RRM 3-14 Array Subroutine

aSub - Array Subroutine

The aSub record is a variant of the 'sub' (subroutine) record with array-valued input and output fields, whose types are user specifiable at database-configure time, and associated input and output links.

The routine to be called at process time can be changed dynamically after the database has been loaded. The name of the routine can either be fetched in over a link from another record or written directly into the SNAM field.

The user can configure the record to decide when events will be posted for the output fields. This can be: Never, Always or just when any element of an array changes value.

The VAL field holds the value returned from the routine called during record processing.

Field Summary

Field	Type	DCT	Initial	Access	Modify	Rec Proc Monitor	PP
VAL	LONG	No	0	Yes	Yes	Yes	No
OVAL	LONG	No	0	Yes	Yes	No	No
LFLG	MENU(IGNORE, READ)	Yes	IGNORE	Yes	Yes	No	No
EFLG	MENU(NEVER, ON CHANGE, ALWAYS)	Yes	ALWAYS	Yes	Yes	No	No
SUBL	INLINK	Yes	0	No	No	NA	No
INAM	STRING	Yes	Null	Yes	No	No	No
SNAM	STRING	Yes	Null	Yes	Yes	No	No
ONAM	STRING	Yes	Null	Yes	No	No	No
SADR	LONG	No	0	Yes	No	Yes	No
BRSV	MENU	Yes	0	Yes	Yes	No	Yes
PREC	SHORT	Yes	0	Yes	Yes	No	No
INPA	INLINK	Yes	0	No	No	NA	No
INPB	INLINK	Yes	0	No	No	NA	No
...	...	...	...	...	...	...	...
INPU	INLINK	Yes	0	No	No	NA	No
A	NOACCESS	No	0	No	Yes	No	No
B	NOACCESS	No	0	No	Yes	No	No
...	...	...	...	...	...	...	...
U	NOACCESS	No	0	No	Yes	No	No
FTA	MENU	Yes	DOUBLE	Yes	No	No	No
FTB	MENU	Yes	DOUBLE	Yes	No	No	No
...	...	...	...	...	...	...	...
FTU	MENU	Yes	DOUBLE	Yes	No	No	No
NOA	ULONG	Yes	1	Yes	No	No	No
NOB	ULONG	Yes	1	Yes	No	No	No
...	...	...	...	...	...	...	...
NOU	ULONG	Yes	1	Yes	No	No	No
NEA	ULONG	Yes	1	Yes	No	No	No
NEB	ULONG	Yes	1	Yes	No	No	No
...	...	...	...	...	...	...	...
NEU	ULONG	Yes	1	Yes	No	No	No
OUTA	OUTLINK	Yes	0	No	No	NA	No
OUTB	OUTLINK	Yes	0	No	No	NA	No
...	...	...	...	...	...	...	...
OUTU	OUTLINK	Yes	0	No	No	NA	No
VALA	NOACCESS	No	0	No	Yes	Yes	No
VALB	NOACCESS	No	0	No	Yes	Yes	No
...	...	...	...	...	...	...	...
VALU	NOACCESS	No	0	No	Yes	Yes	No
OVLA	NOACCESS	No	0	No	No	No	No
OVLB	NOACCESS	No	0	No	No	No	No
...	...	...	...	...	...	...	...
OVLU	NOACCESS	No	0	No	No	No	No
FTVA	MENU	Yes	DOUBLE	Yes	No	No	No
FTVB	MENU	Yes	DOUBLE	Yes	No	No	No
...	...	...	...	...	...	...	...
FTVU	MENU	Yes	DOUBLE	Yes	No	No	No
NOVA	ULONG	Yes	1	Yes	No	No	No
NOVB	ULONG	Yes	1	Yes	No	No	No
...	...	...	...	...	...	...	...
NOVU	ULONG	Yes	1	Yes	No	No	No
NEVA	ULONG	Yes	1	Yes	No	No	No
NEVB	ULONG	Yes	1	Yes	No	No	No
...	...	...	...	...	...	...	...
NEVU	ULONG	Yes	1	Yes	No	No	No

