EPICS R3.14 Channel Access Reference Manual
Jeffrey O. Hill
Los Alamos National Laboratory
SNS Division
Copyright Experimental Physics and Industrial Control
System (EPICS) Copyright, 1995, The University of California, The University
of Chicago Portions of this material resulted from work developed under a
U.S. Government contract and are subject to the following license: For a
period of five years from March 30, 1993, the Government is granted for
itself and others acting on its behalf a paid-up, nonexclusive, irrevocable
worldwide license in this computer software to reproduce, prepare derivative
works, and perform publicly and display publicly. Upon request of Licensee,
and with DOE and Licensors approval, this period may be renewed for two
additional five year periods. Following the expiration of this period or
periods, the Government is granted for itself and others acting on its
behalf, a paid-up, nonexclusive, irrevocable worldwide license in this
computer software to reproduce, prepare derivative works, distribute copies
to the public, perform publicly and display publicly, and to permit others to
do so. NEITHER THE UNITED STATES NOR THE UNITED STATES DEPARTMENT OF ENERGY,
NOR ANY OF THEIR EMPLOYEES, MAKES ANY WARRANTY, EXPRESS OR IMPLIED, OR
ASSUMES ANY LEGAL LIABILITY OR RESPONSIBILITY FOR THE ACCURACY, COMPLETENESS,
OR USEFULNESS OF ANY INFORMATION, APPARATUS, PRODUCT, OR PROCESS DISCLOSED,
OR REPRESENTS THAT ITS USE WOULD NOT INFRINGE PRIVATELY OWNED RIGHTS. Initial
development by: The Controls and Automation Group (AOT-8), Ground Test
Accelerator, Accelerator Technology Division, Los Alamos National Laboratory.
Co-developed with: The Controls and Computing Group, Accelerator Systems
Division, Advanced Photon Source, Argonne National Laboratory.
Last modified $Date: 2001/11/20 16:35:25 $
Table of Contents
Functionality Index
Deprecated Function Call Interface Function Index
Configuration
Why Reconfigure Channel Access
Typically reasons to reconfigure EPICS Channel Access:
- Two independent control systems must share a network without fear of
interaction
- A test system must not interact with an operational system
- Use of address lists instead of broadcasts for name resolution and
server beacons
- Control system occupies multiple IP subnets
- Nonstandard client disconnect time outs or server beacon intervals
- Specify the local time zone
- Transport of large arrays
All Channel Access (CA) configuration occurs through EPICS environment
variables. When searching for an EPICS environment variable EPICS first looks
in the environment using the ANSI C getenv() call. If no matching variable
exists then the default specified in the EPICS build system configuration
files is used.
Name |
Range |
Default |
EPICS_CA_ADDR_LIST |
{N.N.N.N N.N.N.N ...} |
<none> |
EPICS_CA_AUTO_ADDR_LIST |
{YES, NO} |
YES |
EPICS_CA_CONN_TMO |
r > 0.1 seconds |
30.0 |
EPICS_CA_BEACON_PERIOD |
r > 0.1 seconds |
15.0 |
EPICS_CA_REPEATER_PORT |
i > 5000 |
5065 |
EPICS_CA_SERVER_PORT |
i > 5000 |
5064 |
EPICS_CA_MAX_ARRAY_BYTES |
i >= 16384 |
16384 |
EPICS_TS_MIN_WEST |
-720 < i <720 minutes |
360 |
Environment variables are set differently depending on the command line
shell that is in use.
C shell |
setenv EPICS_CA_ADDR_LIST 1.2.3.4 |
bash |
export EPICS_CA_ADDR_LIST=1.2.3.4 |
vxWorks shell |
putenv ( "EPICS_CA_ADDR_LIST =1.2.3.4" ) |
DOS command line |
set EPICS_CA_ADDR_LIST=1.2.3.4 |
Windows NT / 2000 / XP |
control panel / system / environment tab |
CA and Wide Area Networks
Normally in a local area network (LAN) environment CA discovers the
address of the host for an EPICS process variable by broadcasting frames
containing a list of channel names ( CA search messages ) and waiting for
responses from the servers that host the channels identified. Likewise CA
clients efficiently discover that CA servers have recently joined the LAN or
disconnected from the LAN by monitoring periodically broadcasted beacons sent
out by the servers. Since hardware broadcasting requires special hardware
capabilities, we are required to provide additional configuration information
when EPICS is extended to operate over a wide area network (WAN).
Channel Access is implemented using internet protocols (IP). IP addresses
are divided into host and network portions. The boundary between each portion
is determined by the IP netmask. Portions of the IP address corresponding to
zeros in the netmask specify the hosts address within an IP subnet. Portions
of the IP address corresponding to binary ones in the netmask specify the
address of a host's IP subnet. Normally the scope of a broadcasted frame will
be limited to one IP subnet. Addresses with the host address portion set to
all zeros or all ones are special. Modern IP kernel implementations reserve
destination addresses with the host portion set to all ones for the purpose
of addressing broadcasts to a particular subnet. In theory we can issue a
broadcast frame on any broadcast capable LAN within the interconnected
internet by specifying the proper subnet address combined with a host portion
set to all ones. In practice these "directed broadcasts" are frequently
limited by the default router configuration. The proper directed broadcast
address required to reach a particular host can be obtained by logging into
that host and typing the command required by your local operating
environment. Ignore the loop back interface and use the broadcast address
associated with an interface connected to a path through the network to your
client. Typically there will be only one Ethernet interface.
UNIX |
ifconfig -a |
vxWorks |
ifShow |
Windows |
ipconfig |
IP ports are positive integers. The IP address, port number, and protocol
type uniquely identify the source and destination of a particular frame
transmitted between computers. Servers are typically addressed by a well
known port number. Clients are assigned a unique ephemeral port number during
initialization. IP ports below 1024 are reserved for servers that provide
standardized facilities such as mail or file transfer. Port number between
1024 and 5000 are typically reserved for ephemeral port number
assignments.
Typically vxWorks hosts boot with routes configured for the host's subnet.
If a EPICS system is operating in a WAN environment it may be necessary to
configure routes into the vxWorks system which enable a vxWorks based CA
server to respond to requests originating outside it's subnet. An EPICS
system manager can limit access to a particular host by not providing routes
in that host that reach outside of a limited set of subnets.
routeShow() |
hostAdd "the-router", "N.N.N.N" |
routeAdd "0","the-router" |
During initialization CA builds a list of the destination addresses used
when sending CA client name resolution (search) requests, and when sending CA
server beacons. This table is initialized by traversing a database of network
interfaces attached to the host. For each interface found that is attached to
a broadcast capable IP subnet the broadcast address of that subnet is added
to the list. For each point to point interface found the destination address
of that link is added to the list. This network interface introspection
driven initialization is disabled only if the EPICS environment variable
"EPICS_CA_AUTO_ADDR_LIST" exists and its value is either of "no" or "NO". The
typical default is to enable network interface introspection driven
initialization with "EPICS_CA_AUTO_ADDR_LIST" set to "YES" or "yes".
