The Sequence record is used to trigger the processing of up to ten other records and send values to those records. It is similar to the fanout record, except that it will fetch an input value and write an output value instead of simply processing a collection of forward links. It can also specify one of several selection algorithms that determine which values to write. It has no associated device support.
The record-specific fields are described below, grouped by functionality.
The sequence record has the standard fields for specifying under what circumstances it will be processed. These fields are listed in Scan Fields.
These fields determine where the record retrieves the values it is to write to other records. All of these values are not necessarily used, depending on the selection algorithm.
The sequence record can retrieve up to 16 values from 16 locations. The user specifies the locations in the Desired Output Link fields (DOL0-DOLF), which can be either constants, database links, or channel access links. If a Desired Output Link is a constant, the corresponding value field for that link is initialized to the constant value. Otherwise, if the Desired Output Link is a database or channel access link, a value is fetched from the link each time the record is processed.
The value fetched from the Desired Output Links are stored in the corresponding Desired Output Value fields (DO0-DOF). These fields can be initialized to a constant value, and may subsequently be changed via dbPuts.
Field Summary Type DCT Default Read Write CA PP DOL0 Input link 0 INLINK Yes Yes Yes No DOL1 Input link1 INLINK Yes Yes Yes No DOL2 Input link 2 INLINK Yes Yes Yes No DOL3 Input link 3 INLINK Yes Yes Yes No DOL4 Input link 4 INLINK Yes Yes Yes No DOL5 Input link 5 INLINK Yes Yes Yes No DOL6 Input link 6 INLINK Yes Yes Yes No DOL7 Input link 7 INLINK Yes Yes Yes No DOL8 Input link 8 INLINK Yes Yes Yes No DOL9 Input link 9 INLINK Yes Yes Yes No DOLA Input link 10 INLINK Yes Yes Yes No DOLB Input link 11 INLINK Yes Yes Yes No DOLC Input link 12 INLINK Yes Yes Yes No DOLD Input link 13 INLINK Yes Yes Yes No DOLE Input link 14 INLINK Yes Yes Yes No DOLF Input link 15 INLINK Yes Yes Yes No
Field Summary Type DCT Default Read Write CA PP DO0 Value 0 DOUBLE No Yes Yes No DO1 Value 1 DOUBLE No Yes Yes No DO2 Value 2 DOUBLE No Yes Yes No DO3 Value 3 DOUBLE No Yes Yes No DO4 Value 4 DOUBLE No Yes Yes No DO5 Value 5 DOUBLE No Yes Yes No DO6 Value 6 DOUBLE No Yes Yes No DO7 Value 7 DOUBLE No Yes Yes No DO8 Value 8 DOUBLE No Yes Yes No DO9 Value 9 DOUBLE No Yes Yes No DOA Value 10 DOUBLE No Yes Yes No DOB Value 11 DOUBLE No Yes Yes No DOC Value 12 DOUBLE No Yes Yes No DOD Value 13 DOUBLE No Yes Yes No DOE Value 14 DOUBLE No Yes Yes No DOF Value 15 DOUBLE No Yes Yes No
When the record is processed, the desired output values are retrieved for the links in the record's selection algorithm and are written to the corresponding output link (LNK0-LNKF). These output links can be database links or channel access links; they cannot be device addresses. There are sixteen output links, one for each desired output link. Only those that are defined are used.
Field Summary Type DCT Default Read Write CA PP LNK0 Output Link 0 OUTLINK Yes Yes Yes No LNK1 Output Link 1 OUTLINK Yes Yes Yes No LNK2 Output Link 2 OUTLINK Yes Yes Yes No LNK3 Output Link 3 OUTLINK Yes Yes Yes No LNK4 Output Link 4 OUTLINK Yes Yes Yes No LNK5 Output Link 5 OUTLINK Yes Yes Yes No LNK6 Output Link 6 OUTLINK Yes Yes Yes No LNK7 Output Link 7 OUTLINK Yes Yes Yes No LNK8 Output Link 8 OUTLINK Yes Yes Yes No LNK9 Output Link 9 OUTLINK Yes Yes Yes No LNKA Output Link 10 OUTLINK Yes Yes Yes No LNKB Output Link 11 OUTLINK Yes Yes Yes No LNKC Output Link 12 OUTLINK Yes Yes Yes No LNKD Output Link 13 OUTLINK Yes Yes Yes No LNKE Output Link 14 OUTLINK Yes Yes Yes No LNKF Output Link 15 OUTLINK Yes Yes Yes No
When the sequence record is processed,
it uses a selection algorithm similar to that of the selection record to decide which links to process.The select mechanism field (SELM) has three algorithms to choose from: All,
<<Specified >> or Mask.
