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Diffstat (limited to 'Lesson_22')
| -rw-r--r-- | Lesson_22/README.md | 117 |
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diff --git a/Lesson_22/README.md b/Lesson_22/README.md deleted file mode 100644 index 5280e72..0000000 --- a/Lesson_22/README.md +++ /dev/null @@ -1,117 +0,0 @@ -Let's explore another PCD type - feature flag PCD. - -Add PCD to DEC file UefiLessonsPkg/UefiLessonsPkg.dec: -``` -[PcdsFeatureFlag] - gUefiLessonsPkgTokenSpaceGuid.PcdMyFeatureFlagVar|FALSE|BOOLEAN|0x20000001 -``` - -Populate it to INF UefiLessonsPkg/PCDLesson/PCDLesson.inf: -``` -[FeaturePcd] - gUefiLessonsPkgTokenSpaceGuid.PcdMyFeatureFlagVar -``` - -To get PCD value in a *.c file either `FeaturePcdGet` or `PcdGetBool` can be used which are practically the same https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Library/PcdLib.h: -``` -#define FeaturePcdGet(TokenName) _PCD_GET_MODE_BOOL_##TokenName -#define PcdGetBool(TokenName) _PCD_GET_MODE_BOOL_##TokenName -``` -Let's add both to our UefiLessonsPkg/PCDLesson/PCDLesson.c -``` -Print(L"PcdMyFeatureFlagVar=%d\n", FeaturePcdGet(PcdMyFeatureFlagVar)); -Print(L"PcdMyFeatureFlagVar=%d\n", PcdGetBool(PcdMyFeatureFlagVar)); -``` -Ok, we are ready to build. Build your module and check out AutoGen files. - -Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/AutoGen.h -``` -#define _PCD_TOKEN_PcdMyFeatureFlagVar 0U -#define _PCD_SIZE_PcdMyFeatureFlagVar 1 -#define _PCD_GET_MODE_SIZE_PcdMyFeatureFlagVar _PCD_SIZE_PcdMyFeatureFlagVar -#define _PCD_VALUE_PcdMyFeatureFlagVar ((BOOLEAN)0U) -extern const BOOLEAN _gPcd_FixedAtBuild_PcdMyFeatureFlagVar; -#define _PCD_GET_MODE_BOOL_PcdMyFeatureFlagVar _gPcd_FixedAtBuild_PcdMyFeatureFlagVar -//#define _PCD_SET_MODE_BOOL_PcdMyFeatureFlagVar ASSERT(FALSE) // It is not allowed to set value for a FIXED_AT_BUILD PCD -``` - -Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/AutoGen.c -``` -GLOBAL_REMOVE_IF_UNREFERENCED const BOOLEAN _gPcd_FixedAtBuild_PcdMyFeatureFlagVar = _PCD_VALUE_PcdMyFeatureFlagVar; -``` - -So both calls for our PCD would translate to: -``` -FeaturePcdGet/PcdGetBool(PcdMyFeatureFlagVar) --> _PCD_GET_MODE_BOOL_PcdMyFeatureFlagVar --> _gPcd_FixedAtBuild_PcdMyFeatureFlagVar -``` -And this variable is declared in AutoGen.c file: -``` -GLOBAL_REMOVE_IF_UNREFERENCED const BOOLEAN _gPcd_FixedAtBuild_PcdMyFeatureFlagVar = ((BOOLEAN)0U); -``` - -If you execute it under OVMF these print statements would get you: -``` -PcdMyFeatureFlagVar=0 -PcdMyFeatureFlagVar=0 -``` - -________________________ - -So as you can see a feature PCD is similar to a BOOLEAN PCD defined under `PcdsFixedAtBuild` section - -Let's create a fixed bool PCD and compare results: - -UefiLessonsPkg/UefiLessonsPkg.dec: -``` -[PcdsFixedAtBuild] - ... - gUefiLessonsPkgTokenSpaceGuid.PcdMyVarBool|FALSE|BOOLEAN|0x00000004 - -[PcdsFeatureFlag] - gUefiLessonsPkgTokenSpaceGuid.PcdMyFeatureFlagVar|FALSE|BOOLEAN|0x20000001 -``` -UefiLessonsPkg/PCDLesson/PCDLesson.inf: -``` -[FixedPcd] - ... - gUefiLessonsPkgTokenSpaceGuid.PcdMyVarBool - -[FeaturePcd] - gUefiLessonsPkgTokenSpaceGuid.PcdMyFeatureFlagVar -``` -UefiLessonsPkg/PCDLesson/PCDLesson.c: -``` -Print(L"PcdMyFeatureFlagVar=%d\n", FeaturePcdGet(PcdMyFeatureFlagVar)); -Print(L"PcdMyFeatureFlagVar=%d\n", PcdGetBool(PcdMyFeatureFlagVar)); -Print(L"PcdMyVarBool=%d\n", FixedPcdGetBool(PcdMyVarBool)); -Print(L"PcdMyVarBool=%d\n", PcdGetBool(PcdMyVarBool)); -``` - -Ok, now let's build and look at AutoGen files: - -AutoGen.c -``` -GLOBAL_REMOVE_IF_UNREFERENCED const BOOLEAN _gPcd_FixedAtBuild_PcdMyVarBool = _PCD_VALUE_PcdMyVarBool; -GLOBAL_REMOVE_IF_UNREFERENCED const BOOLEAN _gPcd_FixedAtBuild_PcdMyFeatureFlagVar = _PCD_VALUE_PcdMyFeatureFlagVar; -``` -AutoGen.h -``` -#define _PCD_TOKEN_PcdMyVarBool 0U -#define _PCD_SIZE_PcdMyVarBool 1 -#define _PCD_GET_MODE_SIZE_PcdMyVarBool _PCD_SIZE_PcdMyVarBool -#define _PCD_VALUE_PcdMyVarBool 0U -extern const BOOLEAN _gPcd_FixedAtBuild_PcdMyVarBool; -#define _PCD_GET_MODE_BOOL_PcdMyVarBool _gPcd_FixedAtBuild_PcdMyVarBool -//#define _PCD_SET_MODE_BOOL_PcdMyVarBool ASSERT(FALSE) // It is not allowed to set value for a FIXED_AT_BUILD PCD - -#define _PCD_TOKEN_PcdMyFeatureFlagVar 0U -#define _PCD_SIZE_PcdMyFeatureFlagVar 1 -#define _PCD_GET_MODE_SIZE_PcdMyFeatureFlagVar _PCD_SIZE_PcdMyFeatureFlagVar -#define _PCD_VALUE_PcdMyFeatureFlagVar ((BOOLEAN)0U) -extern const BOOLEAN _gPcd_FixedAtBuild_PcdMyFeatureFlagVar; -#define _PCD_GET_MODE_BOOL_PcdMyFeatureFlagVar _gPcd_FixedAtBuild_PcdMyFeatureFlagVar -//#define _PCD_SET_MODE_BOOL_PcdMyFeatureFlagVar ASSERT(FALSE) // It is not allowed to set value for a FIXED_AT_BUILD PCD -``` - -As you see the differences are subtle. `FeaturePcd` is simply a syntactic sugar for BOOLEAN `FixedAtBuild` PCD. - |