[edk2-VfrSpecification PATCH V2] Add union data type and bit fields in VFR Data Struct Definition

[Dandan Bi <dandan.bi@intel.com>]

V2: Add a note in the doc:for the bit field, the number of
the bit width could not exceed 32.

https://bugzilla.tianocore.org/show_bug.cgi?id=683

Cc: Eric Dong <eric.dong@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by:  Eric Dong <eric.dong@intel.com>
---
 .../23_vfr_data_struct_definition.md               | 40 ++++++++++++++++++++++
 README.md                                          |  1 +
 2 files changed, 41 insertions(+)

diff --git a/2_vfr_description_in_bnf/23_vfr_data_struct_definition.md b/2_vfr_description_in_bnf/23_vfr_data_struct_definition.md
index 6d6730d..2769d4f 100644
--- a/2_vfr_description_in_bnf/23_vfr_data_struct_definition.md
+++ b/2_vfr_description_in_bnf/23_vfr_data_struct_definition.md
@@ -36,10 +36,16 @@ vfrDataStructDefinition ::=
  { "typedef" } "struct"
  { StringIdentifier }
  "{" vfrDataStructFields "}"
  { StringIdentifier } ";"
 
+vfrDataStructDefinition ::=
+ { "typedef" } "union"
+ { StringIdentifier }
+ "{" vfrDataStructFields "}"
+ { StringIdentifier } ";"
+
 vfrDataStructFields ::=
   (
       dataStructField64
     | dataStructField32
     | dataStructField16
@@ -48,10 +54,14 @@ vfrDataStructFields ::=
     | dataStructFieldString
     | dataStructFieldDate
     | dataStructFieldTime
     | dataStructFieldRef
     | dataStructFieldUser
+    | dataStructBitField64
+    | dataStructBitField32
+    | dataStructBitField16
+    | dataStructBitField8
   )*
 
 dataStructField64 ::=
   "UINT64"
   StringIdentifier { "[" Number "]" } ";"
@@ -89,29 +99,59 @@ dataStructFieldRef ::=
   StringIdentifier { "[" Number "]" } ";"
 
 dataStructFieldUser ::=
   StringIdentifier
   StringIdentifier { "[" Number "]" } ";"
+
+dataStructBitField64 ::=
+  "UINT64"
+  { StringIdentifier } ":" Number ";"
+
+dataStructBitField32 ::=
+  "UINT32"
+  { StringIdentifier } ":" Number ";"
+
+dataStructBitField16 ::=
+  "UINT16"
+  { StringIdentifier } ":" Number ";"
+
+dataStructBitField8 ::=
+  "UINT8"
+  { StringIdentifier } ":" Number ";"
 ```
 
 #### BEHAVIORS AND RESTRICTIONS
 
 The data structure definition is in C-style language. `enum` type is not
 supported. The keyword of the fields' type must be a user defined data
 structure or one of these types: `UINT8`, `UINT16`, `UINT32`, `UINT64`,
 `BOOLEAN`, `EFI_STRING_ID`, `EFI_HII_DATA`, `EFI_HII_TIME EFI_HII_REF`, and at
 most one-dimensional array is permitted.
+Note: for the bit field, the number of the bit width could not exceed 32.
 
 #### Example
 
 ```c
 typedef struct {
   UINT8 mU8;
   UINT16 mU16;
   UINT32 mU32[10];
   UINT64 mU64;
 } MyData;
+
+typedef union {
+  UINT16   Field16;
+  UINT8    Field8;
+} MyUnionData;
+
+typedef struct {
+  UINT16   Field16;
+  UINT8    MyBits1 : 1;
+  UINT8    MyBits2 : 3;
+  UINT8    MyBits3 : 3;
+  UINT16   MyBits4 : 4;
+} MyBitsData;
 ```
 
 **Unsupported Example of enum type:**
 
 ```c
diff --git a/README.md b/README.md
index 888eb81..0a596eb 100644
--- a/README.md
+++ b/README.md
@@ -89,5 +89,6 @@ Copyright (c) 2007-2017, Intel Corporation. All rights reserved.
 | 1.60     | Update syntax for goto, image, questionref and constant value opcodes, correct CALLBACK flag to INTEREACTIVE, correct help string for old syntax date/time example, and add examples for expression opcodes.   | December 1, 2011  |
 | 1.70     | Clarify restriction that enum type and struct data filed with more than one dimensions array are not supported.                                                                                                | May 18, 2012      |
 | 1.80     | Add syntax for warningif opcode, update definition for name/value varstore and subtitle opcode, update referenced UEFI spec version info.                                                                      | Jan 14, 2014      |
 | 1.90     | Correct sample code for catenate/match/cond opcode. Add syntax for match2 opcode. Add sample code to show the buffer type constant value for orderedlist opcode and default opcode.                            | July 2, 2015      |
 | 1.91     | Convert to Gitbook                                                                                                                                                                                             | April 2017        |
+|          | [#683](https://bugzilla.tianocore.org/show_bug.cgi?id=683) VFR Spec: Add union data type and bit fields in VFR Data Struct Definition                                                                          |                   |
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