server broadcasts a UDP beacon at
regular intervals (like a heartbeat)"EPICS_CA_BEACON_PERIOD, 15 s by default!When it is coming up, each Server broadcasts a startup
sequence of UDP beacons"Starts with a small interval (25 ms, 75 ms for VxWorks)"Interval doubles each time
"Until it gets larger than 15 s, then it stays at 15 s
# Takes about 10 beacons and 40 s to get to steady state!Clients monitor the beacons"Determine connection status, whether to reissue searches
EPICS Workshop 2009, RRCAT, India

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Virtual Circuit Disconnect!3.13 and early 3.14
"Hang-up message or no response from server for 30 sec.
"If not a hang-up, then client sends “Are you there” query"If no response for 5 sec, TCP connection is closed"MEDM screens go white"Clients reissue search requests!3.14 5 and later"Hang-up message from server"TCP connection is closed"MEDM screens go white"Clients reissue search requests

EPICS Workshop 2009, RRCAT, India

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Virtual Circuit Unresponsive!3.14.5 and later"No response from server for 30 sec.
"Client then sends “Are you there” query"If no response for 5 sec, TCP connection is not closed#For several hours, at least"MEDM screens go white"Clients do not reissue search requests#Helps with network storms"Clients that do not call ca_poll frequently get a virtual circuit
disconnect even though the server may be OK#Clients written for 3.13 but using 3.14 may have a problem#May be changed in future versions

EPICS Workshop 2009, RRCAT, India

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Channel Access Clients

Important Environment Variables!EPICS_CA_ADDR_LIST"Determines where to search"Is a list (separated by spaces)#“123.45.1.255 123.45.2.14 123.45.2.108”"Default is broadcast addresses of all interfaces on the host#Works when servers are on same subnet as Clients"Broadcast address#Goes to all servers on a subnet#Example: 123.45.1.255#Use ifconfig –a on UNIX to find it (or ask an administrator)!EPICS_CA_AUTO_ADDR_LIST"YES: Include default addresses above in searches"NO: Do not search on default addresses"If you set EPICS_CA_ADDR_LIST, usually set this to NO
EPICS Workshop 2009, RRCAT, India

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EPICS_CA_ADDR_LIST
MEDM

MEDM

ClientClientClientBroadcastSpecific

123.45.1.255

123.45.2.108

Subnet 1

MEDM

Subnet 2
Not Included

ServerEPICS Workshop 2009, RRCAT, India

IOC

IOC

IOC

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Channel Access Clients

Other Environment Variables!CA Client!CA Server

EPICS_CA_ADDR_LISTEPICS_CA_AUTO_ADDR_LISTEPICS_CA_CONN_TMO
EPICS_CA_BEACON_PERIODEPICS_CA_REPEATER_PORTEPICS_CA_SERVER_PORTEPICS_CA_MAX_ARRAY_BYTESEPICS_TS_MIN_WEST

EPICS_CAS_SERVER_PORTEPICS_CAS_AUTO_BEACON_ADDR_LISTEPICS_CAS_BEACON_ADDR_LISTEPICS_CAS_BEACON_PERIODEPICS_CAS_BEACON_PORTEPICS_CAS_INTF_ADDR_LISTEPICS_CAS_IGNORE_ADDR_LIST!See the Channel Access Reference Manual
for more information

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3.13 and 3.14 Similarities!Much effort has done into making clients written
for 3.13 work with 3.14 with no changes to thecoding!Even large programs like MEDM have had to makeonly a few minor changes!This means existing programs typically do notneed to be rewritten"This is good!

!In contrast, Channel Access Servers require manychanges in converting to 3.14

EPICS Workshop 2009, RRCAT, India

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3.13 and 3.14 Differences!3.14 is threaded"Your program does not have to be threaded!3.14 has different names for some functions"ca_context_create for ca_task_initialize"ca_context_destroy for ca_task_exit"ca_create_channel for ca_search_and_connect"ca_create_subscription for ca_add_event"ca_clear_subscription for ca_clear_event"The new functions may have more capabilities, usually related tothreading"We will use the new names!3.14 has a different mechanism for lost connections"Virtual circuit unresponsive (Not available in 3.13)"Virtual circuit disconnected

EPICS Workshop 2009, RRCAT, India

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Channel Access!The main CA client interface is the "C" library thatcomes with EPICS base"Internally uses C++, but API is pure C.

