This record type is normally used to send an analog value to an output device, converting it from engineering units into an integer value if necessary. The record supports alarm and drive limits, rate-of-change limiting, output value integration, linear and break-point conversion from engineering units, and graphics and control limits.
The OIF field which uses this menu controls whether the record acts as an integrator (
Incremental) or not (
Index Identifier Choice String 0 aoOIF_Full Full 1 aoOIF_Incremental Incremental
The record-specific fields are described below.
These fields control how the record determines the value to be output when it gets processed:
Field Summary Type DCT Default Read Write CA PP OMSL Output Mode Select MENU (menuOmsl) Yes Yes Yes No DOL Desired Output Loc INLINK Yes Yes Yes No OIF Out Full/Incremental MENU (aoOIF) Yes Yes Yes No PVAL Previous value DOUBLE No Yes No No DRVH Drive High Limit DOUBLE Yes Yes Yes Yes DRVL Drive Low Limit DOUBLE Yes Yes Yes Yes VAL Desired Output DOUBLE Yes Yes Yes Yes OROC Output Rate of Change DOUBLE Yes Yes Yes No OVAL Output Value DOUBLE No Yes Yes No
The following steps are performed in order during record processing.
The OMSL menu field is used to determine whether the DOL link and OIF menu fields should be used during processing or not:
If OMSL is
supervisory the DOL and OIF fields are not used. The new output value is taken from the VAL field, which may have been set from elsewhere.
If OMSL is
closed_loop the DOL link field is read to obtain a value; if OIF is
Incremental and the DOL link was read successfully, the record's previous output value PVAL is added to it.
The output value is now clipped to the range DRVL to DRVH inclusive, provided that DRVH > DRVL. The result is copied into both the VAL and PVAL fields.
If the OROC field is not zero, the VAL field is now adjusted so it is no more than OROC different to the previous output value given in OVAL. OROC thus determines the maximum change in the output value that can occur each time the record gets processed. The result is copied into the OVAL field, which is used as the input to the following Units Conversion processing stage.
For analog output records that do not use the Soft Channel device support routine, the specified conversions (if any) are performed on the OVAL field and the resulting value in the RVAL field is sent to the address contained in the output link after it is adjusted by the values in the AOFF and ASLO fields.
Field Summary Type DCT Default Read Write CA PP LINR Linearization MENU (menuConvert) Yes Yes Yes Yes RVAL Current Raw Value LONG No Yes Yes Yes ROFF Raw Offset ULONG No Yes Yes Yes EGUF Eng Units Full DOUBLE Yes Yes Yes Yes EGUL Eng Units Low DOUBLE Yes Yes Yes Yes AOFF Adjustment Offset DOUBLE Yes Yes Yes Yes ASLO Adjustment Slope DOUBLE Yes Yes Yes Yes ESLO EGU to Raw Slope DOUBLE Yes 1 Yes Yes Yes EOFF EGU to Raw Offset DOUBLE Yes Yes Yes Yes
Except for analog outputs that use Soft Channel device support, the LINR field determines if a conversion is performed and which conversion algorithm is used to convert OVAL to RVAL.
The LINR field can specify
SLOPE for linear conversions,
NO CONVERSION for no conversions at all, or the name of a breakpoint table such as
typeKdegC for breakpoint conversions.
The EGUF and EGUL fields should be set for
LINEAR conversions, and the ESLO and EOFF fields for
SLOPE conversion. Note that none of these fields have any significance for records that use the Soft Channel device support module.
The user must set these fields when configuring the database for records that use
LINEAR conversions. They are used to calculate the values for ESLO and EOFF. See Conversion Specification for more information on how to calculate these fields.
Computed by device support from EGUF and EGUL when LINR specifies
LINEAR. These values must be supplied by the user when LINR specifies
SLOPE. Used only when LINR is
These fields are adjustment parameters for the raw output values. They are applied to the raw output value after conversion from engineering units.
This field can be used to offset the raw value generated by the conversion process, which is needed for some kinds of hardware.
Conversion proceeds as follows:
To see how the Raw Soft Channel device support routine uses these fields, see "Device Support For Soft Records" below for more information.
The analog output record sends its desired output to the address in the OUT field. For analog outputs that write their values to devices, the OUT field must specify the address of the I/O card. In addition, the DTYP field must contain the name of the device support module. Be aware that the address format differs according to the I/O bus used. See Address Specification for information on the format of hardware addresses.
For soft records the output link can be a database link, a channel access link, or a constant value. If the link is a constant, no output is sent.
