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Add introduction of PCD database in PCD PEIM.
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@7973 6f19259b-4bc3-4df7-8a09-765794883524
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@ -893,7 +893,7 @@ typedef struct {
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space guid: token number} to local token number.
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@param Guid Token space guid for dynamic-ex PCD entry.
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@param ExTokenNumber EDES_TODO: Add parameter description
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@param ExTokenNumber Token number for dynamic-ex PCD.
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@return local token number for dynamic-ex PCD.
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@ -1011,3 +1011,251 @@ SetPtrTypeSize (
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extern PEI_PCD_DATABASE_INIT gPEIPcdDbInit;
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#endif
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////////////////////////////////////////////////////////////////////////////////
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// //
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// Introduction of PEI PCD database //
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// //
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////////////////////////////////////////////////////////////////////////////////
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/**
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1, Introduction
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PEI PCD database hold all dynamic type PCD information used in PEI phase.
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The structure of PEI PCD database is generated by build tools according to
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dynamic PCD usage for specified platform.
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2, Dynamic Type PCD
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Dynamic type PCD is designed for accessing setting which value is determined
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dynamic. In contrast, the value of static type PCD (FeatureFlag, FixedPcd,
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PatchablePcd) is fixed in final generated FD image in build time.
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2.1 The "dynamic" determination means:
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a) The PCD value is produced by someone driver and consumed by other driver
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in execution time.
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b) The PCD value is set/get by user from FrontPage.
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c) The PCD value is produced by platform OEM specified area.
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2.2 According to distribution mehod, dynamic PCD could be classfied as:
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a) Dynamic:
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This type PCD is used for module in source distribution which will be
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built in platform.
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b) DynamicEx:
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This type PCD is used for module in binary distribution which will be
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will not built.
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2.3 According to storage method, dynamic PCD could be classfied as:
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a) Default Storage:
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- The value is stored in PCD database maintained by PCD database in boot
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time memory which is built as a guid hob in PEI phase.
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- This type is used for communication between PEIM/DXE driver, DXE/DXE
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driver. But all set/get value will be losted after boot-time memory
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is turn off.
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- [PcdsDynamicDefault]/[PcdsDynamicExDefault] is used as section name
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for this type PCD in platform DSC file.
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b) Variable Storage:
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- The value is stored in variable area.
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- As default storage type, this type PCD could used for communication.
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But beside it, this type PCD could be used store the value associating
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with HII setting via variable technology.
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- In PEI phase, the PCD value could only be got but can not be set due
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to variable area is readonly for PEI phase.
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- [PcdsDynamicHii]/[PcdsDynamicExHii] is used as section name for this
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type PCD in platform DSC file.
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c) OEM specificed storage area:
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- The value is stored in OEM specified area, the base address is specified
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by a FixedAtBuild PCD PcdVpdBaseAddress.
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- The area is read only for PEI and DXE phase.
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- [PcdsDynamicVpd]/[PcdsDynamicExVpd] is used as section name for this
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type PCD in platform DSC file.
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Note: The default value of dynamic PCD are storaged in memory maintained
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by PEI/DXE PCD drvier.
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2.4 When and how to use dynamic PCD
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Module developer do not care the used PCD is dynamic or static when writting
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source code/INF. Dynamic PCD and dynamic type is pointed by platform integrator
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in platform DSC file. Please ref section 2.3 to get matching between dynamic
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PCD type and section name in DSC file.
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3, PCD database:
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Although dynamic PCD could be in different storage type as above description,
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but the basic information and default value for all dynamic PCD is hold
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by PCD database maintained by PEI/DXE driver.
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As whole EFI BIOS boot path is divided into PEI/DXE phase, the PCD database
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also is divided into Pei/Dxe database maintaied by PcdPeim/PcdDxe driver separatly.
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To make PcdPeim's driver image smaller, PEI PCD database only hold all dynamic
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PCD information used in PEI phase or use in both PEI/DXE phase. And DXE PCD
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database contains all PCDs used in PEI/DXE phase in memory.
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Build tool will generate PCD database into some C structure and variable for
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PEI/DXE PCD driver according to dynamic PCD section in platform DSC file.
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3.1 PcdPeim and PcdDxe
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PEI PCD database is maintained by PcdPeim driver run from flash. PcdPeim driver
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build guid hob in temporary memory and copy auto-generated C structure
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to temporary memory for PEI PCD database.
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DXE PCD database is maintained by PcdDxe driver.At entry point of PcdDxe driver,
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a new PCD database is allocated in boot-time memory which including all
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PEI PCD and DXE PCD entry.
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Pcd driver should run as early as possible before any other driver access
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dynamic PCD's value. PEI/DXE "Apriori File" mechanism make it possible by
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making PcdPeim/PcdDxe as first dispatching driver in PEI/DXE phase.
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3.2 Token space Guid/Token number, Platform token, Local token number
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Dynamic PCD
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+-----------+ +---------+
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|TokenSpace | |Platform |
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| Guid | build tool | Token |
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| + +-------------->| Number |
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| Token | +---------+`._
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| Number | `.
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+-----------+ `. +------+
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`-|Local |
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|Token |
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DynamicEx PCD ,-|Number|
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+-----------+ ,-' +------+
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|TokenSpace | ,-'
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| Guid | _,-'
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| + +.'
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| Token |
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| Number |
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+-----------+
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3.2.1 Pair of Token space guid + Token number
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Any type PCD is identified by pair of "TokenSpaceGuid + TokeNumber". But it
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is not easy maintained by PCD driver, and hashed token number will make
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searching slowly.