Following network interface introspection, any IP addresses specified in
the EPICS environment variable EPICS_CA_ADDR_LIST are added to the list of
destination addresses for CA client name resolution requests and CA server
beacons. In a multiple subnet EPICS system users will quickly learn that the
EPICS_CA_ADDR_LIST must be set so that CA name resolution ( search requests )
frames pass from CA clients to the targeted CA servers. However, a more
subtle configuration mistake resulting in wasted network bandwidth will be to
not also arrange for beacons issued by the targeted CA servers to reach the
hosts of all potential clients. For this reason the EPICS_CA_ADDR_LIST
environment variable parameter will often be identical within a group of
clients and servers that communicate between themselves. The addresses in
EPICS_CA_ADDR_LIST may be dotted IP addresses or host names if the local OS
has support for host name to IP address translation. When multiple names are
added to EPICS_CA_ADDR_LIST they must be separated by while space. There is
no requirement that the addresses specified in the EPICS_CA_ADDR_LIST be a
broadcast addresses, but this will often be the most convenient choice.
C shell |
setenv EPICS_CA_ADDR_LIST "1.2.3.255 8.9.10.255" |
bash |
export EPICS_CA_ADDR_LIST="1.2.3.255 8.9.10.255" |
vxWorks |
putenv ( "EPICS_CA_ADDR_LIST=1.2.3.255 8.9.10.255" ) |
IP port numbers
The two IP port numbers used by Channel Access may be configured. This
might occur when a site decides to set up two or more completely independent
control systems that will share the same network. For instance, a site might
set up an operational control system and a test control system on the same
network. In this situation it is desirable for the test system and the
operational system to use identical PV names without fear of collision.
Usually the best choice is to assign new port numbers to the operational
system and allow the test system to use the default CA port numbers. A site
might also configure the CA port numbers because some other facility has
already reserved the defaults.
Purpose |
Default |
Environment Variable |
CA Server |
5064 |
EPICS_CA_SERVER_PORT |
CA Beacons (sent to CA repeater daemon) |
5065 |
EPICS_CA_REPEATER_PORT |
If the CA client library does not see a beacon from a server that it is
connected to for EPICS_CA_CONN_TMO seconds then an echo message is sent to
the server over TCP/IP. If this echo message isn't promptly replied to then
the client will assume that the server is no longer present on the network
and disconnect. Disconnecting implies notification of client side application
programs. The parameter EPICS_CA_CONN_TMO is specified in floating point
seconds. The default is typically 15.0 seconds.
When a CA server initializes it sends "beacon" messages to each address
specified in EPICS_CA_ADDR_LIST, and also any addresses auto configured from
network interfaces found, with a short period between "beacons". However,
this period is doubled each time that a "beacon" is sent until a plateau
specified by EPICS_CA_BEACON_PERIOD is reached. This parameter is specified
in floating point seconds. For efficient operation it is recommended that
EPICS_CA_BEACON_PERIOD be set to at least one half of the value specified for
EPICS_CA_CONN_TMO.
Starting with EPICS R3.14 all of the libraries in the EPICS base
distribution rely on facilities built into the operating system to determine
the time zone. Nevertheless, several programs commonly used with EPICS use
the original "tssubr" library and therefore they still rely on proper
configuration of EPICS_TS_MIN_WEST.
While the CA client library does not translate in between the local time
and the time zone independent internal storage of EPICS time stamps, many
EPICS client side applications call core EPICS libraries which provide these
services. To set the correct time zone users must compute the number of
positive minutes west of GMT (maximum 720 inclusive) or the negative number
of minutes east of GMT (minimum -720 inclusive). This integer value is then
placed in the variable EPICS_TS_MIN_WEST.
Time Zone |
EPICS_TS_MIN_WEST |
USA Eastern |
300 |
USA Central |
360 |
USA Mountain |
420 |
USA Pacific |
480 |
Alaska |
540 |
Hawaii |
600 |
Japan |
-540 |
Germany |
-120 |
United Kingdom |
-60 |
The environment variable EPICS_CA_MAX_ARRAY_BYTES determines the size of
the largest array that may pass through CA. This parameter must be set
appropriately for both the CA client and the CA server. In EPICS R3.14 CA
maintains a free list of 16384 byte network buffers that are used for
ordinary communication. If EPICS_CA_MAX_ARRAY_BYTES is larger than 16384
then a second free list of larger data buffers is established when clients
request transportation of large arrays.
Name |
Range |
Default |
EPICS_CAS_ADDR_LIST |
{N.N.N.NN.N.N.N...} |
<none> |
EPICS_CAS_SERVER_PORT |
i > 5000 |
|
EPICS_CAS_BEACON_ADDR_LIST |
{N.N.N.NN.N.N.N...} |
|
EPICS_CAS_BEACON_PORT |
i > 5000 |
|
The server must build a list of addresses to send beacons to. If
EPICS_CA_AUTO_ADDR_LIST has the value "YES" then the beacon address list will
contain at least the broadcast address of all LAN interfaces found in the
host and the destination address of all point-to-point interfaces found in
the host. If EPICS_CAS_BEACON_ADDR_LIST is defined then its contents will be
used to augment this list. Otherwise, if EPICS_CA_ADDR_LIST is define its
contents will be used to augment this list.
Function Call Interface General Guidelines
If successful, the routines described here return the status code
ECA_NORMAL. Unsuccessful status codes returned from the client library are
listed with each routine in this manual. Operations that appear to be valid
to the client can still fail in the server. Writing the string "off" to a
floating point field is an example of this type of error. If the server for a
channel is located in a different address space than the client then the
ca_xxx() operations that communicate with the server returns status
indicating the validity of the request and whether it was successfully
enqueued to the server.
Significant performance gains may be realized if we don't wait for a
response to return from the server after each request. All requests which
require interaction with a CA server are accumulated (buffered) and not
forwarded to the IOC until one of ca_flush_io, ca_pend_io, ca_pend_event, or
ca_sg_pend are called allowing several operations to be efficiently sent over
the network together. Any process variable values written into your program's
variables by ca_get() should not be referenced by your program until
ECA_NORMAL has been received from ca_pend_io().
All arguments of type chtype expect one of the set of DBR_XXXX. These
constants, defined in db_access.h, enumerate which of the standard data types
you wish to transfer. There are data types for all of the C primitive types
and there are also compound types that include various process variable
properties such as units, limits, time stamp, or alarm status.