Field Summary Type DCT Default Read Write CA PP DTYP Device Type DEVICE Yes Yes Yes No OUT Output Specification OUTLINK Yes Yes Yes No
These parameters are used to present meaningful data to the operator. They display the value and other parameters of the analog output either textually or graphically.
EGU is a string of up to 16 characters describing the units that the analog output measures. It is retrieved by the get_units record support routine.
The HOPR and LOPR fields set the upper and lower display limits for the VAL, OVAL, PVAL, HIHI, HIGH, LOW, and LOLO fields. Both the get_graphic_double and get_control_double record support routines retrieve these fields. If these values are defined, they must be in the range: DRVL <= LOPR <= HOPR <= DRVH.
The PREC field determines the floating point precision with which to display VAL, OVAL and PVAL. It is used whenever the get_precision record support routine is called.
See Fields Common to All Record Types for more on the record name (NAME) and description (DESC) fields.
Field Summary Type DCT Default Read Write CA PP EGU Engineering Units STRING  Yes Yes Yes No HOPR High Operating Range DOUBLE Yes Yes Yes No LOPR Low Operating Range DOUBLE Yes Yes Yes No PREC Display Precision SHORT Yes Yes Yes No NAME Record Name STRING  No Yes No No DESC Descriptor STRING  Yes Yes Yes No
The possible alarm conditions for analog outputs are the SCAN, READ, INVALID and limit alarms. The SCAN, READ, and INVALID alarms are called by the record or device support routines.
The limit alarms are configured by the user in the HIHI, LOLO, HIGH, and LOW fields, which must be floating-point values. For each of these fields, there is a corresponding severity field which can be either NO_ALARM, MINOR, or MAJOR.
See Invalid Output Action Fields for more information on the IVOA and IVOV fields.
Alarm Fields lists other fields related to a alarms that are common to all record types.
Field Summary Type DCT Default Read Write CA PP HIHI Hihi Alarm Limit DOUBLE Yes Yes Yes Yes HIGH High Alarm Limit DOUBLE Yes Yes Yes Yes LOW Low Alarm Limit DOUBLE Yes Yes Yes Yes LOLO Lolo Alarm Limit DOUBLE Yes Yes Yes Yes HHSV Hihi Severity MENU (menuAlarmSevr) Yes Yes Yes Yes HSV High Severity MENU (menuAlarmSevr) Yes Yes Yes Yes LSV Low Severity MENU (menuAlarmSevr) Yes Yes Yes Yes LLSV Lolo Severity MENU (menuAlarmSevr) Yes Yes Yes Yes HYST Alarm Deadband DOUBLE Yes Yes Yes No IVOA INVALID output action MENU (menuIvoa) Yes Yes Yes No IVOV INVALID output value DOUBLE Yes Yes Yes No
These parameters are used to specify deadbands for monitors on the VAL field. The monitors are sent when the value field exceeds the last monitored field by the specified deadband. If these fields have a value of zero, everytime the value changes, a monitor will be triggered; if they have a value of -1, everytime the record is processed, monitors are triggered. ADEL is the deadband for archive monitors, and MDEL the deadband for all other types of monitors. See Monitor Specification for a complete explanation of monitors.
Field Summary Type DCT Default Read Write CA PP ADEL Archive Deadband DOUBLE Yes Yes Yes No MDEL Monitor Deadband DOUBLE Yes Yes Yes No
These parameters are used by the run-time code for processing the analog output. They are not configurable. They represent the current state of the record. The record support routines use some of them for more efficient processing.
The ORAW field is used to decide if monitors should be triggered for RVAL when monitors are triggered for VAL. The RBV field is the actual read back value obtained from the hardware itself or from the associated device driver. It is the responsibility of the device support routine to give this field a value.
ORBV is used to decide if monitors should be triggered for RBV at the same time monitors are triggered for changes in VAL.
The LALM, MLST, and ALST fields are used to implement the hysteresis factors for monitor callbacks.
The INIT field is used to initialize the LBRK field and for smoothing.
The PBRK field contains a pointer to the current breakpoint table (if any), and LBRK contains a pointer to the last breakpoint table used.
The OMOD field indicates whether OVAL differs from VAL. It will be different if VAL or OVAL have changed since the last time the record was processed, or if VAL has been adjusted by OROC during the current processing.
