NB: This manual documents a 20+ year old version of EPICS, see here for the EPICS 7 Record Reference documentation.
EPICS Record Reference Manual
Advanced Photon Source
Argonne National Laboratory
The Wait record is derived from the Calc record with the following additional features:
scan parameters
read parameters
expression-related parameters
desired output parameters
write parameters
operator parameters
monitor parameters
run-time and simulation mode parameters
I/O Intr
will enable this feature. For the current EPICS release, an additional module, caMonitor.o
, must be compiled and loaded with the wait record support to provide this feature.
Note: Because of the event driven nature of this feature, it is quite easy to configure a database that results in an infinite loop which uses all available CPU time. If the wait record is set to process as a result of a channel changing and the processing of the wait record causes the channel to change again, an infinite loop will result. The symptom will be a loss of all channel access connections (lower priority tasks) even though the shell responds normally. Using the spy vxWorks utility will confirm the predicament by showing 0% free CPU time. |
Scanning Specification, Chapter 1, 1, explains how the rest of these fields are used. They are listed in Scan Fields, Chapter 2, 2.
Unlike the Calc record, these input links can be modified during run time. These are ASCII fields which have a special processing routine attached to them. When changed, the routine is called. The record will use the new link the next time the record is processed.
A consequence of reassignable links is that one cannot force the processing of any specified records prior to retrieving the data from them (i.e. there is no .PP flag). This should be considered when designing a database using the Wait record.
In this initial version, the reassignable links do not support channel access connections external to the IOC. Until this feature is added, the specified Process Variables must reside on the same IOC.
See Address Specification, Chapter 1, 2, for information on specifying links and constants.
Field | Summary | Type | DCT | Initial | Access | Modify | Rec Proc Monitor |
---|---|---|---|---|---|---|---|
INAN | Input Link A Name | STRING[40] | Yes | 0 | Yes | Yes | Yes |
INBN | Input Link B Name | STRING[40] | Yes | 0 | Yes | Yes | Yes |
INCN | Input Link C Name | STRING[40] | Yes | 0 | Yes | Yes | Yes |
INDN | Input Link D Name | STRING[40] | Yes | 0 | Yes | Yes | Yes |
INEN | Input Link E Name | STRING[40] | Yes | 0 | Yes | Yes | Yes |
INFN | Input Link F Name | STRING[40] | Yes | 0 | Yes | Yes | Yes |
INGN | Input Link G Name | STRING[40] | Yes | 0 | Yes | Yes | Yes |
INHN | Input Link H Name | STRING[40] | Yes | 0 | Yes | Yes | Yes |
ININ | Input Link I Name | STRING[40] | Yes | 0 | Yes | Yes | Yes |
INJN | Input Link J Name | STRING[40] | Yes | 0 | Yes | Yes | Yes |
INKN | Input Link K Name | STRING[40] | Yes | 0 | Yes | Yes | Yes |
INLN | Input Link L Name | STRING[40] | Yes | 0 | Yes | Yes | Yes |
The CALC field is actually converted to opcode and stored as a reverse polish expression, or postfix expression, in the RPCL field. It is this expression which is actually used to calculate VAL. CALC can be changed at run-time, and the special record routine calls a function to convert it to the postfix expression. One difference between the Calc record and the Wait record is that the Wait record contains a flag field (CLCV) that indicates if the expression is a valid one. It will be true (non-zero) if the expression is invalid, in which case an error message is generated.
The reverse polish calculation is evaluated most efficiently during run-time. The range of expressions supported by the calculation record are separated into operands, algebraic operations, trigonometric operations, relational operations, logical operations, parentheses and commas, and the question mark operator.
Field | Summary | Type | DCT | Initial | Access | Modify | Rec Proc Monitor | PP |
---|---|---|---|---|---|---|---|---|
CALC | Calculation | DBF_STRING | Yes | 0 | Yes | Yes | Yes | Yes |
RPCL | Reverse Polish | DBF_NOACCESS | No | 0 | No | No | N/A | No |
Field | Summary | Type | DCT | Initial | Access | Modify | Rec Proc Monitor |
---|---|---|---|---|---|---|---|
A | Input Values A | DOUBLE | No | 0 | Yes | Yes/No | Yes |
B | Input Values B | DOUBLE | No | 0 | Yes | Yes/No | Yes |
C | Input Values C | DOUBLE | No | 0 | Yes | Yes/No | Yes |
D | Input Values D | DOUBLE | No | 0 | Yes | Yes/No | Yes |
E | Input Values E | DOUBLE | No | 0 | Yes | Yes/No | Yes |
F | Input Values E | DOUBLE | No | 0 | Yes | Yes/No | Yes |
G | Input Values G | DOUBLE | No | 0 | Yes | Yes/No | Yes |
H | Input Values H | DOUBLE | No | 0 | Yes | Yes/No | Yes |
I | Input Values I | DOUBLE | No | 0 | Yes | Yes/No | Yes |
J | Input Values J | DOUBLE | No | 0 | Yes | Yes/No | Yes |
K | Input Values K | DOUBLE | No | 0 | Yes | Yes/No | Yes |
L | Input Values L | DOUBLE | No | 0 | Yes | Yes/No | Yes |
The comma is supported when used to separate the arguments of a binary function.
(condition)? True result : False result
A + B
(A + B) < (C + D)
(A+B)<(C+D)?E:F
(A+B)<(C+D)?E
A&B
In the desired output location (DOLN) field, the user specifies a link from which the record will retrieve the value that it writes (if the DOPT field specifies DOLD). The value is retrieved and placed in the desired output location data field (DOLD). If DOLN specifies no link, a flag field indicates that the DOLN field is invalid. When the DOLN field is invalid, the value of DOLD can be set via dbPuts at run-time.
