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| -rw-r--r-- | Lessons_uncategorized/Lesson_PCD_HII/README.md | 26 |
1 files changed, 14 insertions, 12 deletions
diff --git a/Lessons_uncategorized/Lesson_PCD_HII/README.md b/Lessons_uncategorized/Lesson_PCD_HII/README.md index 08f5000..da97b75 100644 --- a/Lessons_uncategorized/Lesson_PCD_HII/README.md +++ b/Lessons_uncategorized/Lesson_PCD_HII/README.md @@ -23,12 +23,12 @@ So far we've worked only with `Default` PCDs. Initial values for these PCDs are Now let's try to investigate `Hii` PCDs. -For this storage method PCD are declared this way: +For this storage method PCDs are declared this way: ``` <TokenGuid>.<TokenName>|<EFI Var Name>|<EFI Var GUID>|<Offset in EFI Var>[|<Override value>[|<EFI Var attributes>]] ``` -For example let's use this code in the DSC file +For example let's use this code in the DSC file: ``` [PcdsDynamicHii] gUefiLessonsPkgTokenSpaceGuid.PcdDynamicInt32|L"MyHiiVar"|gUefiLessonsPkgTokenSpaceGuid|0x5|0x11111111|BS,RT @@ -36,10 +36,10 @@ For example let's use this code in the DSC file [PcdsDynamicExHii] gUefiLessonsPkgTokenSpaceGuid.PcdDynamicExInt32|L"MyExHiiVar"|gUefiLessonsPkgTokenSpaceGuid|0x7|0x22222222|BS ``` -Here we've used the same GUID for the EFI var as we use for the PCD token space, but this is not mondatory. +Here we've used the same GUID for the EFI var that we use for the PCD token space, but you should know that it is not mandatory. -Now additionaly correct PCDLesson application, so it would only get these PCDs, without any modifications: -``` +Now additionaly correct `PCDLesson` application, so it would only get these PCDs, without any modifications: +```cpp if (PcdToken(PcdDynamicInt32)) { Print(L"PcdDynamicInt32=0x%x\n", PcdGet32(PcdDynamicInt32)); } else { @@ -100,6 +100,8 @@ Value: 0x22222222 (=572662306) ``` +You can see that now our PCDs are encoded completely differently in the PCD database. + Now launch OVMF. You can check `DumpDynPcd.efi` output, but it doesn't show anything specific about the PCD storage methood: ``` FS0:\> DumpDynPcd.efi @@ -117,7 +119,7 @@ FS0:\> dmpstore -guid 150cab53-ad47-4385-b5dd-bcfc76bacaf0 dmpstore: No matching variables found. Guid 150CAB53-AD47-4385-B5DD-BCFC76BACAF0 ``` -So out PCDs didn't create any variables. +So our PCDs didn't create any EFI variables. Let's execute our `PCDLesson.efi` application that right now only use `PcdGet*` functions: ``` @@ -133,10 +135,10 @@ FS0:\> dmpstore -guid 150cab53-ad47-4385-b5dd-bcfc76bacaf0 dmpstore: No matching variables found. Guid 150CAB53-AD47-4385-B5DD-BCFC76BACAF0 ``` -The point of this is that simple `PcdGet*` doesn't work with EFI variable interface if there is no EFI variable beforehand. In this case `PcdGet*` simply returns default value from the PCD Database. +The point of this is that `PcdGet*` doesn't work with the EFI variable interface if there is no EFI variable beforehand. In this case `PcdGet*` simply returns default value from the PCD Database. -Now let's return the `PcdSet*` code to out `PCDLesson.efi` application: -``` +Now let's return the `PcdSet*` code to our `PCDLesson.efi` application: +```cpp if (PcdToken(PcdDynamicInt32)) { Print(L"PcdDynamicInt32=0x%x\n", PcdGet32(PcdDynamicInt32)); Status = PcdSet32S(PcdDynamicInt32, 0xBEEFBEEF); @@ -183,7 +185,7 @@ Variable RT+BS '150CAB53-AD47-4385-B5DD-BCFC76BACAF0:MyHiiVar' DataSize = 0x09 As you can see the `PcdSet*` statements have created EFI variables that were not present before. The variables were created with a minimal possible size = `Offset in EFI Var` + `sizeof(value)`. In our case it is `5 + 4 = 9 = 0x09` and `7 + 4 = 11 = 0x0B`. -You can see how all the field from the PCD statement in the DSC are transformed to the EFI variable settings. +You can see how all the fields from the PCD statement in the DSC are transformed to the EFI variable settings. # `Non-volatile` variables @@ -230,7 +232,7 @@ Variable NV+RT+BS '150CAB53-AD47-4385-B5DD-BCFC76BACAF0:MyHiiVar' DataSize = 0x0 00000000: 00 00 00 00 00 EF BE EF-BE *.........* ``` -As you can see now it is present from the start. And `PcdGet*`/`PcdSet*` functions successfully use it: +As you can see now the EFI variables are present from the start. And `PcdGet*`/`PcdSet*` functions successfully use their content: ``` FS0:\> PCDLesson.efi ... @@ -247,7 +249,7 @@ So the PCD default values are used only if there is no EFI variable. If the acco # Simplified override -It is possible to omit EFI variable attributes or value override in the PCD desclaration. For example: +It is possible to omit EFI variable attributes or value override in the PCD declaration. For example: ``` [PcdsDynamicHii] gUefiLessonsPkgTokenSpaceGuid.PcdDynamicInt32|L"MyHiiVar"|gUefiLessonsPkgTokenSpaceGuid|0x5 |