!Almost all other CA client interfaces use that C
library"Exception: New pure Java JAC

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Basic Procedure for a Channel Access Client!Initialize Channel Access"ca_task_initialize or ca_context_create!Search"ca_search_and_connect or ca_create_channel!Do get or put"ca_get or ca_put!Monitor"ca_add_event or ca_create_subscription!Give Channel Access a chance to work
"ca_poll, ca_pend_io, ca_pend_event!Clear a channel"ca_clear_channel!Close Channel Access"ca_task_exit or ca_context_destroy
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cadef.h!All C or C++ programs must include cadef.h"#include <cadef.h>!You can look at this file to get more insight into
Channel Access!This presentation will use C examples"We will try to emphasize concepts, not the language"Even if you do not use C, it is important to understandwhat is going on behind what you do use

EPICS Workshop 2009, RRCAT, India

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ca_context_create
enum ca_preemptive_callback_select {ca_disable_preemptive_callback,ca_enable_preemptive_callback };int ca_context_create (enum ca_preemptive_callback_select SELECT );!Should be called once prior to any other calls!Sets up Channel Access!Use SELECT=ca_disable_preemptive_callback"Unless you intend to do threads!Can also use ca_task_initialize() for 3.13 compatibility

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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ca_context_destroy
void ca_context_destroy ();!Should be called before exiting your program!Shuts down Channel Access!Can also use ca_task_exit() for 3.13
compatibility

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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ca_create_channel
typedef void caCh (struct connection_handler_args ARGS);
int ca_create_channel (const char *PVNAME,
caCh *CALLBACK,
void *PUSER,
capri PRIORITY,
chid *PCHID );!Sets up a channel and starts the search process!PVNAME is the name of the process variable!CALLBACK is the name of your connection callback (or NULL)"The callback will be called whenever the connection state changes,
including when first connected"Information about the channel is contained in ARGS
"Use NULL if you don’t need a callback
EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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ca_create_channel, cont’d
typedef void caCh (struct connection_handler_args ARGS);
int ca_create_channel (const char *PVNAME,
caCh *CALLBACK,
void *PUSER,
capri PRIORITY,
chid *PCHID );!PUSER is a way to pass additional information"Whatever you have stored at this address"It is stored in the chid
"In C++ it is often the this pointer for a class"Use NULL if you don’t need it!Use PRIORITY=CA_PRIORITY_DEFAULTEPICS Workshop 2009, RRCAT, India

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ca_create_channel, cont’d
typedef void caCh (struct connection_handler_args ARGS);
int ca_create_channel (const char *PVNAME,
caCh *CALLBACK,
void *PUSER,
capri PRIORITY,
chid *PCHID );!A chid is a pointer to (address of) an opaque struct used by Channel
Access to store much of the channel information"chanId is the same as chid (typedef chid chanId;)!PCHID is the address of the chid pointer (Use &CHID)"You need to allocate space for the chid before making the call
"Channel Access will allocate space for the struct and return the address

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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ca_create_channel, cont’d
typedef void caCh (struct connection_handler_args ARGS);
int ca_create_channel (const char *PVNAME,
caCh *CALLBACK,
void *PUSER,
capri PRIORITY,
chid *PCHID );!Use macros to access the information in the chid"ca_name(CHID) gives the process variable name"ca_state(CHID) gives the connection state"ca_puser(CHID) gives the PUSER you specified"Etc.

