RRM 3-14 Compression - Revision history

RalphLange: HOPR, LOPR fields FLOAT -> DOUBLE

2012-12-03T12:29:29Z

HOPR, LOPR fields FLOAT -> DOUBLE

← Older revision		Revision as of 12:29, 3 December 2012
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	<TH>Field<TH>Summary<TH>Type<TH>DCT<TH>Initial<TH>Access<TH>Modify<TH>Rec Proc Monitor<TH>PP<TR>		<TH>Field<TH>Summary<TH>Type<TH>DCT<TH>Initial<TH>Access<TH>Modify<TH>Rec Proc Monitor<TH>PP<TR>
	<TD>EGU<TD>Engineering Units<TD>STRING [16]<TD>Yes<TD>null<TD>Yes<TD>Yes<TD>No<TD>No<TR>		<TD>EGU<TD>Engineering Units<TD>STRING [16]<TD>Yes<TD>null<TD>Yes<TD>Yes<TD>No<TD>No<TR>
	<TD>HOPR<TD>High Operating Range<TD>~~FLOAT~~<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>		<TD>HOPR<TD>High Operating Range<TD>DOUBLE<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>
	<TD>LOPR<TD>Low Operating Range<TD>~~FLOAT~~<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>		<TD>LOPR<TD>Low Operating Range<TD>DOUBLE<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>
	<TD>PREC<TD>Display Precision<TD>SHORT<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>		<TD>PREC<TD>Display Precision<TD>SHORT<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>
	<TD>NAME<TD>Record Name<TD>STRING [29]<TD>Yes<TD>0<TD>Yes<TD>No<TD>No<TD> <TR>		<TD>NAME<TD>Record Name<TD>STRING [29]<TD>Yes<TD>0<TD>Yes<TD>No<TD>No<TD> <TR>
	<TD>DESC<TD>Description<TD>STRING [29]<TD>Yes<TD>Null<TD>Yes<TD>Yes<TD>No<TD>No		<TD>DESC<TD>Description<TD>STRING [29]<TD>Yes<TD>Null<TD>Yes<TD>Yes<TD>No<TD>No
	</TABLE>		</TABLE>


	=== Alarm Parameters ===		=== Alarm Parameters ===

RalphLange: IHIL, ILIL fields FLOAT -> DOUBLE

2012-12-03T12:28:47Z

IHIL, ILIL fields FLOAT -> DOUBLE

← Older revision		Revision as of 12:28, 3 December 2012
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	<TD>NSAM<TD>Number in Sample<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>No<TD>No<TD>No<TR>		<TD>NSAM<TD>Number in Sample<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>No<TD>No<TD>No<TR>
	<TD>N<TD>Number<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>Yes<TD>No<TD>No<TR>		<TD>N<TD>Number<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>Yes<TD>No<TD>No<TR>
	<TD>ILIL<TD>Initial Low Interest Value<TD>~~FLOAT~~<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>		<TD>ILIL<TD>Initial Low Interest Value<TD>DOUBLE<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>
	<TD>IHIL<TD>Initial High Interest Value<TD>~~FLOAT~~<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No		<TD>IHIL<TD>Initial High Interest Value<TD>DOUBLE<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No
	</TABLE>		</TABLE>

AndrewJohnson: Added Median algorithm, reworded some other bits.

2011-06-07T19:59:21Z

Added Median algorithm, reworded some other bits.

← Older revision		Revision as of 19:59, 7 June 2011
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	=== Read Parameters and Algorithm Parameters ===		=== Read Parameters and Algorithm Parameters ===

	These fields determine what channel to read and how to compress the data. The user specifies the algorithm to be used in the ALG field. There are ~~five~~ possible algorithms which can be specified as follows:		These fields determine what channel to read and how to compress the data. The user specifies the algorithm to be used in the ALG field. There are six possible algorithms which can be specified as follows:

	* <CODE>Circular Buffer</CODE>		* <CODE>Circular Buffer</CODE>
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	* <CODE>N to 1 High Value</CODE>		* <CODE>N to 1 High Value</CODE>
	* <CODE>N to 1 Average</CODE>		* <CODE>N to 1 Average</CODE>
			* <CODE>N to 1 Median</CODE>