Certain CA client initiated requests asynchronously execute an application
supplied call back in the client when a response arrives. The functions
ca_put_callback, ca_get_callback, and ca_add_event all request notification
of asynchronous completion via this mechanism. The structure
"event_handler_args" is passed to the application supplied callback. In this
structure the field "dbr" is a void pointer to any data that might be
returned. The field "status" will be set to one of the CA error codes in
caerr.h and will indicate the status of the operation performed in the IOC.
If the status field isn't set to ECA_NORMAL or data isn't normally returned
from the operation (i.e. put call back) then you should expect that the field
"dbr" will be set to NULL. The fields "usr", "chid", "type", and "count" are
set to the values specified when the operation was initiated by the
application.
struct event_handler_args {
void *usr; /* user argument supplied when event added */
chid chid; /* channel id */
long type; /* dbr type of the value returned */
long count; /* element count of the item(s) returned */
void *dbr; /* pointer to the value returned */
int status; /* ECA_XXX status of the op from server */
};
When the server detects a failure, and there
is no client call back function attached to the request, then an exception
handler is executed in the client. The default exception handler prints a
message on the console and exits if the exception condition is severe. To
modify this behavior see ca_add_exception_event().
If the server for the channel and the client are located on the same node
then the ca_xxx() operations bypass the server and directly interact with the
server tool (the IOC's database). Therefore, the ca_XXX() routines always
return the status of the operation directly to the caller with no opportunity
for asynchronous notification of failure via an exception handler.
Certain routines have arguments that specify an address at which channel
access is to write a value of type DBR_XXXX. Care should be taken to ensure
that you have reserved space of sufficient size. Architecture independent
types are provided in db_access.h to assist programmers in writing portable
code. For example "dbr_short_t" should be used to send or receive type
DBR_SHORT. The dbr type size returning MACROS provided in db_access.h may
also be used.
For routines that require an argument specifying the number of array
elements, no more than the process variable's maximum native element count
may be requested. The process variable's maximum native element count is
available from ca_element_count() when the channel is connected. If less
elements than the process variable's native element count are requested the
requested values will be fetched beginning at element zero. By default CA
limits the number of elements in an array to be no more than approximately
16k divided by the size of one element in the array. Starting with EPICS
R3.14 the maximum array size may be configured in the client and in the
server.
Channel connections through the network are inherently transient. Channels
are always initially assumed to be disconnected. A connection state change
call back function may be installed to be run whenever a channel connects or
disconnects. If a connection state change call back function is not installed
(if a nil function pointer is supplied) then the user must wait for
successful status from ca_pend_io prior to using the channel for the first
time. Once the channel connects the user can freely perform IO operations
through the channel, but he should expect that the channel might disconnect
at any time due to network interruptions or server restarts. Otherwise, if a
connection state change call back function is supplied, one of the arguments
to this function distinguishes between connect and disconnect events. If a
connection state change call back function is installed on a particular
channel by the user ca_pend_io will not block for the channel to connect. The
user's connection state change function will be run immediately when the
channel is created if the CA client and the server are both hosted in the
same address space (IOC).
Starting with EPICS R3.14 the CA client libraries are fully thread safe on
all OS (in past releases the library was thread safe only on vxWorks). When
the client library is initialized the programmer may specify if preemptive
call back is enabled. Preemptive call back is disabled by default. If
preemptive call back is enabled then the user's call back functions might be
called by CA's auxiliary threads when the main initiating channel access
thread is not inside of a function in the channel access client library.
Otherwise, the user's call back functions will be called only when the main
initiating channel access thread is executing inside of the CA client
library.
If preemptive call back is not enabled, then for proper operation CA must
periodically be polled to take care of background activity. This requires
that your application must either wait in one of ca_pend_event(),
ca_pend_io(), or ca_sg_block() or alternatively it must call ca_poll() every
100 milli-seconds.
When CA invokes a user's call back function it will always wait for the
callback to run to completion prior to executing another call back
function.
The error number and the error severity are embedded in CA status (error)
constants. Applications shouldn't test the success of a CA function call by
checking to see if the returned value is zero as is the UNIX convention.
Below are several methods to test CA function returns. See ca_signal() on
page 24 for more information on this topic.
status = ca_XXXX();
SEVCHK( status, "ca_XXXX() returned failure status");
if ( status & CA_M_SUCCESS ) {
printf ( "The requested ca_XXXX() operation didn't complete successfully\n");
}
if ( status != ECA_NORMAL ) {
printf("The requested ca_XXXX() operation didn't complete successfully because \"%s\"\n",
ca_message ( status ) );
}
With the embryonic releases of EPICS it was a common practice to examine a
channel's connection state, its native type, and its native element count by
directly accessing fields in a structure using a pointer stored in type
chid . Likewise, a user private pointer in the per channel
structure was also commonly set by directly accessing fields in the channel
structure. A number of difficulties arise from this practice, which has long
since been deprecated. For example, in release 3.13 it was recognized that
transient changes in certain private fields in the per channel structure
would make it difficult to reliably test the channels connection state using
these private fields directly. Therefore, in release 3.13 the names of
certain fields were changed to discourage this practice. Starting with
release 3.14 codes written this way will not compile. Codes intending to
maintain the highest degree of portability over a wide range of EPICS
versions should be especially careful. For example you should replace all
instances off channel_id->count with
ca_element_count(channel_id) . This approach should be reliable
on all versions of EPICS in use today. The construct ca_puser(chid) =
xxxx is particularly problematic. The best mechanisms for setting the
per channel private pointer will be to pass the user private pointer in when
creating the channel. This approach is implemented on all versions.
Otherwise, you can also use ca_set_puser(CHID,PUSER) , but this
function is available only after the first official (post beta) release of
EPICS 3.13.
Function Call Reference
#include <cadef.h>
enum ca_preemptive_callback_select
{ ca_disable_preemptive_callback, ca_enable_preemptive_callback };
int ca_context_create ( enum ca_preemptive_callback_select SELECT );
Description
This function should be called once prior to making any of the other
channel access calls.
Arguments
SELECT
Specifies if preemptive calback is allowed. If it is allowed your
callbacks might be called when the thread that calls this routine is
not executing in the CA client library. Programmers who are unfamiliar
with mutual exclusion locking in a multi-threaded environment should
specify ca_disable_preemptive_callback.
Returns
ECA_NORMAL - Normal successful completion
ECA_ALLOCMEM - Failed, unable to allocate space in pool
See Also
ca_context_destroy()
#include <cadef.h>
void ca_context_destroy();
Description
Shut down a channel access client context and free any resources
allocated. On most operating systems this is performed automatically at
process exit.