!The ARGS struct in the connection callback includes the chid!Can also use ca_search_and connect() for 3.13 compatibility
EPICS Workshop 2009, RRCAT, India

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ca_clear_channel
int ca_clear_channel (chid CHID);!Shuts down a channel and reclaims
resources!Should be called before exiting the program!CHID is the same chid used in
ca_create_channel

EPICS Workshop 2009, RRCAT, India

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ca_array_get
int ca_array_get (chtype TYPE,
unsigned long COUNT,
chid CHID,
void *PVALUE );!Requests a scalar or array value from a process variable!Typically followed by ca_pend_io!TYPE is the external type of your variable"Use one of the DBR_xxx types in db_access.h"E.g. DBR_DOUBLE or DBR_STRING!COUNT is the number of array elements to read
!CHID is the channel identifier from ca_create_channel!PVALUE is where you want the value(s) to go"There must be enough space to hold the values
EPICS Workshop 2009, RRCAT, India

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ca_array_get_callback
typedef void ( *pCallBack ) (struct event_handler_args ARGS);
int ca_array_get_callback (chtype TYPE,
unsigned long COUNT,
chid CHID,
pCallBack USERFUNC,
void *USERARG );!Requests a scalar or array value from a process variable,using a callback!TYPE is the external type of your variable"Use one of the DBR_xxx types in db_access.h"E.g. DBR_DOUBLE or DBR_STRING!COUNT is the number of array elements to read

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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ca_array_get_callback, cont’d
typedef void ( *pCallBack ) (struct event_handler_args ARGS);
int ca_array_get_callback (chtype TYPE,
unsigned long COUNT,
chid CHID,
pCallBack USERFUNC,
void *USERARG );!CHID is the channel identifier from ca_create_channel!USERFUNC is the name of your callback to be run when theoperation completes!USERARG is a way to pass additional information to the callback"struct event_handler_args has a void *usr member

EPICS Workshop 2009, RRCAT, India

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ca_array_put
int ca_array_put (chtype TYPE,
unsigned long COUNT,
chid CHID,
const void *PVALUE);!Requests writing a scalar or array value to a process variable!Typically followed by ca_pend_io!TYPE is the external type of your supplied variable"Use one of the DBR_xxx types in db_access.h"E.g. DBR_DOUBLE or DBR_STRING!COUNT is the number of array elements to write!CHID is the channel identifier from ca_create_channel!PVALUE is where the value(s) to be written are found

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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ca_array_put_callback
typedef void ( *pCallBack ) (struct event_handler_args ARGS);
int ca_array_put_callback (chtype TYPE,
unsigned long COUNT,
chid CHID,
const void *PVALUE,
pCallBack USERFUNC,
void *USERARG );!Requests writing a scalar or array value to a process
variable, using a callback!TYPE is the external type of your variable"Use one of the DBR_xxx types in db_access.h"E.g. DBR_DOUBLE or DBR_STRING

EPICS Workshop 2009, RRCAT, India

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ca_array_put_callback, cont’d
typedef void ( *pCallBack ) (struct event_handler_args ARGS);
int ca_array_put_callback (chtype TYPE,
unsigned long COUNT,
chid CHID,
const void *PVALUE,
pCallBack USERFUNC,
void *USERARG );!COUNT is the number of array elements to write!CHID is the channel identifier from ca_create_channel!PVALUE is where the value(s) to be written are found

EPICS Workshop 2009, RRCAT, India

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ca_array_put_callback, cont’d
typedef void ( *pCallBack ) (struct event_handler_args ARGS);
int ca_array_put_callback (chtype TYPE,
unsigned long COUNT,
chid CHID,
const void *PVALUE,
pCallBack USERFUNC,
void *USERARG );!USERFUNC is the name of your callback to be run when theoperation completes!USERARG is a way to pass additional information to the callback"struct event_handler_args has a void *usr member

EPICS Workshop 2009, RRCAT, India

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ca_create_subscription
typedef void ( *pCallBack ) (struct event_handler_args ARGS);
int ca_create_subscription (chtype TYPE,
unsigned long COUNT,
chid CHID,
unsigned long MASK,
pCallBack USERFUNC,
void *USERARG,
evid *PEVID );!Specify a callback function to be invoked whenever!theprocess variable undergoes!significant state changes"Value, Alarm status, Alarm severity"This is the way to monitor a process variable

EPICS Workshop 2009, RRCAT, India

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ca_create_subscription, cont’d
typedef void ( *pCallBack ) (struct event_handler_args ARGS);
int ca_create_subscription (chtype TYPE,
unsigned long COUNT,
chid CHID,
unsigned long MASK,
pCallBack USERFUNC,
void *USERARG,
evid *PEVID );!TYPE is the external type you want returned"Use one of the DBR_xxx types in db_access.h"E.g. DBR_DOUBLE or DBR_STRING!COUNT is the number of array elements to monitor

