Array Subroutine Record (aSub)

The aSub record is an advanced variant of the ‘sub’ (subroutine) record which has a number of additional features:

It provides 21 different input and output fields which can hold array or scalar values. The types and array capacities of these are user configurable, and they all have an associated input or output link.
The name of the C or C++ subroutine to be called when the record processes can be changed dynamically while the IOC is running. The name can either be fetched from another record using an input link, or written directly into the SNAM field.
The user can choose whether monitor events should be posted for the output fields.
The VAL field is set to the return value from the user subroutine, which is treated as a status value and controls whether the output links will be used or not. The record can also raise an alarm with a chosen severity if the status value is non-zero.

This record type was included in base.dbd beginning with epics-base 3.14.10 .

Record-specific Menus

Menu aSubLFLG

The LFLG menu field controls whether the SUBL link will be read to update the name of the subroutine to be called when the record processes.

Index	Identifier	Choice String
0	aSubLFLG_IGNORE	IGNORE
1	aSubLFLG_READ	READ

Menu aSubEFLG

The EFLG menu field indicates whether monitor events should be posted for the VALA…VALU output value fields.

Index	Identifier	Choice String
0	aSubEFLG_NEVER	NEVER
1	aSubEFLG_ON_CHANGE	ON CHANGE
2	aSubEFLG_ALWAYS	ALWAYS

Parameter Fields

The record-specific fields are described below.

Subroutine Fields

The VAL field is set to the value returned by the user subroutine. The value is treated as an error status value where zero mean success. The output links OUTA … OUTU will only be used to forward the associated output value fields when the subroutine has returned a zero status. If the return status was less than zero, the record will be put into SOFT_ALARM state with severity given by the BRSV field.

The INAM field may be used to name a subroutine that will be called once at IOC initialization time.

LFLG 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.

A string is read from the SUBL link to fetch the name of the subroutine to be run during record processing.

SNAM holds the name of the subroutine to be called when the record processes. The value in this field can be overwritten by the SUBL link if LFLG is set to READ.

The SADR field is only accessible from C code; it points to the subroutine to be called.

The CADR field may be set by the user subroutine to point to another function that will be called immediately before setting the SADR field to some other routine. This allows the main user subroutine to allocate resources when it is first called and be able to release them again when they are no longer needed.

Field	Summary	Type	DCT	Read	Write	CA PP
VAL	Subr. return value	LONG	No	Yes	Yes	No
OVAL	Old return value	LONG	No	Yes	No	No
INAM	Initialize Subr. Name	STRING [41]	Yes	Yes	No	No
LFLG	Subr. Input Enable	MENU aSubLFLG	Yes	Yes	Yes	No
SUBL	Subroutine Name Link	INLINK	Yes	Yes	No	No
SNAM	Process Subr. Name	STRING [41]	Yes	Yes	Yes	No
ONAM	Old Subr. Name	STRING [41]	Yes	Yes	No	No
SADR	Subroutine Address	NOACCESS	No	No	No	No
CADR	Subroutine Cleanup Address	NOACCESS	No	No	No	No
BRSV	Bad Return Severity	MENU menuAlarmSevr	Yes	Yes	Yes	Yes

Operator Display Parameters

The PREC field specifies the number of decimal places with which to display the values of the value fields A … U and VALA … VALU. Except when it doesn’t.

Output Event Flag

This field 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 every time 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.

Field	Summary	Type	DCT	Default	Read	Write	CA PP
EFLG	Output Event Flag	MENU aSubEFLG	Yes	1	Yes	Yes	No

Input Link Fields

The input links from where the values of A,…,U are fetched during record processing.

Field	Summary	Type	DCT	Read	Write	CA PP
INPA	Input Link A	INLINK	Yes	Yes	Yes	No
⋮
INPU	Input Link U	INLINK	Yes	Yes	Yes	No

Input Value Fields

These fields hold the scalar or array values fetched through the input links INPA,…,INPU.

Field	Summary	Type	DCT	Read	Write	CA PP
A	Input value A	Set by FTA[NOA]	No	Yes	Yes	No
⋮
U	Input value U	Set by FTU[NOU]	No	Yes	Yes	No

Input Value Data Types

Field types of the input value fields. The choices can be found by following the link to the menuFtype definition.

Field	Summary	Type	DCT	Default	Read	Write	CA PP
FTA	Type of A	MENU menuFtype	Yes	DOUBLE	Yes	No	No
⋮
FTU	Type of U	MENU menuFtype	Yes	DOUBLE	Yes	No	No

Input Value Array Capacity

These fields specify how many array elements the input value fields may hold.