Returns
ECA_NORMAL - Normal successful completion
See Also
ca_context_create()
#include <cadef.h>
typedef void ( *pCallBack ) (
struct connection_handler_args );
int epicsShareAPI ca_create_channel
(
const char *PROCESS_VARIABLE_NAME,
caCh *USERFUNC,
void *PUSER,
capri priority,
chid *PCHID
);
Description
This function creates a CA channel. The CA client library will attempt to
establish and maintain a virtual circuit between the caller's application and
a named process variable in a CA server. Each call to ca_create_channel
allocates resources in the CA client library and potentially also a CA
server. The function ca_clear_channel() is used to release these resources.
If successful, the routine writes a channel identifier into the user's
variable of type "chid". This identifier can be used with any channel access
call that operates on a channel.
The circuit may be initially connected or disconnected depending on the
state of the network and the location of the channel. A channel will
only enter a connected state after server's address is determined, and only
if channel access successfully establishes a virtual circuit through the
network to the server. Channel access routines that send a request to a
server will return ECA_DISCONNCHID if the channel is currently
disconnected.
There are two ways to obtain asynchronous notification when a channel
enters a connected state.
- The first and simplest method requires that you call ca_pend_io(), and
wait for successful completion, prior to using a channel that was created
specifying a nil connection call back function pointer.
- The second method requires that you register a connection handler by
supplying a valid connection callback function pointer. This connection
handler is called whenever the connection state of the channel changes.
If you have installed a connection handler then ca_pend_io() will
not block waiting for the channel to enter a connected
state.
The function ca_state(CHID) can be used to test the connection state of a
channel. Valid connections may be isolated from invalid ones with this
function if ca_pend_io() times out.
Due to the inherently transient nature of network connections the order of
connection call backs relative to the order that ca_create_channel() calls
are made by the application can't be guaranteed, and application programs may
need to be prepared for a connected channel to enter a disconnected state at
any time.
If ca_disable_preemptive_callback is specified then
additional threads are not allowed to join the CA context using
ca_context_attach() because allowing other threads to join implies that CA
callbacks will be called preemptively from more than one thread.
Arguments
PROCESS_VARIABLE_NAME
A nil terminated process variable name string. EPICS process
control function block database variable names are of the form
"<record name>.<field name>". If the field name and the
period separator are omitted then the "VAL" field is implicit. For
example "RFHV01" and "RFHV01.VAL" reference the same EPICS process
control function block database variable.
USERFUNC
Optional address of the user's call back function to be run when
the connection state changes. Casual users of channel access may decide
to set this field to nil or 0 if they do not need to have a call back
function run in response to each connection state change event.
PUSER
The value of this void pointer argument is retained in
storage associated with the specified channel. See the MACROS manual
page for reading and writing this field. Casual users of channel access
may wish to set this field to nil or 0.
PRIORITY
- The priority level for dispatch within the server or network with 0
specifying the lowest dispatch priority and 99 the highest. This
parameter currently does not impact dispatch priorities within the
client, but this might change in the future. The abstract priority
range specified is mapped into an operating system specific range of
priorities within the server. This parameter is ignored if the server
is running on a network or operating system that does not have native
support for prioritized delivery or execution respectively.
PCHID
- The user supplied channel identifier storage is overwritten with a
channel identifier if this routine is successful.
Returns
ECA_NORMAL - Normal successful completion
ECA_BADTYPE - Invalid DBR_XXXX type
ECA_STRTOBIG - Unusually large string
ECA_ALLOCMEM - Unable to allocate memory
ca_clear_channel()
#include <cadef.h>
int ca_clear_channel (evid CHID);
Description
Shutdown and reclaim resources associated with a channel created by
ca_create_channel().
All remote operation requests such as the above are accumulated (buffered)
and not forwarded to the IOC until one of ca_flush_io, ca_pend_io,
ca_pend_event, or ca_sg_pend are called. This allows several requests to be
efficiently sent over the network in one message.
Clearing a channel does not cause its disconnect handler to be called, but
clearing a channel does shutdown and reclaim any channel state change event
subscriptions (monitors) registered with the channel.
Arguments
CHID
Identifies the channel to delete.
Returns
ECA_NORMAL - Normal successful completion
ECA_BADCHID - Corrupted CHID
#include <cadef.h>
int ca_put ( chtype TYPE,
chid CHID, void *PVALUE );
int ca_array_put ( chtype TYPE,
unsigned long COUNT,
chid CHID, const void *PVALUE);
typedef void ( *pCallBack ) ( struct event_handler_args );
int ca_put_callback ( chtype TYPE,
chid CHID, const void *PVALUE,
pCallBack PFUNC, void *USERARG );
int ca_array_put_callback ( chtype TYPE,
unsigned long COUNT,
chid CHID, const void *PVALUE,
pCallBack PFUNC, void *USERARG );
Description
Write a scalar or array value to a process variable.
When ca_array_put or ca_put are invoked the client will receive no
response unless the request can not be fulfilled in the server. If
unsuccessful an exception handler is run on the client side. If a connection
is lost and then resumed outstanding ca_array_put or ca_put requests are
not automatically reissued following reconnect, and no additional
notification are provided to the user for each put request.
When ca_array_put_callback are invoked the user supplied asynchronous call
back is called only after the initiated write operation and all actions
resulting from the initiating write operation complete. If unsuccessful the
call back function is invoked indicating bad status. If the channel
disconnects before a put callback request can be completed, then the client's
call back function is called with bad status, but this does not gaurantee
that the server did not receive and process the request before it
disconnected.
All put requests are accumulated (buffered) and not forwarded to the IOC
until one of ca_flush_io, ca_pend_io, ca_pend_event, or ca_sg_pend are calle.
This allows several requests to be efficiently combined into one message.
Arguments
TYPE
The external type of the supplied value to be written. Conversion
will occur if this does not match the native type. Specify one from the
set of DBR_XXXX in db_access.h
COUNT
Element count to be written to the specified channel. This must
match the array pointed to by PVALUE.
CHID
Channel identifier
PVALUE
Pointer to a value or array of values provided by the application
to be written to the channel.
PFUNC
address of user supplied function to be run when the requested
operation completes
USERARG
pointer sized variable retained and then passed back to user
supplied function above
Returns
ECA_NORMAL - Normal successful completion
ECA_BADCHID - Corrupted CHID
ECA_BADTYPE - Invalid DBR_XXXX type
ECA_BADCOUNT - Requested count larger than native element count
ECA_STRTOBIG - Unusually large string supplied
ECA_NOWTACCESS - Write access denied
ECA_ALLOCMEM - Unable to allocate memory
See Also
ca_flush_io()
ca_pend_event()
ca_get()
#include <cadef.h>
int ca_get ( chtype TYPE,
chid CHID, void *PVALUE );
int ca_array_get ( chtype TYPE, unsigned long COUNT,
chid CHID, void *PVALUE );
typedef void ( *pCallBack ) ( struct event_handler_args );
int ca_get_callback ( chtype TYPE,
chid CHID, pCallBack USERFUNC, void *USERARG);
int ca_array_get_callback ( chtype TYPE, unsigned long COUNT,
chid CHID,
pCallBack USERFUNC, void *USERARG );
Description
Read a scalar or array value from a process variable.