	These algorithms are explained in one of the sections below.		These algorithms are explained in one of the sections below.
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	[[Image:RRM 3-14 Compression-1.gif]]		[[Image:RRM 3-14 Compression-1.gif]]

	If <CODE>N to 1 ~~Low Value</CODE>, <CODE>N to 1 High Value</CODE>, or <CODE>N to 1 Average~~</CODE> are chosen, then VAL is a circular buffer of NSAM samples. The actual algorithm depends on whether INP references a scalar or an array. If INP refers to a scalar, then N successive time ordered samples of INP are taken. After the Nth sample is obtained a new value, determined by the algorithm (~~LOW~~, ~~HIGH~~, or ~~AVE~~), is written to the circular buffer referenced by VAL. If ~~LOW,~~ the lowest value is written; if ~~HIGH,~~ the highest value ~~of all the samples~~ is written; and if ~~AVE~~, the average of all the samples are written.		If any of the <CODE>N to 1</CODE>algorithms are chosen, then VAL is a circular buffer of NSAM samples.

			The actual algorithm depends on whether INP references a scalar or an array. If INP refers to a scalar, then N successive time ordered samples of INP are taken. After the Nth sample is obtained a new value, determined by the algorithm (Lowest, Highest, or Average), is written to the circular buffer referenced by VAL. If <CODE>Low Value</CODE> the lowest value of all the samples is written; if <CODE>High Value</CODE> the highest value is written; and if <CODE>Average</CODE>, the average of all the samples are written. The <CODE>Median</CODE> setting behaves like <CODE>Average</CODE> with scalar input data.

	If INP refers to an array, then the following applies:		If INP refers to an array, then the following applies:

	; <CODE>N to 1 Low Value</CODE>		; <CODE>N to 1 Low Value</CODE>
	: Compress N to 1 samples, keeping the lowest value		: Compress N to 1 samples, keeping the lowest value.
	; <CODE>N to 1 High Value</CODE>		; <CODE>N to 1 High Value</CODE>
	: Compress N to 1 samples, keeping the highest value		: Compress N to 1 samples, keeping the highest value.
	; <CODE>N to 1 Average</CODE>		; <CODE>N to 1 Average</CODE>
	: Compress N to 1 samples, taking the average		: Compress N to 1 samples, taking the average value.
			; <CODE>N to 1 Median</CODE>
			: Compress N to 1 samples, taking the median value.

	The compression record keeps (NSAM) data samples.		The compression record keeps NSAM data samples.

	The N ~~field~~ determines the number of ~~fields~~ to compress into 1.		The field N determines the number of elements to compress into each result.

	Thus, if NSAM was 3, and N was also equal to 3, then the algorithms would work as in the following diagram:		Thus, if NSAM was 3, and N was also equal to 3, then the algorithms would work as in the following diagram:
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	[[Image:RRM 3-14 Compression-2.gif]]		[[Image:RRM 3-14 Compression-2.gif]]

	~~OFF number of samples are ignored at the beginning of the array being compressed.~~ IHIL and ILIL ~~are used as~~ initial value ~~filters when compressing arrays~~; ~~that is, the compression does not begin~~ until a value is found that is ~~either greater than~~ IHIL ~~or less than ILIL~~		IHIL and ILIL can be set to provide an initial value filter on the input array. If ILIL < IHIL input elements will be skipped until a value is found that is in the range ILIL to IHIL.

	RES resets the algorithm before the maximum number of samples are reached.		RES resets the algorithm before the maximum number of samples are reached.

RalphLange: /* Algorithms and Related Fields */ Fix description of Average algorithm

2010-09-30T16:32:56Z

Algorithms and Related Fields: Fix description of Average algorithm

← Older revision		Revision as of 16:32, 30 September 2010
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	The <CODE>Circular Buffer</CODE> algorithm keeps a circular buffer of length NSAM. Each time the record is processed, it gets the data referenced by INP and puts it into the circular buffer referenced by VAL. Note that when INP refers to a scalar, VAL is just a time ordered circular buffer of values obtained from INP.		The <CODE>Circular Buffer</CODE> algorithm keeps a circular buffer of length NSAM. Each time the record is processed, it gets the data referenced by INP and puts it into the circular buffer referenced by VAL. Note that when INP refers to a scalar, VAL is just a time ordered circular buffer of values obtained from INP.