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

ca_create_subscription, cont’d
typedef void ( *pCallBack ) (struct event_handler_args ARGS);
int ca_create_subscription (chtype TYPE,
unsigned long COUNT,
chid CHID,
unsigned long MASK,
pCallBack USERFUNC,
void *USERARG,
evid *PEVID );!CHID is the channel identifier from ca_create_channel!MASK has bits set for each of the event trigger types requested"DBE_VALUE"DBE_LOG"DBE_ALARM

Value changes
Exceeds archival deadband
Alarm state changes

EPICS Workshop 2009, RRCAT, India

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Channel Access Clients

ca_create_subscription, cont’d
typedef void ( *pCallBack ) (struct event_handler_args ARGS);
int ca_create_subscription (chtype TYPE,
unsigned long COUNT,
chid CHID,
unsigned long MASK,
pCallBack USERFUNC,
void *USERARG,
evid *PEVID );!USERFUNC is the name of your callback to be run when the statechange occurs!USERARG is a way to pass additional information to the callback"struct event_handler_args has a void *usr member

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

ca_create_subscription, cont’d
typedef void ( *pCallBack ) (struct event_handler_args ARGS);
int ca_create_subscription (chtype TYPE,
unsigned long COUNT,
chid CHID,
unsigned long MASK,
pCallBack USERFUNC,
void *USERARG,
evid *PEVID );!PEVID is the address of an evid (event id)"You need to allocate space for the evid before making the call"Similar to a chid
"Only used to clear the subscription (Can be NULL if not needed)

EPICS Workshop 2009, RRCAT, India

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Channel Access Clients

ca_clear_subscription
int ca_clear_subscription ( evid EVID );!Used to remove a monitor callback!EVID is the evid from ca_create_subscription

EPICS Workshop 2009, RRCAT, India

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Channel Access Clientsca_add_exception_event
typedef void (*pCallback) (struct exception_handler_args ARGS );int ca_add_exception_event (pCallback USERFUNC,
void *USERARG );!Used to replace the default exception handler!USERFUNC is the name of your callback to be run whenan exception occurs"Use NULL to remove the callback!USERARG is a way to pass additional information to thecallback"struct exception_handler_args has a void *usr member

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Request Handling!The preceding routines are requests"They only queue the operation"They hardly ever fail#The return values are almost always ECA_NORMAL#(But they should be checked)!These requests are only processed when one of thefollowing is called"ca_pend_io"ca_pend_event"ca_poll

Blocks until requests are processed
Blocks a specified time
Processes current work only

!If these routines are not called, the requests are notprocessed and background tasks are also not processed!The rule is that one of these should be called every 100 ms"To allow processing of background tasks (beacons, etc.)

EPICS Workshop 2009, RRCAT, India

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ca_pend_io
int ca_pend_io (double TIMEOUT);!Flushes the send buffer!Blocks for up to TIMEOUT seconds until"Outstanding gets complete"Searches with no callback have connected!Returns ECA_NORMAL when gets and searches are complete!Returns ECA_TIMEOUT otherwise"Means something went wrong"Get requests can be reissued"Search requests can be reissued after ca_clear_channel!Channel Access background tasks are performed"Unless there were no outstanding I/O requests!Use with searches, gets, and puts that don’t use callbacks

EPICS Workshop 2009, RRCAT, India

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ca_pend_event
int ca_pend_event (double TIMEOUT);!Flushes the send buffer!Process background tasks for TIMEOUT seconds"Does not return until TIMEOUT seconds have elapsed!Use this when your application doesn’t have to
do anything else
!Use ca_pend_event instead of sleep

EPICS Workshop 2009, RRCAT, India

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ca_poll
int ca_poll ();!Flushes the send buffer!Process outstanding tasks only
"Exits when there are no more outstanding tasks#Otherwise similar to ca_pend_event!Use this when your application has other things
to do"E.g. most GUI programs!Be sure it is called at least every 100 ms