Field Summary Type DCT Default Read Write CA PP ORAW Previous Raw Value LONG No Yes No No RBV Readback Value LONG No Yes No No ORBV Prev Readback Value LONG No Yes No No LALM Last Value Alarmed DOUBLE No Yes No No ALST Last Value Archived DOUBLE No Yes No No MLST Last Val Monitored DOUBLE No Yes No No INIT Initialized? SHORT No Yes No No PBRK Ptrto brkTable NOACCESS No No No No LBRK LastBreak Point SHORT No Yes No No PVAL Previous value DOUBLE No Yes No No OMOD Was OVAL modified? UCHAR No Yes No No
The following fields are used when the record is in simulation mode. See Fields Common to Output Record Types for more information on these fields.
Field Summary Type DCT Default Read Write CA PP SIOL Sim Output Specifctn OUTLINK Yes Yes Yes No SIML Sim Mode Location INLINK Yes Yes Yes No SIMM Simulation Mode MENU (menuYesNo) No Yes Yes No SIMS Sim mode Alarm Svrty MENU (menuAlarmSevr) Yes Yes Yes No
The following are the record support routines that would be of interest to an application developer. Other routines are the get_units, get_precision, get_graphic_double, and get_control_double routines.
long init_record(aoRecord *prec, int pass);
This routine initializes SIMM if SIML is a constant or creates a channel access link if SIML is PV_LINK. If SIOL is PV_LINK a channel access link is created.
This routine next checks to see that device support is available. If DOL is a constant, then VAL is initialized with its value and UDF is set to FALSE.
The routine next checks to see if the device support write routine is defined. If either device support or the device support write routine does not exist, an error message is issued and processing is terminated.
For compatibility with old device supports that don't know EOFF, if both EOFF and ESLO have their default value, EOFF is set to EGUL.
If device support includes
init_record(), it is called.
INIT is set TRUE. This causes PBRK, LBRK, and smoothing to be re-initialized. If "backwards" linear conversion is requested, then VAL is computed from RVAL using the algorithm:
VAL = ((RVAL+ROFF) * ASLO + AOFF) * ESLO + EOFF
and UDF is set to FALSE.
For breakpoint conversion, a call is made to cvtEngToRawBpt and UDF is then set to FALSE. PVAL is set to VAL.
long process(aoRecord *prec);
See next section.
long special(DBADDR *paddr, int after);
The only special processing for analog output records is SPC_LINCONV which is invoked whenever either of the fields LINR, EGUF, EGUL or ROFF is changed If the device support routine special_linconv exists it is called.
INIT is set TRUE. This causes PBRK, LBRK, and smoothing to be re-initialized.
long get_alarm_double(DBADDR *, struct dbr_alDouble *);
Sets the following values:
upper_alarm_limit = HIHI upper_warning_limit = HIGH lower_warning_limit = LOW lower_alarm_limit = LOLO
Routine process implements the following algorithm:
if DOL is DB_LINK and OMSL is CLOSED_LOOP then get value from DOL
if OIF is INCREMENTAL then set value = value + VAL else value = VAL
If Drive limits are defined force value to be within limits
Set VAL equal to value
Set UDF to FALSE.
If OVAL is undefined set it equal to value
If OROC is defined and not 0 make |value-OVAL| <=OROC
Set OVAL equal to value
Compute RVAL from OVAL. using linear or break point table conversion. For linear conversions the algorithm is RVAL = (OVAL-EOFF)/ESLO.
For break point table conversion a call is made to cvtEngToRawBpt.
After that, for all conversion types AOFF, ASLO, and ROFF are calculated in, using the formula RVAL = (RVAL -AOFF) / ASLO - ROFF.
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 RVAL and for RBV are checked whenever other monitors are invoked.
NSEV and NSTA are reset to 0.
Each analog output record must have an associated set of device support routines. The primary responsibility of the device support routines is to output a new value whenever write_ao is called. The device support routines are primarily interested in the following fields:
PACT — Process Active, used to indicate asynchronous completion
DPVT — Device Private, reserved for device support to use
OUT — Output Link, provides addressing information
EGUF — Engineering Units Full
EGUL — Engineering Units Low
ESLO — Engineering Unit Slope
EOFF — Engineering Unit Offset
OVAL — Output Value, in Engineering units
RVAL — Raw Output Value, after conversion
Device support consists of the following routines:
long report(int level);
This optional routine is called by the IOC command
dbior and is passed the report level that was requested by the user. It should print a report on the state of the device support to stdout. The
level parameter may be used to output increasingly more detailed information at higher levels, or to select different types of information with different levels. Level zero should print no more than a small summary.
long init(int after);
This optional routine is called twice at IOC initialization time. The first call happens before any of the
init_record() calls are made, with the integer parameter
after set to 0. The second call happens after all of the
init_record() calls have been made, with
after set to 1.
long init_record(aoRecord *prec);
This optional routine is called by the record initialization code for each ao record instance that has its DTYP field set to use this device support. It is normally used to check that the OUT address has the expected type and points to a valid device; to allocate any record-specific buffer space and other memory; and to connect any communication channels needed for the
write_ao() routine to work properly.
