RRM 3-14 Calculation

EPICS Record Reference Manual

Calc - Calculation

The calculation or "Calc" record is used to perform algebraic, relational, and logical operations on values retrieved from other records. The result of its operations can then be accessed by another record so that it can be used.

Parameter Fields

The fields in this record fall into these categories:

• scan parameters
• read parameters
• expression parameters
• operator display parameters
• alarm parameters
• monitor parameters
• run-time parameters

Scan Parameters

The Calc record has the standard fields for specifying under what circumstances the record will be processed. These fields are listed in Scan Fields. In addition, Scanning Specification explains how these fields are used. Since the Calc record supports no direct interfaces to hardware, it cannot be scanned on I/O interrupt, so its SCAN field cannot be I/O Intr.

Read Parameters

The read parameters for the Calc record consist of 12 input links INPA, INPB, ... INPL. The fields can be database links, channel access links, or constants. If they are links, they must specify another record's field or a channel access link. If they are constants, they will be initialized with the value they are configured with and can be changed via dbPuts. They cannot be hardware addresses.

See Address Specification for information on how to specify database links.

Field	Summary	Type	DCT	Initial	Access	Modify	Rec Proc Monitor
INPA	Input Link A	INLINK	Yes	0	No	No	N/A
INPB	Input Link B	INLINK	Yes	0	No	No	N/A
INPC	Input Link C	INLINK	Yes	0	No	No	N/A
INPD	Input Link D	INLINK	Yes	0	No	No	N/A
INPE	Input Link E	INLINK	Yes	0	No	No	N/A
INPF	Input Link F	INLINK	Yes	0	No	No	N/A
INPG	Input Link G	INLINK	Yes	0	No	No	N/A
INPH	Input Link H	INLINK	Yes	0	No	No	N/A
INPI	Input Link I	INLINK	Yes	0	No	No	N/A
INPJ	Input Link J	INLINK	Yes	0	No	No	N/A
INPK	Input Link K	INLINK	Yes	0	No	No	N/A
INPL	Input Link L	INLINK	Yes	0	No	No	N/A

Expression

At the core of the Calc record lie the CALC and RPCL fields. The CALC field contains the infix expression which the record routine will use when it processes the record. The resulting value is placed in the VAL field and can be accessed from there. The CALC expression is actually converted to opcode and stored as in Reverse Polish Notation in the RPCL field. It is this expression which is actually used to calculate VAL. The Reverse Polish expression is evaluated more efficiently during run-time than an infix expression. CALC can be changed at run-time, and a special record routine calls a function to convert it to Reverse Polish Notation.

The infix expressions that can be used are very similar to the C expression syntax, but with some additions and subtle differences in operator meaning and precedence. The string may contain a series of expressions separated by a semi-colon character ';' any one of which may actually provide the calculation result; however all of the other expressions included must assign their result to a variable. All alphabetic elements described below are case independent, so upper and lower case letters may be used and mixed in the variable and function names as desired. Spaces may be used anywhere within an expression except between the characters that make up a single expression element.

The range of expressions supported by the calculation record are separated into literals, constants, operands, algebraic operators, trigonometric operators, relational operators, logical operators, the assignment operator, parentheses and commas, and the question mark or '?:' operator.

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NOTE: A complete up-to-date description of the calculation expression can be found in the Application Developer's Guide, chapter libCom / calc / Infix Expression Syntax (19.2.1 for EPICS 3.14.11).

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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

Literals

• Standard double precision floating point numbers
• Inf: Infinity
• Nan: Not a Number

Constants

• PI: returns the mathematical constant π
• D2R: evaluates to π/180 which, when used as a multiplier, converts an angle from degrees to radians
• R2D: evaluates to 180/π which as a multiplier converts an angle from radians to degrees

Operands

The expression uses the values retrieved from the INPx links as operands, though constants can be used as operands too. These values retrieved from the input links are stored in the A-L fields. The values to be used in the expression are simply referenced by the field letter. For instance, the value obtained from the INPA link is stored in the field A, and the value obtained from INPB is stored in field B. The field names can be included in the expression which will operate on their respective values, as in A+B. Also, the RNDM unary function can be included as an operand in the expression in order to generate a random number between 0 and 1.

Field	Summary	Type	DCT	Initial	Access	Modify	Rec Proc Monitor	PP
A	Input Value A	DOUBLE	No	0	Yes	Yes/No	Yes	Yes
B	Input Value B	DOUBLE	No	0	Yes	Yes/No	Yes	Yes
C	Input Value C	DOUBLE	No	0	Yes	Yes/No	Yes	Yes
D	Input Value D	DOUBLE	No	0	Yes	Yes/No	Yes	Yes
E	Input Value E	DOUBLE	No	0	Yes	Yes/No	Yes	Yes
F	Input Value F	DOUBLE	No	0	Yes	Yes/No	Yes	Yes
G	Input Value G	DOUBLE	No	0	Yes	Yes/No	Yes	Yes
H	Input Value H	DOUBLE	No	0	Yes	Yes/No	Yes	Yes
I	Input Value I	DOUBLE	No	0	Yes	Yes/No	Yes	Yes
J	Input Value J	DOUBLE	No	0	Yes	Yes/No	Yes	Yes
K	Input Value K	DOUBLE	No	0	Yes	Yes/No	Yes	Yes
L	Input Value L	DOUBLE	No	0	Yes	Yes/No	Yes	Yes

The keyword VAL returns the current contents of the VAL field (which can be written to by a CA put, so it might not be the result from last time the expression was evaluated).