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CHID Macros
chtype ca_field_type ( CHID );unsigned ca_element_count ( CHID );char *ca_name ( CHID );void *ca_puser ( CHID );void ca_set_puser ( chid CHID, void *PUSER );enum channel_state ca_state ( CHID );enum channel_state {cs_never_conn, Valid chid, server not found or unavailable
cs_prev_conn,
Valid chid, previously connected to server
cs_conn, Valid chid, connected to server
cs_closed };Channel deleted by userchar *ca_host_name ( CHID );int ca_read_access ( CHID );int ca_write_access ( CHID );EPICS Workshop 2009, RRCAT, India

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ca_connection_handler_args
struct ca_connection_handler_args {chanId chid;
Channel idlong op;
CA_OP_CONN_UP or
CA_OP_CONN_DOWN};!Used in connection callback!Note chanId is used rather than chid"Some compilers don’t like chid chid;

EPICS Workshop 2009, RRCAT, India

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event_handler_args
typedef struct event_handler_args {void *usr;
User argument supplied with request
chanId chid;
Channel ID
long type;
The type of the item returned
long count;
The element count of the item returned
const void *dbr; A pointer to the item returned
int status;
ECA_xxx status of the requested op} evargs;!Used in get, put, and monitor callbacks!Do not use the value in dbr if status is not ECA_NORMALEPICS Workshop 2009, RRCAT, India

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Channel Access API Functions
ca_add_exception_event
ca_attach_context
ca_clear_channel
ca_clear_subscription
ca_client_status
ca_context_create
ca_context_destroy
ca_context_status
ca_create_channel
ca_create_subscription
ca_current_context
ca_dump_dbr()
ca_element_countca_field_typeca_flush_io

ca_getca_host_nameca_message
ca_nameca_read_accessca_replace_access_rights_event
ca_replace_printf_handler
ca_pend_event
ca_pend_io
ca_poll
ca_puserca_putca_set_puser
ca_signal
ca_sg_block
ca_sg_create

ca_sg_delete
ca_sg_get
ca_sg_put
ca_sg_resetca_sg_test
ca_state
ca_test_event
ca_test_io
ca_write_accesschannel_statedbr_size[]dbr_size_ndbr_value_size[]
dbr_type_to_text
SEVCHK

ca_searchca_search_and_connect

ca_task_exit
ca_task_initialize

Deprecatedca_add_event
ca_clear_event

EPICS Workshop 2009, RRCAT, India

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makeBaseApp.pl!Includes a template for basic CA client in C:"Start with this:mkdir cac ; cd cac
makeBaseApp.pl -t caClient cacApp
make"Result:
bin/linux-x86/caExample <some PV>
bin/linux-x86/caMonitor <file with PV list>"Then read the sources, compare with the reference
manual, and edit/extend to suit your needs.
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makeBaseApp's caExample.c!Minimal CA client program.
"Fixed timeout, waits until data arrives.
"Requests everything as 'DBR_DOUBLE'.
#… which results in values of C-type 'double'.
#See db_access.h header file for all the DBR_… constants
and the resulting C types or structures.
#In addition to the basic DBR_<type> requests, it ispossible to request packaged attributes like
DBR_CTRL_<type> to get { value, units, limits, …} in one
request.

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makeBaseApp's caMonitor.c!Better CA client program.
"Registers callbacks to get notified when connected
ot disconnected"Subscribes to value updates instead of waiting.
"… but still uses the same data type (DBR_STRING)
for everything.

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Ideal CA client?
!Use callbacks for everything"no idle 'wait', no fixed time outs.

!Upon connection, check the channel's native type (int,double, string, …)"to limit the type conversion burden on the IOC.

!… request the matching DBR_CTRL_<type> once
"to get the full channel detail (units, limits, …).

!… and then subscribe to DBR_TIME_<type> to get updates of
only time/status/value"so now we always stay informed, yet limit the network traffic.
" Only subscribe once, not with each connection, because CA client
library will automatically re-activate subscriptions!