When ca_get or ca_array_get are invoked the returned channel value cant be
assumed to be stable in the application supplied buffer until after
ECA_NORMAL is returned from ca_pend_io. If a connection is lost outstanding
get requests are not automatically reissued following reconnect.
When ca_get_callback or ca_array_get_callback are invoked a value is read
from the channel and then the user's callback is invoked with a pointer to
the retrieved value. Note that ca_pend_io will not block for the delivery of
values requested by ca_get_callback. If the channel disconnects before a get
callback request can be completed, then the clients call back function is
called with bad status.
All get requests are accumulated (buffered) and not forwarded to the IOC
until one of ca_flush_io, ca_pend_io, ca_pend_event, or ca_sg_pend are
called. This allows several requests to be efficiently sent over the network
in one message.
Arguments
TYPE
The external type of the user variable to return the value into.
Conversion will occur if this does not match the native type. Specify
one from the set of DBR_XXXX in db_access.h
COUNT
Element count to be read from the specified channel. Must match
the array pointed to by PVALUE.
CHID
Channel identifier
PVALUE
Pointer to an application supplied buffer where the current value
of the channel is to be written.
USERFUNC
Address of user supplied function to be run when the requested
operation completes.
USERARG
Pointer sized variable retained and then passsed back to user
supplied call back function above.
Returns
ECA_NORMAL - Normal successful completion
ECA_BADTYPE - Invalid DBR_XXXX type
ECA_BADCHID - Corrupted CHID
ECA_BADCOUNT - Requested count larger than native element count
ECA_GETFAIL - A local database get failed
ECA_NORDACCESS - Read access denied
ECA_ALLOCMEM - Unable to allocate memory
See Also
ca_pend_io()
ca_pend_event()
ca_add_event()
#include <cadef.h>
typedef void ( *pCallBack ) (
struct event_handler_args );
int ca_add_event( chtype TYPE, chid CHID,
pCallBack USERFUNC, void *USERARG,
evid *PEVID);
int ca_add_array_event( chtype TYPE,
unsigned long COUNT, chid CHID,
pCallBack USERFUNC, void *USERARG,
double RESERVED, double RESERVED,
double RESERVED, evid *PEVID );
int ca_add_masked_array_event ( chtype TYPE,
unsigned long COUNT, chid CHID,
pCallBack USERFUNC, void *USERARG,
double RESERVED, double RESERVED, double RESERVED,
evid *PEVID, unsigned long MASK );
Description
Reguister a state change subscription and specify a call back function to
be invoked whenever the process variable undergoes significant state changes.
A significant change can be a change in the process variable's value, alarm
status, or alarm severity. In the process control function block database the
deadband field determines the magnitude of a significant change for for the
process variable's value.
Subscriptions may be installed or canceled against both connected and
disconnected channels. The specified USERFUNC is always called once
immediately after establishing each new connection with the process variable
or immediately from within ca_add_event() if the client and server share the
same address space.
If a subscription is installed on a channel in a disconnected state then
the requested count will be set to the native maximum element count of the
channel if the requested count is larger.
All subscription requests such as the above are accumulated (buffered) and
not forwarded to the IOC until one of ca_flush_io, ca_pend_io, ca_pend_event,
or ca_sg_pend are called. This allows several requests to be efficiently sent
over the network in one message.
If at any time after subscribing, read access to the specified process
variable is lost, then the call back will be invoked immediately indicating
that read access was lost via the status argument. When read access is
restored normal event processing will resume starting always with at
least one update indicating the current state of the channel.
A better name for this function might have been ca_subscribe.
Arguments
TYPE
- The type of value presented to the call back funstion. Conversion
will occur if it does not match native type. Specify one from the set
of DBR_XXXX in db_access.h
COUNT
- The element count to be read from the specified channel. A count of
zero specifies the native elemnt count.
CHID
- channel identifier
USRERFUNC
- Address of user supplied callback function to be invoked with each
subscription update
USERARG
- pointer sized variable retained and passed back to user callback
function
RESERVED
- Reserved for future use. Specify 0.0 to remain upwardly
compatible.
PEVID
- This is a pointer to user supplied event id which is overwritten if
successful. This event id can later be used to clear a specific
event. This option may may be omitted by passing a nil pointer.
MASK
- A mask with bits set for each of the event trigger types requested.
The event trigger mask must be a logical or of one or more of the
following constants.
- DBE_VALUE - Trigger events when the channel value exceeds the
monitor dead band
- DBE_LOG - Trigger events when the channel value exceeds the
archival dead band
- DBE_ALARM - Trigger events when the channel alarm state
changes.
For functions above that do not include a trigger specification,
events will be triggered when there are significant changes in the
channel's value or when there are changes in the channel's alarm state.
This is the same as "DBE_VALUE | DBE_ALARM."
Returns
ECA_NORMAL - Normal successful completion
ECA_BADCHID - Corrupted CHID
ECA_BADTYPE - Invalid DBR_XXXX type
ECA_ALLOCMEM - Unable to allocate memory
ECA_ADDFAIL - A local database event add failed
See Also
ca_pend_event()
ca_flush_io()
ca_clear_event()
#include <cadef.h>
int ca_clear_event ( evid EVID );
Description
Cancel a subscription.
All ca_clear_event() requests such as the above are accumulated (buffered)
and not forwarded to the server until one of ca_flush_io, ca_pend_io,
ca_pend_event, or ca_sg_pend are called. This allows several requests to be
efficiently sent together in one message.
Arguments
- EVID
event id returned by ca_add_event()
Returns
ECA_NORMAL - Normal successful completion
ECA_BADCHID - Corrupted CHID SEE ALSO ca_add_event()
#include <cadef.h>
int ca_pend_io ( double TIMEOUT );
Description
This function flushes the send buffer and then blocks until outstanding ca_get requests complete, and until channels created
specifying nill connection handler function pointers connect for the first
time.
- If ECA_NORMAL is returned then it can be safely assumed that all
outstanding ca_get requests have completed
successfully and channels created specifying nill connection handler
function pointers have connected for the first time.
- If ECA_TIMEOUT is returned then it must be assumed for all previous ca_get requests and properly qualified first time
channel connects have failed.
If ECA_TIMEOUT is returned then get requests may be reissued followed by a
subsequent call to ca_pend_io(). Specifically, the function will block only
for outstanding outstanding ca_get requests issued, and
also any channels created specifying a nill connection handler function
pointer, after the last call to ca_pend_io() or ca client context creation
whichever is later. Note that ca_create_channel requests should not be
reissued unless ca_clear_channel is called
first.