	<CODE>Average</CODE> takes an average of ~~all the elements~~ of the array obtained from INP; that is, the entire array referenced by INP is retrieved, and the average ~~of the elements~~ is placed in the ~~next~~ element of the ~~circular~~ buffer. The retrieved array is truncated to be of length NSAM. N successive arrays are averaged and placed in the ~~circular~~ buffer. Thus, VAL[0] holds the average of the first ~~sampling~~ of INP, VAL[1] holds the average of the next ~~sampling~~ of INP, and so on. The following shows the equation:		<CODE>Average</CODE> takes an average of every element of the array obtained from INP over time; that is, the entire array referenced by INP is retrieved, and for each element the new average is calculated and placed in the corresponding element of the value buffer. The retrieved array is truncated to be of length NSAM. N successive arrays are averaged and placed in the buffer. Thus, VAL[0] holds the average of the first element of INP over N samples, VAL[1] holds the average of the next element of INP over N samples, and so on. The following shows the equation:

	[[Image:RRM 3-14 Compression-1.gif]]		[[Image:RRM 3-14 Compression-1.gif]]

RalphLange: /* Read Parameters and Algorithm Parameters */ Fix: ALG and N are SPC_RESET, not SPC_NOMOD.

2010-04-08T15:08:06Z

Read Parameters and Algorithm Parameters: Fix: ALG and N are SPC_RESET, not SPC_NOMOD.

← Older revision		Revision as of 15:08, 8 April 2010
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	<TH>Field<TH>Summary<TH>Type<TH>DCT<TH>Initial<TH>Access<TH>Modify<TH>Rec Proc Monitor<TH>PP<TR>		<TH>Field<TH>Summary<TH>Type<TH>DCT<TH>Initial<TH>Access<TH>Modify<TH>Rec Proc Monitor<TH>PP<TR>
	<TD>RES<TD>Reset<TD>SHORT<TD>No<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>		<TD>RES<TD>Reset<TD>SHORT<TD>No<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>
	<TD>ALG<TD>Algorithm<TD>[[RRM 3-14 Menu Choices\|RECCHOICE]]<TD>Yes<TD>0<TD>Yes<TD>No<TD>No<TD>No<TR>		<TD>ALG<TD>Algorithm<TD>[[RRM 3-14 Menu Choices\|RECCHOICE]]<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>
	<TD>NSAM<TD>Number in Sample<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>No<TD>No<TD>No<TR>		<TD>NSAM<TD>Number in Sample<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>No<TD>No<TD>No<TR>
	<TD>N<TD>Number<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>No<TD>No<TD>No<TR>		<TD>N<TD>Number<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>Yes<TD>No<TD>No<TR>
	<TD>ILIL<TD>Initial Low Interest Value<TD>FLOAT<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>		<TD>ILIL<TD>Initial Low Interest Value<TD>FLOAT<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>
	<TD>IHIL<TD>Initial High Interest Value<TD>FLOAT<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No		<TD>IHIL<TD>Initial High Interest Value<TD>FLOAT<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No
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	RES resets the algorithm before the maximum number of samples are reached.		RES resets the algorithm before the maximum number of samples are reached.


	=== Operator Display Parameters ===		=== Operator Display Parameters ===

RalphLange: /* special */ Fix: ALG and N are SPC_RESET, not SPC_NOMOD.

2010-04-08T15:05:20Z

special: Fix: ALG and N are SPC_RESET, not SPC_NOMOD.

← Older revision		Revision as of 15:05, 8 April 2010
Line 156:		Line 156:
	==== special ====		==== special ====

	This routine is called when RSET is set. It performs a reset.		This routine is called when RSET, ALG, or N are set. It performs a reset.

	==== get_value ====		==== get_value ====

KazimierzGofron at 19:11, 18 April 2008

2008-04-18T19:11:05Z

← Older revision		Revision as of 19:11, 18 April 2008
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	=== Scanning Parameters ===		=== Scanning Parameters ===

	The compression record has the standard fields for specifying under what circumstances the record will be processed. These fields are listed in [[RRM 3-13 dbCommon#Scan Fields\|Scan Fields]]. In addition, [[RRM 3-13 Concepts#Scanning Specification\|Scanning Specification]] explains how these fields are used. Since the compression record supports no direct interfaces to hardware, its SCAN field cannot specify <CODE>I/O Intr</CODE>.		The compression record has the standard fields for specifying under what circumstances the record will be processed. These fields are listed in [[RRM 3-14 dbCommon#Scan Fields\|Scan Fields]]. In addition, [[RRM 3-14 Concepts#Scanning Specification\|Scanning Specification]] explains how these fields are used. Since the compression record supports no direct interfaces to hardware, its SCAN field cannot specify <CODE>I/O Intr</CODE>.