!This is what EDM, archiver, … do.
"Quirk: They don't learn about online changes of channel limits, units,….
Doing that via a subscription means more network traffic, and CA
doesn't send designated events for 'meta information changed'.
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Channel Access Clients

Simple CA Client!Defines and includes/* Simple CA client */#define TIMEOUT 1.0#define SCA_OK 1#define SCA_ERR 0#define MAX_STRING 40#include <stdio.h>#include <stdlib.h>#include <string.h>#include <cadef.h>
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Channel Access Clients

Simple CA Client!Function prototypes and global variables/* Function prototypes */int main(int argc, char **argv);
static int parseCommand(int argc, char **argv);
static void usage(void);/* Global variables */int pvSpecified=0;char name[MAX_STRING];
char value[MAX_STRING];
double timeout=TIMEOUT;EPICS Workshop 2009, RRCAT, India

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Channel Access Clients

Simple CA Client!Parse the command line
int main(int argc, char **argv){
int stat;chid pCh;/* Parse the command line */if(parseCommand(argc,argv) != SCA_OK)
exit(1);if(!pvSpecified) {printf("No PV specified\n");exit(1);}EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

Simple CA Client!Initialize Channel Access/* Initialize */stat=ca_context_create(ca_disable_preemptive_callback);if(stat != ECA_NORMAL) {printf("ca_context_createfailed:\n%s\n",ca_message(stat));exit(1);}EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

Simple CA Client!Request the search/* Search */stat=ca_create_channel(name,NULL,NULL,
CA_PRIORITY_DEFAULT,&pCh);if(stat != ECA_NORMAL) {printf("ca_create_channel failed:\n%s\n",ca_message(stat));exit(1);}EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

Simple CA Client!Call ca-pend_io to process the search/* Process search */stat=ca_pend_io(timeout);
if(stat != ECA_NORMAL) {printf(“search timed out after %g sec\n",timeout);exit(1);}EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

Simple CA Client!Request the get/* Get the value */stat=ca_array_get(DBR_STRING,1,pCh,&value);if(stat != ECA_NORMAL) {printf("ca_array_get:\n%s\n",ca_message(stat));exit(1);}EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

Simple CA Client!Call ca_pend_io to process the get/* Process get */stat=ca_pend_io(timeout);
if(stat != ECA_NORMAL) {printf(“get timed out after %g sec\n",timeout);exit(1);}
printf("The value of %s is %s\n",name,value)

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Simple CA Client!Clean up/* Clear the channel */stat=ca_clear_channel(pCh);if(stat != ECA_NORMAL) {printf("ca_clear_channel failed:\n%s\n",ca_message(stat));}/* Exit */ca_context_destroy();
return(0);}EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

SEVCHK!For simple error handling in test programs"SEVCHK ( <function call>, “message” )#Macro that checks return codes#If error, displays message and aborts#Used in example programs#DON’T use for robust clients

EPICS Workshop 2009, RRCAT, India

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Channel Access Clients

Simple CA Client!Output
simplecaget evans:calc
The value of evans:calc is 6

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

Simple CA Client with Callbacks!Defines and includes/* Simple CA client with Callbacks */#define TIMEOUT 1.0#define SCA_OK 1#define SCA_ERR 0#define MAX_STRING 40#include <stdio.h>#include <stdlib.h>#include <time.h>#include <string.h>#include <cadef.h>

EPICS Workshop 2009, RRCAT, India

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Simple CA Client with Callbacks!Function prototypes/* Function prototypes */int main(int argc, char **argv);
static void connectionChangedCB(struct connection_handler_args args);
static void valueChangedCB(struct event_handler_args args);
static char *timeStamp(void);static int parseCommand(int argc, char **argv);
static void usage(void);

EPICS Workshop 2009, RRCAT, India

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Channel Access Clients

Simple CA Client with Callbacks!Global variables/* Global variables */int pvSpecified=0;char name[MAX_STRING];
time_t curTime, startTime;double timeout=TIMEOUT;EPICS Workshop 2009, RRCAT, India

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Channel Access Clients

Simple CA Client with Callbacks!Parse the command line
int main(int argc, char **argv){
int stat;chid pCh;/* Parse the command line */if(parseCommand(argc,argv) != SCA_OK) exit(1);if(!pvSpecified) {printf("No PV specified\n");exit(1);}EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

Simple CA Client with Callbacks!Initialize Channel Access/* Initialize */stat=ca_context_create(ca_disable_preemptive_callback);if(stat != ECA_NORMAL) {printf("ca_context_createfailed:\n%s\n",ca_message(stat));exit(1);}EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