Note that access to the NOT field from C code must use the field name in upper case, e.g. prec->NOT since the lower-case not is a reserved word in C++ and cannot be used as an identifier.

Field	Summary	Type	DCT	Default	Read	Write	CA PP
NOA	Max. elements in A	ULONG	Yes	1	Yes	No	No
⋮
NOU	Max. elements in U	ULONG	Yes	1	Yes	No	No

Input Value Array Size

These fields specify how many array elements the input value fields currently contain.

Field	Summary	Type	DCT	Default	Read	Write	CA PP
NEA	Num. elements in A	ULONG	No	1	Yes	No	No
⋮
NEU	Num. elements in U	ULONG	No	1	Yes	No	No

Output Link Fields

The output links through which the VALA … VALU field values are sent during record processing, provided the subroutine returned 0.

Field	Summary	Type	DCT	Read	Write	CA PP
OUTA	Output Link A	OUTLINK	Yes	Yes	Yes	No
⋮
OUTU	Output Link U	OUTLINK	Yes	Yes	Yes	No

Output Value Fields

These fields hold scalar or array data generated by the subroutine which will be sent through the OUTA … OUTU links during record processing.

Field	Summary	Type	DCT	Read	Write	CA PP
VALA	Output value A	Set by FTVA[NOVA]	No	Yes	Yes	No
⋮
VALU	Output value U	Set by FTVU[NOVU]	No	Yes	Yes	No

Old Value Fields

The previous values of the output fields. These are used to determine when to post events if EFLG is set to ON CHANGE.

Field	Summary	Type	DCT	Read	Write	CA PP
OVLA	Old Output A	NOACCESS	No	No	No	No
⋮
OVLU	Old Output U	NOACCESS	No	No	No	No

Output Value Data Types

Field types of the output value fields. The choices can be found by following a link to the menuFtype definition.

Field	Summary	Type	DCT	Default	Read	Write	CA PP
FTVA	Type of VALA	MENU menuFtype	Yes	DOUBLE	Yes	No	No
⋮
FTVU	Type of VALU	MENU menuFtype	Yes	DOUBLE	Yes	No	No

Output Value Array Capacity

These fields specify how many array elements the output value fields may hold.

Field	Summary	Type	DCT	Default	Read	Write	CA PP
NOVA	Max. elements in VALA	ULONG	Yes	1	Yes	No	No
⋮
NOVU	Max. elements in VALU	ULONG	Yes	1	Yes	No	No

Output Value Array Size

These fields specify how many array elements the output value fields currently contain.

Field	Summary	Type	DCT	Default	Read	Write	CA PP
NEVA	Num. elements in VALA	ULONG	No	1	Yes	No	No
⋮
NEVU	Num. elements in VALU	ULONG	No	1	Yes	No	No

Old Value Array Size

These fields specify how many array elements the old value fields currently contain.

Field	Summary	Type	DCT	Default	Read	Write	CA PP
ONVA	Num. elements in OVLA	ULONG	No	1	Yes	No	No
⋮
ONVU	Num. elements in OVLU	ULONG	No	1	Yes	No	No

Record Support Routines

init_record

long (*init_record)(struct dbCommon *precord, int pass)

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

long (*process)(struct dbCommon *precord)

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, look up 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.
If VAL is zero, 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 (again).
Set VAL equal to the return value from the routine specified by SNAM.
Set PACT to TRUE.
If VAL is zero, 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.

Use of the aSub Record

The aSub record has input-value fields (A-U) and output-value fields (VALA-VALU), which are completely independent. 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’). The output links OUTA-OUTU will only be processed if the subroutine returns a zero (OK) status value.

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;
    epicsInt32 *a;

    double sum=0;
    ...
    a = (epicsInt32 *)prec->a;
    for (i=0; i<prec->noa; i++) {
        sum += a[i];
    }
    ...
    return 0; /* process output links */
}

Note that the subroutine code must always handle the 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 export and register your subroutines so the record can locate them. The simplest way is as follows:

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

static long my_asub_routine(aSubRecord *prec) {
    ...
}
epicsRegisterFunction(my_asub_routine);

Required database-definition code

The .dbd file loaded by the ioc must then contain the following line, which tells the linker to include your object file in the IOC binary:

function(my_asub_routine)

Device support, writing to hardware

The aSub record does not call any device support routines. 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. During development when trying several versions of the routine, it is not necessary to reboot the IOC and reload the database. A new routine can be loaded with the vxWorks ld command, and Channel Access or the dbpf command used to put the name of the routine into the record’s SNAM field. The record will look up the symbol name in the symbol table whenever the SNAM field gets modified. The same routine name can even be used as the vxWorks symbol lookup returns the latest version of the code to have been loaded.