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	<TH>Field<TH>Summary<TH>Type<TH>DCT<TH>Initial<TH>Access<TH>Modify<TH>Rec Proc Monitor<TH>PP<TR>		<TH>Field<TH>Summary<TH>Type<TH>DCT<TH>Initial<TH>Access<TH>Modify<TH>Rec Proc Monitor<TH>PP<TR>
	<TD>RES<TD>Reset<TD>SHORT<TD>No<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>		<TD>RES<TD>Reset<TD>SHORT<TD>No<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>
	<TD>ALG<TD>Algorithm<TD>[[RRM 3-13 Menu Choices\|RECCHOICE]]<TD>Yes<TD>0<TD>Yes<TD>No<TD>No<TD>No<TR>		<TD>ALG<TD>Algorithm<TD>[[RRM 3-14 Menu Choices\|RECCHOICE]]<TD>Yes<TD>0<TD>Yes<TD>No<TD>No<TD>No<TR>
	<TD>NSAM<TD>Number in Sample<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>No<TD>No<TD>No<TR>		<TD>NSAM<TD>Number in Sample<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>No<TD>No<TD>No<TR>
	<TD>N<TD>Number<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>No<TD>No<TD>No<TR>		<TD>N<TD>Number<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>No<TD>No<TD>No<TR>
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	==== Input Specification ====		==== Input Specification ====

	The input specification should be a database or channel access link. Though INP can be a constant, the data compression algorithms are supported only when INP is a database link. See [[RRM 3-13 Concepts#Address Specification\|Address Specification]] for information on specifying links.		The input specification should be a database or channel access link. Though INP can be a constant, the data compression algorithms are supported only when INP is a database link. See [[RRM 3-14 Concepts#Address Specification\|Address Specification]] for information on specifying links.


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	<CODE>Average</CODE> takes an average of all the elements of the array obtained from INP; that is, the entire array referenced by INP is retrieved, and the average of the elements is placed in the next element of the circular buffer. The retrieved array is truncated to be of length NSAM. N successive arrays are averaged and placed in the circular buffer. Thus, VAL[0] holds the average of the first sampling of INP, VAL[1] holds the average of the next sampling of INP, and so on. The following shows the equation:		<CODE>Average</CODE> takes an average of all the elements of the array obtained from INP; that is, the entire array referenced by INP is retrieved, and the average of the elements is placed in the next element of the circular buffer. The retrieved array is truncated to be of length NSAM. N successive arrays are averaged and placed in the circular buffer. Thus, VAL[0] holds the average of the first sampling of INP, VAL[1] holds the average of the next sampling of INP, and so on. The following shows the equation:

	[[Image:RRM 3-13 Compression-1.gif]]		[[Image:RRM 3-14 Compression-1.gif]]

	If <CODE>N to 1 Low Value</CODE>, <CODE>N to 1 High Value</CODE>, or <CODE>N to 1 Average</CODE> are chosen, then VAL is a circular buffer of NSAM samples. The actual algorithm depends on whether INP references a scalar or an array. If INP refers to a scalar, then N successive time ordered samples of INP are taken. After the Nth sample is obtained a new value, determined by the algorithm (LOW, HIGH, or AVE), is written to the circular buffer referenced by VAL. If LOW, the lowest value is written; if HIGH, the highest value of all the samples is written; and if AVE, the average of all the samples are written.		If <CODE>N to 1 Low Value</CODE>, <CODE>N to 1 High Value</CODE>, or <CODE>N to 1 Average</CODE> are chosen, then VAL is a circular buffer of NSAM samples. The actual algorithm depends on whether INP references a scalar or an array. If INP refers to a scalar, then N successive time ordered samples of INP are taken. After the Nth sample is obtained a new value, determined by the algorithm (LOW, HIGH, or AVE), is written to the circular buffer referenced by VAL. If LOW, the lowest value is written; if HIGH, the highest value of all the samples is written; and if AVE, the average of all the samples are written.
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	Thus, if NSAM was 3, and N was also equal to 3, then the algorithms would work as in the following diagram:		Thus, if NSAM was 3, and N was also equal to 3, then the algorithms would work as in the following diagram:

	[[Image:RRM 3-13 Compression-2.gif]]		[[Image:RRM 3-14 Compression-2.gif]]

	OFF number of samples are ignored at the beginning of the array being compressed. IHIL and ILIL are used as initial value filters when compressing arrays; that is, the compression does not begin until a value is found that is either greater than IHIL or less than ILIL		OFF number of samples are ignored at the beginning of the array being compressed. IHIL and ILIL are used as initial value filters when compressing arrays; that is, the compression does not begin until a value is found that is either greater than IHIL or less than ILIL
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	The EGU field should be given a string that describes the value of VAL, but is used whenever the <CODE>get_units</CODE> record support routine is called.		The EGU field should be given a string that describes the value of VAL, but is used whenever the <CODE>get_units</CODE> record support routine is called.

	See [[RRM 3-13 dbCommon#Fields Common to All Record Types\|Fields Common to All Record Types]] for more on the record name (NAME) and description (DESC) fields.		See [[RRM 3-14 dbCommon#Fields Common to All Record Types\|Fields Common to All Record Types]] for more on the record name (NAME) and description (DESC) fields.


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	=== Alarm Parameters ===		=== Alarm Parameters ===

	The compression record has the alarm parameters common to all record types. [[RRM 3-13 dbCommon#Alarm Fields\|Alarm Fields]] lists other fields related to a alarms that are common to all record types.		The compression record has the alarm parameters common to all record types. [[RRM 3-14 dbCommon#Alarm Fields\|Alarm Fields]] lists other fields related to a alarms that are common to all record types.

KazimierzGofron at 18:28, 18 April 2008

2008-04-18T18:28:50Z

New page

[[RRM 3-14|EPICS Record Reference Manual]]

= compress - Compression =

The data compression record is used to collect and compress data from arrays. When the INP field references a data array field, it immediately compresses the entire array into an element of an array using one of several algorithms, overwriting the previous element. If the INP field obtains its value from a scalar-value field, the compression record will collect a new sample each time the record is processed and add it to the compressed data array as a circular buffer.

The INP link can also specify a constant; however, if this is the case, the compression algorithms are ignored, and the record support routines merely return after checking the FLNK field.

== Parameter Fields ==

The data compression fields fall into the following categories:

* scan parameters
* read parameters
* operator display parameters
* run-time parameters

=== Scanning Parameters ===

The compression record has the standard fields for specifying under what circumstances the record will be processed. These fields are listed in [[RRM 3-13 dbCommon#Scan Fields|Scan Fields]]. In addition, [[RRM 3-13 Concepts#Scanning Specification|Scanning Specification]] explains how these fields are used. Since the compression record supports no direct interfaces to hardware, its SCAN field cannot specify <CODE>I/O Intr</CODE>.

=== Read Parameters and Algorithm Parameters ===

These fields determine what channel to read and how to compress the data. The user specifies the algorithm to be used in the ALG field. There are five possible algorithms which can be specified as follows:

* <CODE>Circular Buffer</CODE>
* <CODE>Average</CODE>
* <CODE>N to 1 Low Value</CODE>
* <CODE>N to 1 High Value</CODE>
* <CODE>N to 1 Average</CODE>

These algorithms are explained in one of the sections below.

The RES field can be accessed at run time to cause the algorithm to reset itself.

<TABLE BORDER="1">
<TH>Field<TH>Summary<TH>Type<TH>DCT<TH>Initial<TH>Access<TH>Modify<TH>Rec Proc Monitor<TH>PP<TR>
<TD>RES<TD>Reset<TD>SHORT<TD>No<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>
<TD>ALG<TD>Algorithm<TD>[[RRM 3-13 Menu Choices|RECCHOICE]]<TD>Yes<TD>0<TD>Yes<TD>No<TD>No<TD>No<TR>
<TD>NSAM<TD>Number in Sample<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>No<TD>No<TD>No<TR>
<TD>N<TD>Number<TD>ULONG<TD>Yes<TD>1<TD>Yes<TD>No<TD>No<TD>No<TR>
<TD>ILIL<TD>Initial Low Interest Value<TD>FLOAT<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>
<TD>IHIL<TD>Initial High Interest Value<TD>FLOAT<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No
</TABLE>

==== Input Specification ====

The input specification should be a database or channel access link. Though INP can be a constant, the data compression algorithms are supported only when INP is a database link. See [[RRM 3-13 Concepts#Address Specification|Address Specification]] for information on specifying links.