If no ca_get or connection state change events are
outstanding then ca_pend_io() will flush the send buffer and return
immediately without processing any outstanding channel access background
activities.
The delay specified to ca_pend_io() should take into account worst case
network delays such as Ethernet collision backoff and retransmission.
Arguments
- TIMEOUT
- Specifies the time out interval. A
TIMEOUT interval of
zero specifies forever.
Returns
ECA_NORMAL - Normal successful completion
ECA_EVDISALLOW - Function inappropriate for use within an event handler
See Also
ca_get()
ca_create_channel()
ca_test_io()
#include <cadef.h>
int ca_test_io();
Description
This function tests to see if all ca_get requests
are complete and channels created specifying a nill connection callback
function pointer are connected. It will report the status of outstanding ca_get requests issued, and channels created specifying a
nill connection callback function pointer, after the last call to
ca_pend_io() or CA context initialization whichever is later.
Returns
ECA_IODONE - All IO operations completed
ECA_IOINPROGRESS - IO operations still in progress
See Also
ca_pend_io()
#include <cadef.h>
int ca_pend_event ( double TIMEOUT );
int ca_poll ();
Description
When ca_pend_event is invoked the send buffer is flushed and CA background
activity is processed for TIMEOUT seconds.
When ca_poll is invoked the send buffer is flushed and any outstanding CA
background activity is processed.
The routine will not return before the time-out expires and all unfinished
channel access labor has been processed.
Arguments
TIMEOUT
- The duration to block in this routine in seconds. A timeout of zero
seconds blocks forever.
Returns
ECA_NORMAL - Normal successful completion
ECA_TIMEOUT - The operation timed out
ECA_EVDISALLOW - Function inappropriate for use within a call back
handler
#include <cadef.h>
int ca_flush_io();
Description
Flush outstanding IO requests to the server. This routine might be useful
to users who need to flush requests prior to performing client side labor in
parallel with labor performed in the server.
Outstanding requests are also sent whenever the buffer which holds them
becomes full.
Returns
ECA_NORMAL - Normal successful completion
ca_signal()
#include <cadef.h>
int ca_signal ( long CA_STATUS, const char * CONTEXT_STRING );
void SEVCHK( CA_STATUS, CONTEXT_STRING );
Description
Provide the error message character string associated with the supplied
channel access error code and the supplied error context to diagnostics. If
the error code indicates an unsuccessful operation a stack dump is printed,
if this capability is available on the local operating system, and execution
is terminated.
SEVCHK is a macro envelope around ca_signal which only calls ca_signal()
if the supplied error code indicates an unsuccessful operation. SEVCHK is the
recommended error handler for simple applications which do not wish to write
code testing the status returned from each channel access call.
Examples
status = ca_context_create (...);
SEVCHK ( status, "Unable to create a CA client context" );
If the application only wishes to print the message associated with an
error code or test the severity of an error there are also functions provided
for this purpose.
Arguments
CA_STATUS
The status (error code) returned from a channel access
function.
CONTEXT_STRING
A null terminated character string to supply as error context to
diagnostics.
Returns
ECA_NORMAL - Normal successful completion
#include <cadef.h>
typedef void (*pCallback) ( struct exception_handler_args HANDLERARGS );
int ca_add_exception_event ( pCallback USERFUNC, void *USERARG );
Description
Replace the currently installed exception handler call back.
When an error occurs in the server asynchronous to the clients thread then
information about this type of error is passed from the server to the client
in an exception message. When the client receives this exception message an
exception handler callbackis called.The default exceptionhandler printsa
diagnostic message on the client's standard out and terminates execution if
the error condition is severe.
Note that certain fields in "struct exception_handler_args" are not
applicable in the context of some error messages. For instance, a failed get
will supply the address in the client taskwhere thereturned value
wasrequested tobe written. For other failed operations the value of the addr
field should not be used.
Arguments
USERFUNC
Addressof usercall back functionto beexecuted when exceptions
occur. Passing a nil value causes the default exception handler to be
reinstalled.
USERARG
pointer sized variable retained and passed back to user function
above
Example
void ca_exception_handler (
struct exception_handler_args args)
{
char buf[512];
char *pName;
if ( args.chid ) {
pName = ca_name ( args.chid );
}
else{
pName = "?";
}
sprintf ( buf,
"%s - with request chan=%s op=%d data type=%s count=%d",
args.ctx, pName, args.op, dbr_type_to_text ( args.type ), args.count );
ca_signal ( args.stat, buf );
}
ca_add_exception_event ( ca_exception_handler , 0 );
Returns
ECA_NORMAL - Normal successful completion
#include <cadef.h>
typedef int caPrintfFunc ( const char *pFromat, va_list args );
int ca_replace_printf_handler ( caPrintfFunc *PFUNC );
Description
Replace the default handler for formatted diagnostic message output. The
default handler uses fprintf to send messages to 'stderr'.
Arguments
PFUNC
The address of a user supplied call back handler to be invoked
when CA prints diagnostic messages. Installing a nil pointer will cause
the default call back handler to be reinstalled.
Examples
int my_printf ( char *pformat, va_list args ) {
int status;
status = vfprintf( stderr, pformat, args);
return status;
}
status = ca_replace_printf_handler ( my_printf );
SEVCHK ( status, "failed to install my printf handler" );
Returns
ECA_NORMAL - Normal successful completion
#include <cadef.h>
typedef void ( *pCallBack )( struct access_rights_handler_args );
int ca_replace_access_rights_event ( chid CHAN, pCallBack PFUNC );
Description
Install or replace the access rights state change call back handler for
the specified channel.
The call back handler is called in the following situations.
- whenever CA connects the channel immediately before the channel's
connection handler is called
- whenever CA disconnects the channel immediately after the channel's
disconnect call back is called
- once immediately after installation if the channel is connected.
- whenever the access rights state of a connected channel changes
When a channel is created no access rights handler is installed.
Arguments
CHAN
The channel identifier.
PFUNC
Address of user supplied call back function. A nil pointer
uninstalls the current handler.
Returns
ECA_NORMAL - Normal successful completion
See Also
ca_modify_user_name()
ca_modify_host_name()
#include <cadef.h>
chtype ca_field_type ( CHID );
Description
Return the native type in the server of the process variable.
Arguments
CHID
channel identifier
Returns
TYPE
The data type code will be a member of the set of DBF_XXXX in
db_access.h. The constant TYPENOTCONN is returned if the channel is
disconnected.
ca_element_count()
#include <cadef.h>
unsigned ca_element_count ( CHID );
Description
Return the maximum array element count in the server for the specified IO
channel.
Arguments
CHID
channel identifier
Returns
COUNT
The maximum array element count in the server. An element count
of zero is returned if the channel is disconnected.
#include <cadef.h>
char * ca_name ( CHID );
Description
Return the name provided when the supplied channel id was
created.