67Channel Access Clients

Simple CA Client with Callbacks!Search/* Search */stat=ca_create_channel(name,connectionChangedCB,NULL,
CA_PRIORITY_DEFAULT,&pCh);if(stat != ECA_NORMAL) {printf("ca_create_channel failed:\n%s\n",ca_message(stat));exit(1);}
printf("%s Search started for %s\n",timeStamp(),name);

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

68Channel Access Clients

Simple CA Client with Callbacks!Wait in ca_pend_event for the callbacks to occur/* Wait */startTime=curTime;
ca_pend_event(timeout);
printf("%s ca_pend_event timed out after %g sec\n",timeStamp(),timeout);

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Simple CA Client with Callbacks!Clean up/* Clear the channel */stat=ca_clear_channel(pCh);if(stat != ECA_NORMAL) {printf("ca_clear_channel failed:\n%s\n",ca_message(stat));}/* Exit */ca_context_destroy();
return(0);}EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Simple CA Client with Callbacks!Connection callback implementation
static void connectionChangedCB(structconnection_handler_args args){
chid pCh=args.chid;
int stat;/* Branch depending on the state */switch(ca_state(pCh)) {EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

71Channel Access Clients

Simple CA Client with Callbacks!Connection callback implementationcase cs_conn:
printf("%s Connection successful\n",timeStamp());
stat=ca_array_get_callback(DBR_STRING,1,pCh,
valueChangedCB,NULL);
if(stat != ECA_NORMAL) {printf("ca_array_get_callback:\n%s\n",ca_message(stat));exit(1);}break;EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

Simple CA Client with Callbacks!Connection callback implementationcase cs_never_conn:
printf("%s Cannot connect\n",timeStamp());
break;
case cs_prev_conn:
printf("%s Lost connection\n",timeStamp());
break;
case cs_closed:
printf("%s Connection closed\n",timeStamp());
break;}}EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Simple CA Client with Callbacks!Value changed callback implementation
static void valueChangedCB(struct
event_handler_args args){/* Print the value */if(args.status == ECA_NORMAL && args.dbr) {printf("%s Value is: %s\n",timeStamp(),(char *)args.dbr);
printf("Elapsed time: %ld sec\n",curTime-startTime);}}
EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

74Channel Access Clients

Simple CA Client with Callbacks!Output
simplecagetcb evans:calc
Sep 14 18:31:55 Search started for evans:calc
Sep 14 18:31:55 Connection successful
Sep 14 18:31:55 Value is: 5
Elapsed time: 0 sec
Sep 14 18:31:56 ca_pend_event timed out after 1
sec!Time for this operation is typically a few ms

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

Source files for Simple Get Clients!Some of the code that is not related to Channel
Access has not been shown!All the files necessary to build a project as an
EPICS Extension should be available with thepresentation"Makefile"Makefile.Host"simplecaget.c"simplecagetcb.c"LICENSE!Stored as simpleCA.tar.gz
EPICS Workshop 2009, RRCAT, India

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Channel Access Clients

EPICS Build System!Supports both native and GNU compilers!Builds multiple types of components"libraries, executables, headers, scripts, java classes, …

!Supports multiple host and target operating systems!Builds for all hosts and targets in a single <top> tree
"epics/base"epics/extensions!Allows sharing of components across <top> trees!Has different rules and syntax for 3.13 and 3.14

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Channel Access Clients

System Requirements!Required software"Perl version 5 or greater"GNU make, version 3.78.1/3.81 or greater"C++ compiler and linker (GNU or host vendor's
compiler)!Optional software"Tornado II and board support packages"RTEMS development tools and libraries"Motif, X11, JAVA, Tcl/Tk, Python…
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Channel Access ClientsUser Requirements!Set an environment variable to specify thearchitecture"EPICS_HOST_ARCH for 3.14
#solaris-sparc, linux-x86, win32-x86, darwin-ppc, etc.

"HOST_ARCH for 3.13
#solaris, Linux, WIN32, etc.