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3.2.2 Platform Token Number
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"Platform token number" concept is introduced for mapping to a pair of
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"TokenSpaceGuid + TokenNumber". The platform token number is generated by
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build tool in autogen.h and all of them are continual in a platform scope
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started from 1.(0 meaning invalid internal token number)
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With auto-generated "platform token number", PcdGet(PcdSampleDynamicPcd)
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in source code is translated to LibPcdGet(_PCD_TOKEN_PcdSampleDynamicPcd)
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in autogen.h.
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Notes: The mapping between pair of "tokenspace guid + token number" and
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"internal token number" need build tool establish, so "platform token number"
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mechanism is not suitable for binary module which use DynamicEx type PCD.
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To access a dynamicEx type PCD, pair of "token space guid/token number" all need
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to be specificed for PcdSet/PcdGet accessing macro.
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3.2.3 Local Token Number
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To fast searching a PCD entry in PCD database, PCD driver translate
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platform token number to local token number via a mapping table.
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For binary DynamicEx type PCD, there is a another mapping table to translate
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"token space guid + token number" to local token number directly.
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Local token number is identifier for all internal interface in PCD PEI/DXE
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driver.
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A local token number is a 32-bit value in following meaning:
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32 ------------- 28 ---------- 24 -------- 0
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| PCD type mask | Datum Type | Offset |
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+-----------------------------------------+
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where:
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PCd type mask: indicate Pcd type from following macro:
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PCD_TYPE_DATA
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PCD_TYPE_HII
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PCD_TYPE_VPD
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PCD_TYPE_SKU_ENABLED
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PCD_TYPE_STRING
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Datum Type : indicate PCD vaue type from following macro:
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PCD_DATUM_TYPE_POINTER
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PCD_DATUM_TYPE_UINT8
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PCD_DATUM_TYPE_UINT16
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PCD_DATUM_TYPE_UINT32
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PCD_DATUM_TYPE_UINT64
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Offset : indicate the related offset of PCD value in PCD database array.
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Based on local token number, PCD driver could fast determine PCD type, value
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type and get PCD entry from PCD database.
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3.3 PCD Database C structure.
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PCD Database C structure is generated by build tools in PCD driver's autogen.h/
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autogen.c file. In generated C structure, following information is stored:
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- ExMapTable: This table is used translate a binary dynamicex type PCD's
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"tokenguid + token" to local token number.
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- LocalTokenNumberTable:
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This table stores all local token number in array, use "Internal
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token number" as array index to get PCD entry's offset fastly.
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- SizeTable: This table stores the size information for all PCD entry.
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- GuidTable: This table stores guid value for DynamicEx's token space,
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HII type PCD's variable.
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- SkuIdTable: TBD
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- SystemSkuId: TBD
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- PCD value structure:
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Every PCD has a value record in PCD database. For different
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datum type PCD has different record structure which will be
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introduced in 3.3.1
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In a PCD database structure, there are two major area: Init and UnInit.
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Init area is use stored above PCD internal structure such as ExMapTable,
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LocalTokenNumberTable etc and the (default) value of PCD which has default
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value specified in platform DSC file.
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Unint area is used stored the value of PCD which has no default value in
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platform DSC file, the value of NULL, 0 specified in platform DSC file can
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be seemed as "no default value".
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3.3.1 Simple Sample PCD Database C Structure
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A general sample of PCD database structue is as follows:
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typedef struct _PCD_DATABASE {
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typedef struct _PCD_DATABASE_INIT {
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//===== Following is PCD database internal maintain structures
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DYNAMICEX_MAPPING ExMapTable[PEI_EXMAPPING_TABLE_SIZE];
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UINT32 LocalTokenNumberTable[PEI_LOCAL_TOKEN_NUMBER_TABLE_SIZE];
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GUID GuidTable[PEI_GUID_TABLE_SIZE];
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SIZE_INFO SizeTable[PEI_SIZE_TABLE_SIZE];
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UINT8 SkuIdTable[PEI_SKUID_TABLE_SIZE];
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SKU_ID SystemSkuId;
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//===== Following is value structure for PCD with default value
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....
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....
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....
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} Init;
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typedef struct _PCD_DATABSE_UNINIT {
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//==== Following is value structure for PCD without default value
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....
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....
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} UnInit;
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}
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3.3.2 PCD value structure in PCD database C structure
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The value's structure is generated by build tool in PCD database C structure.
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The PCDs in different datum type has different value structure.
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3.3.2.1 UINT8/UINT16/UINT32/UINT64 datum type PCD
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The C structure for these datum type PCD is just a UINT8/UINT16/UINT32/UINT64
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data member in PCD database, For example:
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UINT16 PcdHardwareErrorRecordLevel_d3705011_bc19_4af7_be16_f68030378c15_VariableDefault_0;
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Above structure is generated by build tool, the member name is "PcdCName_Guidvalue"
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Member type is UINT16 according to PcdHardwareErrorRecordLevel declaration
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in DEC file.
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3.3.2.2 VOID* datum type PCD
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The value of VOID* datum type PCD is a UINT8/UINT16 array in PCD database.
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3.3.2.2.1 VOID* - string type
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If the default value for VOID* datum type PCD like L"xxx", the PCD is
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used for unicode string, and C structure of this datum type PCD is
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UINT16 string array in PCD database, for example:
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UINT16 StringTable[29];
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The number of 29 in above sample is max size of a unicode string.
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If the default value for VOID* datum type PCD like "xxx", the PCD is
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used for ascii string, and C structure of this datum type PCD is
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UINT8 string array in PCD database, for example:
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UINT8 StringTable[20];
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The number of 20 in above sample is max size of a ascii string.
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3.3.2.2.2 VOID* - byte array
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If the default value of VOID* datum type PCD like {'0x29', '0x01', '0xf2'}
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the PCD is used for byte array. The generated structrue is same as
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above ascii string table,
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UINT8 StringTable[13];
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The number of 13 in above sample is max size of byte array.
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**/
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