Arguments
CHID
channel identifier
Returns
PNAME
The channel name. The string returned is valid as long as the
channel specified exists.
ca_set_puser()
#include <cadef.h>
void ca_set_puser ( chid CHID, void *PUSER );
Description
Set a user private void pointer variable retained with each channel for
use at the users discretion.
Arguments
- CHID
channel identifier
- PUSER
user private void pointer
#include <cadef.h>
void * ca_puser ( CHID );
Description
Return a user private void pointer variable retained with each channel for
use at the users discretion.
Arguments
CHID
channel identifier
Returns
PUSER
user private pointer
/* channel connection state */
#include <cadef.h>
enum channel_state {
cs_never_conn, /* valid chid, server not found or unavaliable */
cs_prev_conn, /* valid chid, previously connected to server */
cs_conn, /* valid chid, connected to server */
cs_closed }; /* channel deleted by user */
enum channel_state ca_state ( CHID );
Description
Returns an enumerated type indicating the current state of the specified
IO channel.
Arguments
CHID
channel identifier
Returns
STATE
the conection state
#include <cadef.h>
const char * ca_message ( STATUS );
Description
return a message character string corresponding to a user specified CA
status code.
Arguments
STATUS
a CA status code
Returns
- STR
ING
the corresponding error message string
#include <cadef.h>
char * ca_host_name ( CHID );
Description
Return a character string which contains the name of the host to which a
channel is currently connected.
Arguments
CHID
the channel identifier
Returns
STRING
The process variable server's host name. If the channel is
disconnected the string "<disconnected>" is returned.
#include <cadef.h>
int ca_read_access ( CHID );
Description
Returns boolean true if the client currently has read access to the
specified channel and boolean false otherwise.
Arguments
CHID
the channel identifier
Returns
STRING
boolean true if the client currently has read access to the
specified channel and boolean false otherwisex
#include <cadef.h>
int ca_write_access ( CHID );
Description
Returns boolean true if the client currently has write access to the
specified channel and boolean false otherwise.
Arguments
CHID
the channel identifier
Returns
STRING
boolean true if the client currently has write access to the
specified channel and boolean false otherwise
#include <db_access.h>
extern unsigned dbr_size[/*TYPE*/];
Description
An array that returns the size in bytes for a DBR_XXXX type.
Arguments
TYPE
The data type code. A member of the set of DBF_XXXX in
db_access.h.
Returns
SIZE
the size in bytes of the specified type
#include <db_access.h>
unsigned dbr_size_n ( TYPE, COUNT );
Description
Returns the size in bytes for a DBR_XXXX type with COUNT elements. If the
DBR type is a structure then the value field is the last field in the
structure. If COUNT is greater than one then COUNT-1 elements are appended to
the end of the structure so that they can be addressed as an array through a
pointer to the value field.
Arguments
TYPE
The data type
COUNT
The element count
Returns
SIZE
the size in bytes of the specified type with the specified number
of elements
#include <db_access.h>
extern unsigned dbr_value_size[/* TYPE */];
Description
The array dbr_value_size[TYPE] returns the size in bytes for the value
stored in a DBR_XXXX type. If the type is a structure the size of the value
field is returned otherwise the size of the type is returned.
Arguments
TYPE
The data type code. A member of the set of DBF_XXXX in
db_access.h.
Returns
SIZE
the size in bytes of the value field if the type is a structure
and otherwise the size in bytes of the type
#include <cadef.h>
Description
void ca_test_event ( struct event_handler_args );
A built-in subscription update call back handler for debugging purposes
that prints diagnostics to standard out.
Examples
void ca_test_event ();
status = ca_add_event ( type, chid, ca_test_event, NULL, NULL );
SEVCHK ( status, .... );
See Also
ca_add_event()
#include <cadef.h>
int ca_sg_create ( CA_SYNC_GID *PGID );
Description
Create a synchronous group and return an identifier for it.
A synchronous group can be used to guarantee that a set of channel access
requests have completed. Once a synchronous group has been created then
channel access get and put requests may be issued within it using ca_sg_get()
and ca_sg_put() respectively. The routines ca_sg_block() and ca_sg_test() can
be used to block for and test for completion respectively. The routine
ca_sg_reset() is used to discard knowledge of old requests which have timed
out and in all likelihood will never be satisfied.
Any number of asynchronous groups can have application requested
operations outstanding within them at any given time.
Arguments
PGID
Pointer to a user supplied CA_SYNC_GID.
Examples
CA_SYNC_GID gid;
status = ca_sg_create ( &gid );
SEVCHK ( status, Sync group create failed );
Returns
ECA_NORMAL - Normal successful completion
ECA_ALLOCMEM - Failed, unable to allocate memory
See Also
ca_sg_delete()
ca_sg_block()
ca_sg_test()
ca_sg_reset()
ca_sg_put()
ca_sg_get()
#include <cadef.h>
int ca_sg_delete ( CA_SYNC_GID GID );
Description
Deletes a synchronous group.
Arguments
- GID
Identifier of the synchronous group to be deleted.
Examples
CA_SYNC_GID gid;
status = ca_sg_delete ( gid );
SEVCHK ( status, Sync group delete failed );
Returns
ECA_NORMAL - Normal successful completion
ECA_BADSYNCGRP - Invalid synchronous group
See Also
ca_sg_create()
#include <cadef.h>
int ca_sg_block ( CA_SYNC_GID GID, double timeout );
Description
Flushes the send buffer and then waits until outstanding requests complete
or the specified time out expires. At this time outstanding requests include
calls to ca_sg_array_get() and calls to ca_sg_array_put(). If ECA_TIMEOUT is
returned then failure must be assumed for all outstanding queries. Operations
can be reissued followed by another ca_sg_block(). This routine will only
block on outstanding queries issued after the last call to ca_sg_block(),
ca_sg_reset(), or ca_sg_create() whichever occurs later in time. If no
queries are outstanding then ca_sg_block() will return immediately without
processing any pending channel access activities.
Values written into your program's variables by a channel access
synchronous group request should not be referenced by your program until
ECA_NORMAL has been received from ca_sg_block(). This routine will process
pending channel access background activity while it is waiting.
Arguments
- GID
Identifier of the synchronous group.
Examples
CA_SYNC_GID gid;
status = ca_sg_block(gid);
SEVCHK(status, Sync group block failed);
Returns
ECA_NORMAL - Normal successful completion
ECA_TIMEOUT - The operation timed out
ECA_EVDISALLOW - Function inappropriate for use within an event handler
ECA_BADSYNCGRP - Invalid synchronous group
See Also
ca_sg_test()
ca_sg_reset()
#include <cadef.h>
int ca_sg_test ( CA_SYNC_GID GID )
Description
Test to see if all requests made within a synchronous group have
completed.
Arguments
GID
Identifier of the synchronous group.