!Set the PATH so the required components can be
found"Perl, GNU make, C and C++ compilers"System commands (e.q. cp, rm, mkdir)

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

79Channel Access Clients

Some Pointers to Documents!Example files"http://www.aps.anl.gov/epics/"Documents - Training - Developing Client Tools- Introduction to Chnnael Access Clients- Example Files!Build examples of EPICS-Base, etc
on several Platforms"http://www-linac.kek.jp/jk/win32/"http://www-linac.kek.jp/jk/linux/"http://www-linac.kek.jp/jk/darwin/
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Some Examples of Channel-Access!Of course, this Presentation!makeBaseApp.pl -t caClient {app-name}"caExample.c"caMonitor.c!makeBaseEx.pl -t example {ext-name}!caExample.c

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

Typical Extensions Build Tree
epics/base<top> for base
epics/extensions<top> for extensions
config3.13 configuration
configure3.14 configurationbin
Binaries by architecturesolarissolaris-sparc
lib
Libraries by architecturesolarissolaris-sparc
src
Sources by application
simpleCA
Application source files
O.solaris
Binaries for this application
O.solaris-sparc
EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

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Channel Access Clients

Getting Started with an Extension!Make a directory structure for base
http://www.aps.anl.gov/epics/extensions/index.php"E.g. epics/base!Obtain base and build it"Set COMPAT_TOOLS_313 first if necessary (see later)!Make a directory structure for extensions"E.g. epics/extensions!Get extensions/config and configure from the EPICS pages!Set EPICS_BASE to your desired version of base"In extensions/config/RELEASE for 3.13
"In extensions/configure/RELEASE for 3.14

!Type gnumake (or make) in extensions!Get an extension and put it under extensions/src!Type gnumake (or make) in your application directory
EPICS Workshop 2009, RRCAT, India

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83Channel Access Clients

Using the 3.13 Build Rules for Extensions!Most existing extensions are still set up for 3.13 builds"There is a Makefile and a Makefile.Host"Makefile.Host is most important and has 3.13 syntax"Can still use a 3.14 base

!Set HOST_ARCH for your platform"solaris, Linux, WIN32, etc.

!Set EPICS_HOST_ARCH for your platform"solaris-sparc, linux-x86, win32-x86, darwin-ppc, etc.

!Configuration is in extensions/config"RELEASE (Specifies what base to use, can be 3.14)"CONFIG_SITE_xxx (Specifies local changes for xxx arch)!Before building a 3.14 base"Modify base/configure/CONFIG_SITE#COMPAT_TOOLS_313 = YES

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

84Channel Access Clients

Using the 3.14 Build Rules for Extensions!Go to the the EPICS page for your version of base"http://www.aps.anl.gov/epics/base/index.php!Read the README"It is very extensive"Should tell you everything you need to know

!There is a only a Makefile and it uses 3.14 syntax!Set EPICS_HOST_ARCH for your platform"solaris-sparc, linux-x86, win32-x86, darwin-ppc, etc.

!Configuration is in extensions/configure"RELEASE (Specifies what base)"os/CONFIG_SITE_xxx (Specifies local changes for xxx arch)

EPICS Workshop 2009, RRCAT, India

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Channel Access Clients

Makefile for Simple Get Clients
TOP = ../..
include $(TOP)/config/CONFIG_EXTENSIONS
include $(TOP)/config/RULES_ARCHSEPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

86Channel Access Clients

Makefile.Host for Simple Get Clients
TOP = ../../..
include $(TOP)/config/CONFIG_EXTENSIONSHOST_OPT = NO
CMPLR = STRICTPROD = simplecaget simplecagetcb
PROD_LIBS = ca Com
ca_DIR = $(EPICS_BASE_LIB)
Com_DIR = $(EPICS_BASE_LIB)
simplecaget_SRCS += simplecaget.c
simplecagetcb_SRCS += simplecagetcb.c
include $(TOP)/config/RULES.Host
EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

87Channel Access Clients

Acknowledgements!Jeff Hill [LANL] is responsible for EPICS Channel
Access and has developed almost all of it himself!Janet Anderson [ANL] is responsible for and has
developed most of the EPICS Build System

EPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

88Channel Access ClientsThank YouEPICS Workshop 2009, RRCAT, India

Kazuro Furukawa, KEK, Jan.2009.

89