==== Algorithms and Related Fields ====

As stated above, the ALG field specifies which algorithm to be performed on the data. The rest of the fields--NSAM, N, ILIL, IHIL, and OFF--are used in the compressions, though N is not used in the <CODE>Circular Buffer</CODE> algorithm and ILIL, IHIL, and OFF are used neither in the <CODE>Circular Buffer</CODE> algorithm nor in the <CODE>Average</CODE> algorithm.

The <CODE>Circular Buffer</CODE> algorithm keeps a circular buffer of length NSAM. Each time the record is processed, it gets the data referenced by INP and puts it into the circular buffer referenced by VAL. Note that when INP refers to a scalar, VAL is just a time ordered circular buffer of values obtained from INP.

<CODE>Average</CODE> takes an average of all the elements of the array obtained from INP; that is, the entire array referenced by INP is retrieved, and the average of the elements is placed in the next element of the circular buffer. The retrieved array is truncated to be of length NSAM. N successive arrays are averaged and placed in the circular buffer. Thus, VAL[0] holds the average of the first sampling of INP, VAL[1] holds the average of the next sampling of INP, and so on. The following shows the equation:

[[Image:RRM 3-13 Compression-1.gif]]

If <CODE>N to 1 Low Value</CODE>, <CODE>N to 1 High Value</CODE>, or <CODE>N to 1 Average</CODE> are chosen, then VAL is a circular buffer of NSAM samples. The actual algorithm depends on whether INP references a scalar or an array. If INP refers to a scalar, then N successive time ordered samples of INP are taken. After the Nth sample is obtained a new value, determined by the algorithm (LOW, HIGH, or AVE), is written to the circular buffer referenced by VAL. If LOW, the lowest value is written; if HIGH, the highest value of all the samples is written; and if AVE, the average of all the samples are written.

If INP refers to an array, then the following applies:

; <CODE>N to 1 Low Value</CODE>
: Compress N to 1 samples, keeping the lowest value
; <CODE>N to 1 High Value</CODE>
: Compress N to 1 samples, keeping the highest value
; <CODE>N to 1 Average</CODE>
: Compress N to 1 samples, taking the average

The compression record keeps (NSAM) data samples.

The N field determines the number of fields to compress into 1.

Thus, if NSAM was 3, and N was also equal to 3, then the algorithms would work as in the following diagram:

[[Image:RRM 3-13 Compression-2.gif]]

OFF number of samples are ignored at the beginning of the array being compressed. IHIL and ILIL are used as initial value filters when compressing arrays; that is, the compression does not begin until a value is found that is either greater than IHIL or less than ILIL

RES resets the algorithm before the maximum number of samples are reached.

=== Operator Display Parameters ===

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

The HOPR and LOPR fields only specify the range for VAL, HIHI, HIGH, LOLO and LOW fields.

PREC controls the floating-point precision whenever <CODE>get_precision</CODE> is called, and the field being referenced is the VAL field (i.e., one of the values contained in the circular buffer).

The EGU field should be given a string that describes the value of VAL, but is used whenever the <CODE>get_units</CODE> record support routine is called.

See [[RRM 3-13 dbCommon#Fields Common to All Record Types|Fields Common to All Record Types]] for more on the record name (NAME) and description (DESC) fields.