Field Descriptions

Name	Summary	Description
VAL	Value returned from process routine	This field holds the value returned from the user defined process routine.
OVAL	Old VAL	Previous VAL, used to decide when to post events.
LFLG	Link Flag	Tells the record whether to read or ignore the SUBL link. If the value is READ, then the name of the subroutine to be called at process time is read from SUBL. If the value is IGNORE, the name of the subroutine is that currently held in SNAM.
EFLG	Event Flag	Tells the record when to post change events on the output fields VALA,...,VALU. If the value is NEVER, events are never posted. If the value is ALWAYS, events are posted everytime the record processes. If the value is ON CHANGE, events are posted when any element of an array changes value. This flag controls value, log (archive) and alarm change events.
SUBL	Subroutine Link	Where to get the subroutine name from.
INAM	Initialisation Routine	This is the name of the initialisation routine to be called once, at iocInit.
SNAM	Process Routine	This is the name of the routine to be called when the record processes. Note, this can be overwritten by the SUBL link, if LFLG is set to READ.
ONAM	Process Routine	Old process subroutine name.
SADR	Subroutine Address	The address of the routine called at process time.
BRSV	Severity for a subroutine return value less than 0.	Specifies the Alarm severity.
PREC	Display Precision	Specifies the number of decimal places with which to display the values of the fields VALA,...,VALU.
INPA,..., INPU	Input Link A,..., Input Link U	The input links from where the values of A,...,U are fetched during record processing.
A,...,U	Input Fields	The input fields which hold the scalar values or arrays fetched in across the input links INPA,...,INPU.
FTA,..., FTU	Field Type of A Field Type of U	Field types of the input values. These can be any of the following: "STRING","CHAR","UCHAR","SHORT","USHORT","LONG","ULONG","FLOAT","DOUBLE, "ENUM".
NOA..., NOU	Max elements in A,.. Max elements in U	The number of elements of storage allocated for each input field. Default is 1 (scalar value). An array is specified by setting this field to greater than 1.
NEA..., NEU	Number of elements in A,.. Number of elements in U	The current number of elements stored in each input field. Field contains an array if this field is greater than 1.
OUTA,..., OUTU	Output Link A,.. Output Link U	The output links on which the scalars or arrays located at VALA,...,VALU are placed during record processing.
VALA,.., VALU	Output Fields	The output fields which hold the scalar values or arrays pushed out across the output links OUTA,...,OUTU.
FTVA,..., FTVU	Field Type of VALA Field Type of VALU	Field types of the output values. These can be CHAR, STRING, DOUBLE, LONG, etc.
OVLA,.., OVLU	Previous Outputs	The previous values of the outputs. These are used to decide when to post events if EFLG is set to ON CHANGE.
NOVA,..., NOVU	Max elements in VALA,.. Max elements in VALU	The number of elements of storage allocated for each output field. Default is 1 (scalar value). An array is specified by setting this field to greater than 1.
NEVA,..., NEVU	Number of elements in VALA,.. Number of elements in VALU	The current number of elements stored in each output field. Field contains an array if this field is greater than 1.

Record Support Routines

init_record

This routine is called twice at iocInit. On the first call it does the following:

• Calloc sufficient space to hold the number of input scalars and/or arrays defined by the settings of the fields FTA-FTU and NOA-NOU. Initialize fields NE* to the values of the associated NO* field values.
• Calloc sufficient space to hold the number of output scalars and/or arrays defined by the settings of the fields FTVA-FTVU and NOVA-NOVU. For the output fields, also calloc space to hold the previous value of a field. This is required when the decision is made on whether or not to post events.

On the second call, it does the following:

• Initializes SUBL if it is a constant link.
• Initializes each constant input link.
• If the field INAM is set, look-up the address of the routine and call it.
• If the field LFLG is set to IGNORE and SNAM is defined, look-up the address of the process routine.

process

This routine implements the following algorithm:

• If PACT is FALSE, perform normal processing
• If PACT is TRUE, perform asynchronous-completion processing

Normal processing:

• Set PACT to TRUE.
• If the field LFLG is set to READ, get the subroutine name from the SUBL link. If the name is not NULL and it is not the same as the previous subroutine name, lookup the subroutine address. Set the old subroutine name, ONAM, equal to the current name, SNAM.
• Fetch the values from the input links.
• Set PACT to FALSE
• If all input-link fetches succeeded, call the routine specified by SNAM.
• Set VAL equal to the return value from the routine specified by SNAM.
• If the SNAM routine set PACT to TRUE, then return. In this case, we presume the routine has arranged that process will be called at some later time for asynchronous completion.
• Set PACT to TRUE.
• Write the output values using the output links.
• Get the time of processing and put it into the timestamp field.
• If VAL has changed, post a change-of value and log event for this field. If EFLG is set to ALWAYS, post change-of-value and log events for every output field. If EFLG is set to ON CHANGE, post change-of-value and log events for every output field which has changed. In the case of an array, an event will be posted if any single element of the array has changed. If EFLG is set to NEVER, no change-of-value or log events are posted for the output fields.
• Process the record on the end of the forward link, if one exists.
• Set PACT to FALSE.