Also, the RNDM unary function can be included as an operand in the expression in order to generate a random number between 0 and 1.

Algebraic Operators

• ABS: Absolute value (unary)
• SQR: Square root (unary)
• MIN: Minimum (any number of args)
• MAX: Maximum (any number of args)
• FINITE: returns non-zero if none of the arguments are NaN or Inf (any number of args)
• ISNAN: returns non-zero if any of the arguments is NaN or Inf (any number of args)
• CEIL: Ceiling (unary)
• FLOOR: Floor (unary)
• LOG: Log base 10 (unary)
• LOGE: Natural log (unary)
• LN: Natural log (unary)
• EXP: Exponential function (unary)
• ^: Exponential (binary)
• ** : Exponential (binary)
• + : Addition (binary)
• - : Subtraction (binary)
• * : Multiplication (binary)
• / : Division (binary)
• % : Modulo (binary)
• NOT: Negate (unary)

Trigonometric Operators

• SIN: Sine
• SINH: Hyperbolic sine
• ASIN: Arc sine
• COS: Cosine
• COSH: Hyperbolic cosine
• ACOS: Arc cosine
• TAN: Tangent
• TANH: Hyperbolic tangent
• ATAN: Arc tangent

Relational Operators

• >= : Greater than or equal to
• > : Greater than
• <= : Less than or equal to
• <: Less than
• # : Not equal to
• = : Equal to

Logical Operators

• && : And
• || : Or
• ! : Not

Bitwise Operators

• | : Bitwise Or
• & : Bitwise And
• OR : Bitwise Or
• AND: Bitwise And
• XOR: Bitwise Exclusive Or
• ~ : One's Complement
• << : Left shift
• >> : Right shift

Assignment Operator

• := : assigns a value (right hand side) to a variable (i.e. field)

Parentheses, Comma, and Semicolon

The open and close parentheses are supported. Nested parenthesis are supported.

The comma is supported when used to separate the arguments of a binary function.

The semicolon is used to separate expressions. Although only one traditional calculation expression is allowed, multiple assignment expression area allowed.

Conditional Expression

The C language's question mark operator is supported. The format is:

condition ? True result : False result

Expression Examples

Algebraic

A + B + 10

• Result is A + B + 10

Relational

(A + B) < (C + D)

• Result is 1 if (A+B) < (C+D)
• Result is 0 if (A+B) >= (C+D)

Question Mark

(A+B)<(C+D)?E:F+L+10

• Result is E if (A+B) < (C+D)
• Result is F+L+10 if (A+B) >= (C+D)

(A+B)<(C+D)?E

• Result is E if (A+B) < (C+D)
• Result is unchanged if (A+B) >= (C+D)

Logical

A&B

• Causes the following to occur:
  • Convert A to integer
  • Convert B to integer
  • Bit-wise And A and B
  • Convert result to floating point

Operator Display Parameters

These parameters are used to present meaningful data to the operator. These fields are used to display VAL and the other parameters of the calculation record either textually or graphically.

The EGU field contains a string of up to 16 characters which is supplied by the user and which describes the values being operated upon. The string is retrieved whenever the routine get_units is called. The EGU string is solely for an operator's sake and does not have to be used.

The HOPR and LOPR fields only refer to the limits of the VAL, HIHI, HIGH, LOW, and LOLO fields. PREC controls the precision of the VAL field.

See 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
EGU	Engineering Units	STRING [16]	Yes	Null	Yes	Yes	No	No
PREC	Display Precision	SHORT	Yes	0	Yes	Yes	No	No
HOPR	High Operating Range	FLOAT	Yes	0	Yes	Yes	No	No
LOPR	Low Operating Range	FLOAT	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

Alarm Parameters

The possible alarm conditions for the Calc record are the SCAN, READ, Calculation, and limit alarms. The SCAN and READ alarms are called by the record support routines. The Calculation alarm is called by the record processing routine when the CALC expression is an invalid one, upon which an error message is generated.

The following alarm parameters which are configured by the user define the limit alarms for the VAL field and the severity corresponding to those conditions.

The HYST field defines an alarm deadband for each limit. See Alarm Specification for a complete explanation of alarms and these fields. Alarm Fields lists other fields related to alarms that are common to all record types.