Description
Test to see if all requests made within a synchronous group have
completed.
Examples
CA_SYNC_GID gid;
status = ca_sg_test ( gid );
Returns
ECA_IODONE - IO operations completed
ECA_IOINPROGRESS - Some IO operations still in progress
#include <cadef.h>
int ca_sg_reset ( CA_SYNC_GID GID )
Description
Reset the number of outstanding requests within the specified synchronous
group to zero so that ca_sg_test() will return ECA_IODONE and ca_sg_block()
will not block unless additional subsequent requests are made.
Arguments
GID
Identifier of the synchronous group.
Examples
CA_SYNC_GID gid;
status = ca_sg_reset(gid);
Returns
ECA_NORMAL - Normal successful completion
ECA_BADSYNCGRP - Invalid synchronous group
#include <cadef.h>
int ca_sg_array_put ( CA_SYNC_GID GID, chtype TYPE,
unsigned long COUNT, chid CHID, void *PVALUE );
Write a value, or array of values, to a channel and increment the
outstanding request count of a synchronous group.
All remote operation requests such as the above are accumulated (buffered)
and not forwarded to the server until one of ca_flush_io(), ca_pend_io(),
ca_pend_event(), or ca_sg_pend() are called. This allows several requests to
be efficiently sent in one message.
If a connection is lost and then resumed outstanding puts are not
reissued.
Arguments
GID
synchronous group identifier
TYPE
The type of supplied value. Conversion will occur if it does not
match the native type. Specify one from the set of DBR_XXXX in
db_access.h.
COUNT
element count to be written to the specified channel - must match
the array pointed to by PVALUE
CHID
channel identifier
PVALUE
A pointer to an application supplied buffer containing the value
or array of valuesReturns
Returns
ECA_NORMAL - Normal successful completion
ECA_BADSYNCGRP - Invalid synchronous group
ECA_BADCHID - Corrupted CHID
ECA_BADTYPE - Invalid DBR_XXXX type
ECA_BADCOUNT - Requested count larger than native element count
ECA_STRTOBIG - Unusually large string supplied
ECA_PUTFAIL - A local database put failed
See Also
ca_flush_io()
#include <cadef.h>
int ca_sg_array_get ( CA_SYNC_GID GID,
chtype TYPE, unsigned long COUNT,
chid CHID, void *PVALUE );
Description
Read a value from a channel and increment the outstanding request count of
a synchronous group.
The values written into your program's variables by ca_sg_get should not
be referenced by your program until ECA_NORMAL has been received from
ca_sg_block , or until ca_sg_test returns ECA_IODONE.
All remote operation requests such as the above are accumulated (buffered)
and not forwarded to the server until one of ca_flush_io, ca_pend_io,
ca_pend_event, or ca_sg_pend are called. This allows several requests to be
efficiently sent in one message.
If a connection is lost and then resumed outstanding gets are not
reissued.
Arguments
GID
Identifier of the synchronous group.
TYPE
External type of returned value. Conversion will occur if this
does not match native type. Specify one from the set of DBR_XXXX in
db_access.h
COUNT
Element count to be read from the specified channel. It must match
the array pointed to by PVALUE.
CHID
channel identifier
PVALUE
Pointer to application supplied buffer that is to contain the
value or array of values to be returned
Returns
ECA_NORMAL - Normal successful completion
ECA_BADSYNCGRP - Invalid synchronous group
ECA_BADCHID - Corrupted CHID
ECA_BADCOUNT - Requested count larger than native element count
ECA_BADTYPE - Invalid DBR_XXXX type
ECA_GETFAIL - A local database get failed
See Also
ca_pend_io()
ca_flush_io()
ca_get_callback()
int ca_client_status ( unsigned level );
Description
Prints information about the client context including, at higher intereest
levels, status for each channel.
Arguments
LEVEL
The interest level. Increasing level produces increasing
detail.
struct ca_client_context * ca_current_context ();
Description
Returns a pointer to the current thread's CA context. If none then nil is
returned.
See Also
ca_attach_context()
int ca_attach_context (struct ca_client_context *CONTEXT);
Description
Become a member of the specified CA context. If
ca_disable_preemptive_callback is specified when ca_context_create()
is called ( or if ca_task_initialize() is called ) then additional threads
are not allowed to join the CA context because allowing other
threads to join implies that CA callbacks will be called preemptively from
more than one thread.
Arguments
CONTEXT
A pointer to the CA context to join with.
Returns
ECA_ISATTACHED - already attached to a CA context
See Also
ca_current_context()
acctst <PV name> [channel duplication count] [test repetition count]
Description
Channel Access Client Library regression test.
Test failure is indicated if the program stops prior to printing "test
complete". If unspecified, the channel duplication count is 20000. If
unspecified, the test repetition count is once only.
catime <PV name> [channel count] [append number to pv name if true]
Description
Channel Access Client Library performance test.
If unspecified, the channel count is 10000. If the "append number to pv
name if true" argument is specified and it is greater than zero then the
channel names in the test are numbered as follows.
<PV name>000000, <PV name>000001, ... <PV name>nnnnnn
casw
Description
CA server "beacon anomaly" logging.
CA server beacon anomalies occur when a new server joins the network, a
server is rebooted, network connectivity to a server is reestablished, or if
a server's CPU exits a CPU load saturated state.
CA clients with unresolved channels reset their search request schedualing
timers whenever they see a beacon anomaly.
This program can be useful to verify that configuration problems have not
resulted in false beacon anomalies that might cause CA to use unnecessary
additional network bandwidth and server CPU load when searching for
unresolved channels.
caEventRate <PV name>
Description
Subscribe to the specified PV and periodically log its event rate.
ca_test <PV name> [value to be written]
Description
If a value is specified it is written to the PV. Next, the current value
of the PV is converted to each of the many external data type that can be
specified at the CA client library interface, and each of these is formated
and then output to the console.
- ECA_NORMAL
- normal successful completion
- ECA_ALLOCMEM
- unable to allocate memory
- ECA_BADTYPE
- invalid DBR_XXXX type
- ECA_STRTOBIG
- unusually large string supplied
- ECA_BADCHID
- ivalid channel identifier
- ECA_BADCOUNT
- requested count larger than native element count
- ECA_PUTFAIL
- a write request failed in the server
- ECA_GETFAIL
- a read request faile din the server
- ECA_ADDFAIL
- unable to instal subscription request
- ECA_TIMEOUT
- requested operation timed out
- ECA_EVDISALLOW
- function called was inappropriate for use within a callback
function
- ECA_IODONE
- IO operations completed
- ECA_IOINPROGRESS
- some IO operations still in progress
- ECA_BADSYNCGRP
- invalid synchronous group identifier
- ECA_NORDACCESS
- read access denied
- ECA_NOWTACCESS
- write access denied
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