Field Summary Type DCT Default Read Write CA PP SELM Select Mechanism MENU (seqSELM) Yes Yes Yes No SELN Link Selection USHORT No 1 Yes Yes No SELL Link Selection Loc INLINK Yes Yes Yes No SHFT Shift for Mask mode SHORT Yes -1 Yes Yes No OFFS Offset for Specified SHORT Yes Yes Yes No
SELM - Selection Mode
Index Identifier Choice String 0 seqSELM_All All 1 seqSELM_Specified Specified 2 seqSELM_Mask Mask
See "Selection Algorithms Description" below;
SELL - Link Selection Location
This field can be initialized as a CONSTANT or as a LINK to any other record.
SELN will fetch its value from this field when the seq record is processed.
Thus,
when using Mask or Specified modes,
the links that seq will process can be dynamically changed by the record pointed by SELL.
SELN - Link Selection
When SELM = Specified this is the index number of the link that will be processed,
used in combination with the OFFS field:
SELN = SELN + OFFS
(By default, the OFFS is initalized to ZERO)
When SELM = Mask this field is the bitmask that will be used to determine which links will be processed by the seq record, in combination with the SHFT field:
if (SHFT >= 0)
SELN = SELN << -SHFT
else
SELN = SELN >> SHFT
(By default, the SHFT is initalized to -1)
The first versions of seq record had DO, DOL, LNK and DLY fields starting with index ONE (DO1, DOL1, LNK1 and DLY1). Since EPICS 7 the seq record now supports 16 links, starting from index ZERO (DO0, DOL0, LNK0 and DLY0). The SHFT and OFFS fields were introduced to keep compatibility of old databases that used seq records with links indexed from one.
To use the DO0, DOL0, LNK0, DLY0 fields when SELM = Mask, the SHFT field must be set to ZERO
All
The All algorithm causes the record to process each input and output link each time the record is processed, in order from 0 to 15. So when SELM is All, the desired output value from DOL0 will fetched and sent to LNK0, then the desired output value from DOL1 will be fetched and sent to the location in LNK1, and so on until the last input and output link DOF and LNKF. (Note that undefined links are not used.) If DOLx is a constant, the current value field is simply used and the desired output link is ignored. The SELN field is not used when All is the algorithm.
Specified
When the Specified algorithm is chosen, each time the record is processed it gets the integer value in the Link Selection (SELN) field and uses that as the index of the link to process. For instance, if SELN is 4, the desired output value from DO4 will be retrieved and sent to LNK4. If DOLx is a constant, DOx is simply used without the value being fetched from the input link.
Mask
When Mask is chosen, the record uses the individual bits of the SELN field to determine the links to process. When bit 0 of SELN is set, the value from DO0 will be written to the location in LNK0; when bit 1 is set, the valud from DO1 will be written to the location in LNK1 etc. Thus for example if SELN is 3, the record will retrieve the values from DO0 and DO1 and write them to the locations in LNK0 and LNK1, respectively. If SELN is 63, DO0...DO5 will be written to LNK0...LNK5.
The delay parameters consist of 16 fields, one for each I/O link discussed above. These fields can be configured to cause the record to delay processing the link. For instance, if the user gives the DLY1 field a value of 3.0, each time the record is processed at run-time, the record will delay processing the DOL1, DOV1, and LNK1 fields for three seconds. That is, the desired output value will not be fetched and written to the output link until three seconds have lapsed.
Field Summary Type DCT Default Read Write CA PP DLY0 Delay 0 DOUBLE Yes Yes Yes No DLY1 Delay 1 DOUBLE Yes Yes Yes No DLY2 Delay 2 DOUBLE Yes Yes Yes No DLY3 Delay 3 DOUBLE Yes Yes Yes No DLY4 Delay 4 DOUBLE Yes Yes Yes No DLY5 Delay 5 DOUBLE Yes Yes Yes No DLY6 Delay 6 DOUBLE Yes Yes Yes No DLY7 Delay 7 DOUBLE Yes Yes Yes No DLY8 Delay 8 DOUBLE Yes Yes Yes No DLY9 Delay 9 DOUBLE Yes Yes Yes No DLYA Delay 10 DOUBLE Yes Yes Yes No DLYB Delay 11 DOUBLE Yes Yes Yes No DLYC Delay 12 DOUBLE Yes Yes Yes No DLYD Delay 13 DOUBLE Yes Yes Yes No DLYE Delay 14 DOUBLE Yes Yes Yes No DLYF Delay 15 DOUBLE Yes Yes Yes No
These parameters are used to present meaningful data to the operator. The Precision field (PREC) determines the decimal precision for the VAL field when it is displayed. It is used when the get_precision record 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 PREC Display Precision SHORT Yes Yes Yes No NAME Record Name STRING [61] No Yes No No DESC Descriptor STRING [41] Yes Yes Yes No
The sequence record has the alarm parameters common to all record types. Alarm Fields lists the fields related to alarms that are common to all record types.
Routine process implements the following algorithm:
For the delay mechanism to operate properly, the record is processed asynchronously. The only time the record will not be processed asynchronously is when there are no non-NULL output links selected (i.e. when it has nothing to do.) The processing of the links is done via callback tasks at the priority set in the PRIO field in dbCommon (see the Application Developer's Guide for more information on call