Field	Summary	Type	DCT	Initial	Access	Modify	Rec Proc Monitor	PP
HIHI	Hihi Alarm Limit	FLOAT	Yes	0	Yes	Yes	No	Yes
HIGH	High Alarm Limit	FLOAT	Yes	0	Yes	Yes	No	Yes
LOW	Low Alarm Limit	FLOAT	Yes	0	Yes	Yes	No	Yes
LOLO	Lolo Alarm Limit	FLOAT	Yes	0	Yes	Yes	No	Yes
HHSV	Severity for a Hihi Alarm	GBLCHOICE	Yes	0	Yes	Yes	No	Yes
HSV	Severity for a High Alarm	GBLCHOICE	Yes	0	Yes	Yes	No	Yes
LSV	Severity for a Low Alarm	GBLCHOICE	Yes	0	Yes	Yes	No	Yes
LLSV	Severity for a Lolo Alarm	GBLCHOICE	Yes	0	Yes	Yes	No	Yes
HYST	Alarm Deadband	DOUBLE	Yes	0	Yes	Yes	No	No

Monitor Parameters

These parameters are used to determine when to send monitors for the value fields. The monitors are sent when the value field exceeds the last monitored field by the appropriate deadband, the ADEL for archiver monitors and the MDEL field for all other types of monitors. If these fields have a value of zero, everytime the value changes, monitors are triggered; if they have a value of -1, everytime the record is scanned, monitors are triggered. See Monitor Specification for a complete explanation of monitors.

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

Run-time Parameters

These fields are not configurable using a configuration too and none are modifiable at run-time. They are used to process the record.

The LALM field is used to implement the hysteresis factor for the alarm limits.

The LA-LL fields are used to decide when to trigger monitors for the corresponding fields. For instance, if LA does not equal the value for A, monitors for A are triggered. The MLST and MLST fields are used in the same manner for the VAL field.

Field	Summary	Type	DCT	Initial	Access	Modify	Rec Proc Monitor	PP
LALM	Last Alarmed Value	DOUBLE	No	0	Yes	No	No	No
ALST	Archive Last Value	DOUBLE	No	0	Yes	No	No	No
MLST	Monitor Last Value	DOUBLE	No	0	Yes	No	No	No
LA	Previous Input Value for A	DOUBLE	No	0	Yes	No	No	No
LB	Previous Input Value for A	DOUBLE	No	0	Yes	No	No	No
LC	Previous Input Value for A	DOUBLE	No	0	Yes	No	No	No
LD	Previous Input Value for A	DOUBLE	No	0	Yes	No	No	No
LE	Previous Input Value for A	DOUBLE	No	0	Yes	No	No	No
LF	Previous Input Value for A	DOUBLE	No	0	Yes	No	No	No
LG	Previous Input Value for A	DOUBLE	No	0	Yes	No	No	No
LH	Previous Input Value for A	DOUBLE	No	0	Yes	No	No	No
LI	Previous Input Value for A	DOUBLE	No	0	Yes	No	No	No
LJ	Previous Input Value for A	DOUBLE	No	0	Yes	No	No	No
LK	Previous Input Value for A	DOUBLE	No	0	Yes	No	No	No
LL	Previous Input Value for A	DOUBLE	No	0	Yes	No	No	No

Record Support

Record Support Routines

init_record

For each constant input link, the corresponding value field is initialized with the constant value if the input link is CONSTANT or a channel access link is created if the input link is PV_LINK.

A routine postfix is called to convert the infix expression in CALC to reverse polish notation. The result is stored in RPCL.

process

See next section.

special

This is called if CALC is changed. special calls postfix.

get_value

Fills in the values of struct valueDes so that they refer to VAL.

get_units

Retrieves EGU.

get_precision

Retrieves PREC.

get_graphic_double

Sets the upper display and lower display limits for a field. If the field is VAL, HIHI, HIGH, LOW, or LOLO, the limits are set to HOPR and LOPR, else if the field has upper and lower limits defined they will be used, else the upper and lower maximum values for the field type will be used.

get_control_double

Sets the upper control and the lower control limits for a field. If the field is VAL, HIHI, HIGH, LOW, or LOLO, the limits are set to HOPR and LOPR, else if the field has upper and lower limits defined they will be used, else the upper and lower maximum values for the field type will be used.

get_alarm_double

Sets the following values:

 upper_alarm_limit = HIHI
 upper_warning_limit = HIGH
 lower_warning_limit = LOW
 lower_alarm_limit = LOLO

Record Processing

Routine process implements the following algorithm:

1. Fetch all arguments.
2. Call routine calcPerform, which calculates VAL from the postfix version of the expression given in CALC. If calcPerform returns success UDF is set to FALSE.
3. Check alarms. This routine checks to see if the new VAL causes the alarm status and severity to change. If so, NSEV, NSTA and LALM are set. It also honors the alarm hysteresis factor (HYST). Thus the value must change by at least HYST before the alarm status and severity changes.
4. Check to see if monitors should be invoked.
   • Alarm monitors are invoked if the alarm status or severity has changed.
   • Archive and value change monitors are invoked if ADEL and MDEL conditions are met.
   • Monitors for A-L are checked whenever other monitors are invoked.
   • NSEV and NSTA are reset to 0.
5. Scan forward link if necessary, set PACT FALSE, and return.

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EPICS Record Reference Manual - 19 MAY 1998