If the record type's unit conversion features are used, the
init_record() routine should calculate appropriate values for the ESLO and EOFF fields from the EGUL and EGUF field values. This calculation only has to be performed if the record's LINR field is set to
LINEAR, but it is not necessary to check that condition first. This same calculation takes place in the
special_linconv() routine, so the implementation can usually just call that routine to perform the task.
If the the last output value can be read back from the hardware, this routine should also fetch that value and put it into the record's RVAL or VAL field. The return value should be zero if the RVAL field has been set, or 2 if either the VAL field has been set or if the last output value cannot be retrieved.
long get_ioint_info(int cmd, aoRecord *prec, IOSCANPVT *piosl);
This optional routine is called whenever the record's SCAN field is being changed to or from the value
I/O Intr to find out which I/O Interrupt Scan list the record should be added to or deleted from. If this routine is not provided, it will not be possible to set the SCAN field to the value
I/O Intr at all.
cmd parameter is zero when the record is being added to the scan list, and one when it is being removed from the list. The routine must determine which interrupt source the record should be connected to, which it indicates by the scan list that it points the location at
*piosl to before returning. It can prevent the SCAN field from being changed at all by returning a non-zero value to its caller.
In most cases the device support will create the I/O Interrupt Scan lists that it returns for itself, by calling
void scanIoInit(IOSCANPVT *piosl) once for each separate interrupt source. That API allocates memory and inializes the list, then passes back a pointer to the new list in the location at
*piosl. When the device support receives notification that the interrupt has occurred, it announces that to the IOC by calling
void scanIoRequest(IOSCANPVT iosl) which will arrange for the appropriate records to be processed in a suitable thread. The
scanIoRequest() routine is safe to call from an interrupt service routine on embedded architectures (vxWorks and RTEMS).
long write_ao(aoRecord *prec);
This essential routine is called whenever the record has a new output value to send to the device. It is responsible for performing the write operation, using either the engineering units value found in the record's OVAL field, or the raw value from the record's RVAL field if the record type's unit conversion facilities are used. A return value of zero indicates success, any other value indicates that an error occurred.
This routine must not block (busy-wait) if the device takes more than a few microseconds to accept the new value. In that case the routine must use asynchronous completion to tell the record when the write operation eventually completes. It signals that this is an asynchronous operation by setting the record's PACT field to TRUE before it returns, having arranged for the record's
process() routine to be called later once the write operation is over. When that happens the
write_ao() routine will be called again with PACT still set to TRUE; it should then set it to FALSE to indicate the write has completed, and return.
long special_linconv(aoRecord *prec, int after);
This optional routine should be provided if the record type's unit conversion features are used by the device support's
write_ao() routine utilizing the RVAL field rather than OVAL or VAL. It is called by the record code whenever any of the the fields LINR, EGUL or EGUF are modified and LINR has the value
LINEAR. The routine must calculate and set the fields EOFF and ESLO appropriately based on the new values of EGUL and EGUF.
These calculations can be expressed in terms of the minimum and maximum raw values that the
write_ao() routine can accept in the RVAL field. When VAL is EGUF the RVAL field will be set to RVAL_max, and when VAL is EGUL the RVAL field will become RVAL_min. The fomulae to use are:
EOFF = (RVAL_max * EGUL − RVAL_min * EGUF) / (RVAL_max − RVAL_min)
ESLO = (EGUF − EGUL) / (RVAL_max − RVAL_min)
Note that the record support sets EOFF to EGUL before calling this routine, which is a very common case (RVAL_min is zero).
Two soft device support modules Soft Channel and Raw Soft Channel are provided for output records not related to actual hardware devices. The OUT link type must be either a CONSTANT, DB_LINK, or CA_LINK.
This module writes the current value of OVAL.
If the OUT link type is PV_LINK, then dbCaAddInlink is called by
init_record() always returns a value of 2, which means that no conversion will ever be attempted.
write_ao calls recGblPutLinkValue to write the current value of VAL. See Soft Output for details.
This module is like the previous except that it writes the current value of RVAL.