<TABLE BORDER="1">
<TH>Field<TH>Summary<TH>Type<TH>DCT<TH>Initial<TH>Access<TH>Modify<TH>Rec Proc Monitor<TH>PP<TR>
<TD>EGU<TD>Engineering Units<TD>STRING [16]<TD>Yes<TD>null<TD>Yes<TD>Yes<TD>No<TD>No<TR>
<TD>HOPR<TD>High Operating Range<TD>FLOAT<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>
<TD>LOPR<TD>Low Operating Range<TD>FLOAT<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>
<TD>PREC<TD>Display Precision<TD>SHORT<TD>Yes<TD>0<TD>Yes<TD>Yes<TD>No<TD>No<TR>
<TD>NAME<TD>Record Name<TD>STRING [29]<TD>Yes<TD>0<TD>Yes<TD>No<TD>No<TD> <TR>
<TD>DESC<TD>Description<TD>STRING [29]<TD>Yes<TD>Null<TD>Yes<TD>Yes<TD>No<TD>No
</TABLE>

=== Alarm Parameters ===

The compression record has the alarm parameters common to all record types. [[RRM 3-13 dbCommon#Alarm Fields|Alarm Fields]] lists other fields related to a alarms that are common to all record types.

=== Run-time Parameters ===

These parameters are used by the run-time code for processing the data compression algorithm. They are not configurable by the user, though some are accessible at run-time. They can represent the current state of the waveform or of the record whose field is referenced by the INP field.

NUSE holds the number of elements currently stored in VAL.

BPTR is a pointer that refers to the buffer referenced by VAL.

The SPTR field pointer to an array that is used for array averages.

WPTR is used by the dbGetlinks routines.

<TABLE BORDER="1">
<TH>Field<TH>Summary<TH>Type<TH>DCT<TH>Initial<TH>Access<TH>Modify<TH>Rec Proc Monitor<TH>PP<TR>
<TD>NUSE<TD>Number Used<TD>ULONG<TD>No<TD>0<TD>Yes<TD>No<TD>No<TD>No<TR>
<TD>BPTR<TD>Buffer Pointer<TD>NOACCESS<TD>No<TD>0<TD>No<TD>No<TD>No<TD> <TR>
<TD>SPTR<TD>Summing Buffer Pointer<TD>NOACCESS<TD>No<TD>0<TD>No<TD>No<TD>No<TD> <TR>
<TD>WPTR<TD>Work Buffer Pointer<TD>NOACCESS<TD>No<TD>0<TD>No<TD>No<TD>No<TD> <TR>
<TD>CVB<TD>Compress Value Buffer<TD>DOUBLE<TD>No<TD>0<TD>Yes<TD>No<TD>No<TD>No<TR>
<TD>INX<TD>Current Index of Circular Buffer<TD>ULONG<TD>No<TD>0<TD>Yes<TD>No<TD>No<TD>No
</TABLE>

== Record Support ==

=== Record Support Routines ===

==== init_record ====

Space for all necessary arrays is allocated. The addresses are stored in the appropriate fields in the record.

==== process ====

See next section.

==== special ====

This routine is called when RSET is set. It performs a reset.

==== get_value ====

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

==== cvt_dbaddr ====

This is called by dbNameToAddr. It makes the dbAddr structure refer to the actual buffer holding the result.

==== get_array_info ====

Obtains values from the circular buffer referenced by VAL.

==== put_array_info ====

Writes values into the circular buffer referenced by 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, 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, 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.

=== Record Processing ===

Routine process implements the following algorithm:

# If INP is not a database link, check monitors and the forward link and return.
# Get the current data referenced by INP.
# Perform the appropriate algorithm:
#* Average: Read N successive instances of INP and perform an element by element average. Until N instances have been obtained it just return without checking monitors or the forward link. When N instances have been obtained complete the algorithm, store the result in the VAL array, check monitors and the forward link, and return.
#* Circular Buffer: Write the values obtained from INP into the VAL array as a circular buffer, check monitors and the forward link, and return.
#* N to 1 xxx and INP refers to a scalar: Obtain N successive values from INP and apply the NTO1xxx algorithm to these values. Until N values are obtained monitors and forward links are not checked. When N successive values have been obtained, complete the algorithm, check monitors and the forward link, and return.
#* N to 1 xxx and INP refers to an array: The ILIL and IHIL are honored if ILIL < IHIL. The input array is divided into subarrays of length N. The specified N to 1 xxx compression algorithm is applied to each sub-array and the result stored in the array referenced by VAL. The monitors and forward link are checked.
# If success, set UDF to FALSE.
# Check to see if monitors should be invoked:
#* Alarm monitors are invoked if the alarm status or severity has changed.
#* NSEV and NSTA are reset to 0.
# Scan forward link if necessary, set PACT FALSE, and return.

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EPICS Record Reference Manual - 19 MAY 1998