Loading tools/pdl/doc/reference.md +47 −0 Original line number Diff line number Diff line Loading @@ -54,6 +54,53 @@ packet Brew { } ``` The endianess affects how fields of fractional bit-size (hence named bit-fields) are parsed or serialized. Such fields are grouped together to the next byte boundary, least significant bit first, and then byte-swapped to the required endianess before being written to memory, or after being read from memory. ``` packet Coffee { a: 1, b: 15, c: 3, d: 5, } // Little endian layout // LSB MSB // 0 1 2 3 4 5 6 7 // +---------------------------------------+ // 0 | a | b[6:0] | // +---------------------------------------+ // 1 | b[14:7] | // +---------------------------------------+ // 2 | c | d | // +---------------------------------------+ // Big endian layout // LSB MSB // 0 1 2 3 4 5 6 7 // +---------------------------------------+ // 0 | b[14:7] | // +---------------------------------------+ // 1 | a | b[6:0] | // +---------------------------------------+ // 2 | c | d | // +---------------------------------------+ ``` Fields which qualify as bit-fields are: - [Scalar](#fields-scalar) fields - [Size](#fields-size) fields - [Count](#fields-count) fields - [Fixed](#fields-fixed) fields - [Reserved](#fields-reserved) fields - [Typedef](#fields-typedef) fields, when the field type is an [Enum](#enum) Fields that do not qualify as bit-fields _must_ start and end on a byte boundary. ## Identifiers - Identifiers can denote a field; an enumeration tag; or a declared type. Loading Loading
tools/pdl/doc/reference.md +47 −0 Original line number Diff line number Diff line Loading @@ -54,6 +54,53 @@ packet Brew { } ``` The endianess affects how fields of fractional bit-size (hence named bit-fields) are parsed or serialized. Such fields are grouped together to the next byte boundary, least significant bit first, and then byte-swapped to the required endianess before being written to memory, or after being read from memory. ``` packet Coffee { a: 1, b: 15, c: 3, d: 5, } // Little endian layout // LSB MSB // 0 1 2 3 4 5 6 7 // +---------------------------------------+ // 0 | a | b[6:0] | // +---------------------------------------+ // 1 | b[14:7] | // +---------------------------------------+ // 2 | c | d | // +---------------------------------------+ // Big endian layout // LSB MSB // 0 1 2 3 4 5 6 7 // +---------------------------------------+ // 0 | b[14:7] | // +---------------------------------------+ // 1 | a | b[6:0] | // +---------------------------------------+ // 2 | c | d | // +---------------------------------------+ ``` Fields which qualify as bit-fields are: - [Scalar](#fields-scalar) fields - [Size](#fields-size) fields - [Count](#fields-count) fields - [Fixed](#fields-fixed) fields - [Reserved](#fields-reserved) fields - [Typedef](#fields-typedef) fields, when the field type is an [Enum](#enum) Fields that do not qualify as bit-fields _must_ start and end on a byte boundary. ## Identifiers - Identifiers can denote a field; an enumeration tag; or a declared type. Loading