Field | Summary | Type | DCT | Initial | Access | Modify | Rec Proc Monitor | PP |
---|---|---|---|---|---|---|---|---|
DOLN | Desired Output Location | STRING [40] | Yes | Null | Yes | Yes | No | No |
DOLD | Desired Output Location Data | DOUBLE | Yes | 0 | Yes | Yes | Yes | No |
Use VAL
in the Data Option (DOPT) field, then the value in VAL will be written. If the user specifies Use DOL
, the value retrieved from the DOLN link and contained in the DOLD field will be written. The DOPT field can be changed during run-time.The Output Link Name (OUTN) specifies where the record is to write the output value.
The Wait record does not have to write its output every time the record processes. This allows "downstream" processing of records to be done conditionally. The record has output execution options which can be specified in the OOPT field. These options are as follows.
Every Time
: Outputs are executed every time the record processes.
On Change
: Outputs are executed if the result of the calculation (VAL) is different than the previous time the record was processed.
When Zero
: Outputs are executed if the result of the calculation is zero.
When Non-zero
: Outputs are executed if the result of the calculation is not zero.
Transition To Zero
: Outputs are executed if the result of the calculation is zero and the previous value was not zero.
Transition To Non-zero
: Outputs are executed if the result of the calculation is not zero and the previous value was zero.
Field | Summary | Type | DCT | Initial | Access | Modify | Rec Proc Monitor | PP |
---|---|---|---|---|---|---|---|---|
OOPT | Output Option | RECCHOICE | Yes | 0 | Yes | Yes | No | No |
OUTN | Output Link Name | STRING [40] | Yes | Null | Yes | Yes | No | No |
DOPT | Data Option | RECCHOICE | Yes | 0 | Yes | Yes | No | No |
OEVT | Output Event | USHORT | Yes | 0 | Yes | Yes | No | No |
The HOPR and LOPR fields set the upper and lower display limits for the VAL field. The get_graphic_double
retrieves these fields.
The PREC field determines the floating point precision with which to display VAL. It is used whenever the get_precision
record support routine is called.
See Chapter 2, Fields Common to All Record Types, for more on the record name (NAME) and description (DESC) fields.
Field | Summary | Type | DCT | Initial | Access | Modify | Rec Proc Monitor | PP |
---|---|---|---|---|---|---|---|---|
HOPR | High Operating Range | FLOAT | Yes | 0 | Yes | Yes | No | No |
LOPR | Low Operating Range | FLOAT | Yes | 0 | Yes | Yes | No | No |
PREC | Display Precision | SHORT | Yes | 0 | Yes | Yes | No | No |
NAME | Record Name | STRING [29] | Yes | 0 | Yes | No | No | No |
DESC | Description | STRING [29] | Yes | Null | Yes | Yes | No | No |
Field | Summary | Type | DCT | Initial | Access | Modify | Rec Proc Monitor | PP |
---|---|---|---|---|---|---|---|---|
ADEL | Archive Deadband | DOUBLE | Yes | 0 | Yes | Yes | No | No |
MDEL | Monitor, i.e. value change, Deadband | DOUBLE | Yes | 0 | Yes | Yes | No | No |
The OVAL field is used to implement monitors on the VAL field. If VAL differs from OVAL (taking into account the deadband) then monitors for VAL are triggered.
The LA-LL fields are used to implement monitors for the A-L field, the fields which hold the values retrieved from the input links. They hold the values retrieved from INPA-INPL the last time the record was processed. For instance, when A, the current value retrieved from INPA, does not equal LA, the last value retrieved, then monitors for A are triggered.
The DOLV and CLCV are flag fields. The DOLV flag is used to indicate if the process variable specified in the Desired Output Location (DOLN) field is a valid name. If it is not, the desired output value is not retrieved from DOLN. The CLCV flag is used to indicate if the Wait record's CALC expression is a mathematically valid one.
The CBST field contains a pointer to a record private structure. It is not of concern to the user.
Field | Summary | Type | DCT | Initial | Access | Modify | Rec Proc Monitor | PP |
---|---|---|---|---|---|---|---|---|
CBST | Callback Structure | NOACCESS | No | Null | No | No | No | No |
OVAL | Old Value | DOUBLE | No | 0 | Yes | Yes | No | No |
DOLA | Desired Output Location Address | NOACCESS | No | Null | No | No | No | No |
DOLV | Desired Output Location Valid | LONG | No | 0 | Yes | Yes | Yes | No |
ALST | Archive Last Value | DOUBLE | No | 0 | Yes | No | No | No |
MLST | Monitor Last Value | DOUBLE | No | 0 | Yes | No | No | No |
CLCV | Calculation String Valid | LONG | No | 0 | Yes | Yes | Yes | No |
LA | Previous Input | DOUBLE | No | 0 | Yes | Yes | No | No |
LB | Previous Input | DOUBLE | No | 0 | Yes | Yes | No | No |
LC | Previous Input | DOUBLE | No | 0 | Yes | Yes | No | No |
LD | Previous Input | DOUBLE | No | 0 | Yes | Yes | No | No |
LE | Previous Input | DOUBLE | No | 0 | Yes | Yes | No | No |
LF | Previous Input | DOUBLE | No | 0 | Yes | Yes | No | No |
LG | Previous Input | DOUBLE | No | 0 | Yes | Yes | No | No |
LH | Previous Input | DOUBLE | No | 0 | Yes | Yes | No | No |
LI | Previous Input | DOUBLE | No | 0 | Yes | Yes | No | No |
LJ | Previous Input | DOUBLE | No | 0 | Yes | Yes | No | No |
LK | Previous Input | DOUBLE | No | 0 | Yes | Yes | No | No |
LL | Previous Input | DOUBLE | No | 0 | Yes | Yes | No | No |
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