Asynchronous-completion processing:

• Call the routine specified by SNAM.
• Set VAL equal to the return value from the routine specified by SNAM.
• Set PACT to TRUE.
• Write the output values using the output links.
• Get the time of processing and put it into the timestamp field.
• If VAL has changed, post a change-of value and log event for this field. If EFLG is set to ALWAYS, post change-of-value and log events for every output field. If EFLG is set to ON CHANGE, post change-of-value and log events for every output field which has changed. In the case of an array, an event will be posted if any single element of the array has changed. If EFLG is set to NEVER, no change-of-value or log events are posted for the output fields.
• Process the record on the end of the forward link, if one exists.
• Set PACT to FALSE.

get_value

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

get_precision

Sets the display precision to the value of PREC for any of the output fields VALA,..., VALU. This routine could be called for any of these fields.

cvt_dbaddr

The purpose of this routine is to fill in the struct dbAddr for the field of the record for which it has been called. Typically, the number of elements in the field, the field type and the size of the field will be set in this routine. For arrays, this record support routine is essential.

get_array_info

This routine returns the current number of elements and the offset of the first value for an array. For this record, the offset field is always 0.

put_array_info

This routine is called after new values have been placed in an array.

special

This routine is called whenever the SNAM field changes. It is called twice, once before the change and once after. On the first call, the routine simply returns. On the second call, after SNAM has changed, it implements the following algorithm:

• If LFLG is set to IGNORE and SNAM is not NULL, then look-up the address of the routine specified by SNAM. Set the SADR field equal to the subroutine address.
• Post change-of-value and log events for the SADR field, if this has changed.

Use of the aSub Record

The aSub record has input-value fields (A-U) and output-value fields (VALA-VALU). There is no association between A and VALA, etc. The input-value fields have associated input links (INPA-INPU), and the output-value fields have associated output links (OUTA-OUTU). Both inputs and outputs have type fields (FTA-FTU, FTVA-FTVU, which default to 'DOUBLE') and number-of-element fields (NOA-NOU, NOVA-NOVU, which default to '1').

Example database fragment

To use the A field to read an array from some other record, then, you would need a database fragment that might look something like this:

   record(aSub,"my_asub_record") {
       field(SNAM,"my_asub_routine")
       ...
       field(FTA, "LONG")
       field(NOA, "100")
       field(INPA, "myWaveform_1 NPP NMS")
       ...
   }

If you wanted some other record to be able to write to the A field, then you would delete the input link above. If you wanted the A field to hold a scalar value, you would either delete the NOA specification, or specify it as "1".

Example subroutine fragment

The associated subroutine code that uses the A field might look like this:

   static long my_asub_routine(aSubRecord *prec) {
       long i, *a;
       double sum=0;
       ...
       a = (long *)prec->a;
       for (i=0; i<prec->noa; i++) {
           sum += a[i];
       }
       ...
       return(0)
   }

Note that the subroutine must always treat value fields (A-U, VALA-VALU) as arrays, even if they contain only a single element.

Required export code

Aside from your own code, you must include something like the following along with your subroutine code. This tells EPICS how to handle references to your subroutine:

   #include <registryFunction.h>
   #include <epicsExport.h>

   static registryFunctionRef my_asub_Ref[] = {
       {"my_asub_routine", (REGISTRYFUNCTION) my_asub_routine}
   };

   static void my_asub_Registrar(void) {
       registryFunctionRefAdd(my_asub_Ref, NELEMENTS(my_asub_Ref));
   }

   epicsExportRegistrar(my_asub_Registrar);

Required database-definition code

The .dbd file loaded into the ioc must contain something like the following, so EPICS can find the subroutine:

   registrar(my_asub_Registrar)

Device support, writing to hardware

Note, by the way, that the aSub record does not talk to device support. If you want to write to hardware, you might use your output fields and links to write to some other record that can write to hardware.

Dynamically Changing the User Routine called during Record Processing

The aSub record allows the user to dynamically change which routine is called when the record processes. This can be done in two ways:

• The LFLG field can be set to READ so that the name of the routine is read from the SUBL link. Thus, whatever is feeding this link can change the name of the routine before the aSub record is processed. In this case, the record looks in the symbol table for the symbol name whenever the name of routine fetched from the link changes.
• The LFLG field can be set to IGNORE. In this case, the routine called during record processing is that specified in the SNAM field. Under these conditions, the SNAM field can be changed by a Channel Access write to that field. Thus, during development work, when it is often required to run a modified version of the routine, it will no longer be a requirement to reboot the IOC and reload the database. A new routine will be called during record processing if the routine is loaded with the vxWorks ld command, and cau is used to put the name of the routine into the record's SNAM field. After the SNAM field has been changed, the record automatically looks up the symbol name in the symbol table. Note that, if the same routine name is used, this is not a problem. The record finds the latest version of the code which has been loaded. Obviously, one needs to take care of the amount of memory used in the system, if the vxWorks unld command is never used.