X-Git-Url: https://gerrit.automotivelinux.org/gerrit/gitweb?a=blobdiff_plain;f=docs%2Freference.rst;h=6094e13c900bc68a4d0fad884d853767ea03a41d;hb=6e9e5329278b04a8e76d63f06fed2f3bfa80e2f8;hp=fee1b702cb93e3441e32967370ec7a8fbf115896;hpb=4ba6a3027d7a5d8c17abeb031622389f8be234fe;p=apps%2Fagl-service-can-low-level.git diff --git a/docs/reference.rst b/docs/reference.rst index fee1b702..6094e13c 100644 --- a/docs/reference.rst +++ b/docs/reference.rst @@ -6,29 +6,160 @@ Nanopb: API reference .. contents :: + + + Compilation options =================== -The following options can be specified using -D switch given to the C compiler: - -============================ ================================================================================================ -__BIG_ENDIAN__ Set this if your platform stores integers and floats in big-endian format. - Mixed-endian systems (different layout for ints and floats) are currently not supported. -NANOPB_INTERNALS Set this to expose the field encoder functions that are hidden since nanopb-0.1.3. -PB_MAX_REQUIRED_FIELDS Maximum number of required fields to check for presence. Default value is 64. Increases stack - usage 1 byte per every 8 fields. Compiler warning will tell if you need this. -PB_FIELD_16BIT Add support for tag numbers > 255 and fields larger than 255 bytes or 255 array entries. - Increases code size 3 bytes per each field. Compiler error will tell if you need this. -PB_FIELD_32BIT Add support for tag numbers > 65535 and fields larger than 65535 bytes or 65535 array entries. - Increases code size 9 bytes per each field. Compiler error will tell if you need this. -PB_NO_ERRMSG Disables the support for error messages; only error information is the true/false return value. - Decreases the code size by a few hundred bytes. -PB_BUFFER_ONLY Disables the support for custom streams. Only supports encoding to memory buffers. - Speeds up execution and decreases code size slightly. -============================ ================================================================================================ - -The PB_MAX_REQUIRED_FIELDS, PB_FIELD_16BIT and PB_FIELD_32BIT settings allow raising some datatype limits to suit larger messages. -Their need is recognized automatically by C-preprocessor #if-directives in the generated .pb.h files. The default setting is to use -the smallest datatypes (least resources used). +The following options can be specified using -D switch given to the C compiler +when compiling the nanopb library and applications using it. You must have the +same settings for the nanopb library and all code that includes pb.h. + +============================ ================================================ +__BIG_ENDIAN__ Set this if your platform stores integers and + floats in big-endian format. Mixed-endian + systems (different layout for ints and floats) + are currently not supported. +NANOPB_INTERNALS Set this to expose the field encoder functions + that are hidden since nanopb-0.1.3. +PB_MAX_REQUIRED_FIELDS Maximum number of required fields to check for + presence. Default value is 64. Increases stack + usage 1 byte per every 8 fields. Compiler + warning will tell if you need this. +PB_FIELD_16BIT Add support for tag numbers > 255 and fields + larger than 255 bytes or 255 array entries. + Increases code size 3 bytes per each field. + Compiler error will tell if you need this. +PB_FIELD_32BIT Add support for tag numbers > 65535 and fields + larger than 65535 bytes or 65535 array entries. + Increases code size 9 bytes per each field. + Compiler error will tell if you need this. +PB_NO_ERRMSG Disables the support for error messages; only + error information is the true/false return + value. Decreases the code size by a few hundred + bytes. +PB_BUFFER_ONLY Disables the support for custom streams. Only + supports encoding and decoding with memory + buffers. Speeds up execution and decreases code + size slightly. +PB_OLD_CALLBACK_STYLE Use the old function signature (void\* instead + of void\*\*) for callback fields. This was the + default until nanopb-0.2.1. +============================ ================================================ + +The PB_MAX_REQUIRED_FIELDS, PB_FIELD_16BIT and PB_FIELD_32BIT settings allow +raising some datatype limits to suit larger messages. Their need is recognized +automatically by C-preprocessor #if-directives in the generated .pb.h files. +The default setting is to use the smallest datatypes (least resources used). + + + + +Proto file options +================== +The generator behaviour can be adjusted using these options, defined in the +'nanopb.proto' file in the generator folder: + +============================ ================================================ +max_size Allocated size for 'bytes' and 'string' fields. +max_count Allocated number of entries in arrays + ('repeated' fields). +type Type of the generated field. Default value + is FT_DEFAULT, which selects automatically. + You can use FT_CALLBACK, FT_STATIC or FT_IGNORE + to force a callback field, a static field or + to completely ignore the field. +long_names Prefix the enum name to the enum value in + definitions, i.e. 'EnumName_EnumValue'. Enabled + by default. +packed_struct Make the generated structures packed. + NOTE: This cannot be used on CPUs that break + on unaligned accesses to variables. +============================ ================================================ + +These options can be defined for the .proto files before they are converted +using the nanopb-generatory.py. There are three ways to define the options: + +1. Using a separate .options file. + This is the preferred way as of nanopb-0.2.1, because it has the best + compatibility with other protobuf libraries. +2. Defining the options on the command line of nanopb_generator.py. + This only makes sense for settings that apply to a whole file. +3. Defining the options in the .proto file using the nanopb extensions. + This is the way used in nanopb-0.1, and will remain supported in the + future. It however sometimes causes trouble when using the .proto file + with other protobuf libraries. + +The effect of the options is the same no matter how they are given. The most +common purpose is to define maximum size for string fields in order to +statically allocate them. + +Defining the options in a .options file +--------------------------------------- +The preferred way to define options is to have a separate file +'myproto.options' in the same directory as the 'myproto.proto'. The +generator will automatically search for this file and read the options from +it. The file format is as follows: + +* Lines starting with '#' or '//' are regarded as comments. +* Blank lines are ignored. +* All other lines should start with a field name pattern, followed by one or + more options. For example: *"MyMessage.myfield max_size:5 max_count:10"*. +* The field name pattern is matched against a string of form 'Message.field'. + For nested messages, the string is 'Message.SubMessage.field'. +* The field name pattern may use the notation recognized by Python fnmatch(): + - \* matches any part of string, like 'Message.\*' for all fields + - \? matches any single character + - [seq] matches any of characters 's', 'e' and 'q' + - [!seq] matches any other character +* The options are written as 'option_name:option_value' and several options + can be defined on same line, separated by whitespace. +* Options defined later in the file override the ones specified earlier, so + it makes sense to define wildcard options first in the file and more specific + ones later. + +If preferred, the name of the options file can be set using the command line +switch '-f' to nanopb_generator.py. + +Defining the options on command line +------------------------------------ +The nanopb_generator.py has a simple command line option '-s OPTION:VALUE'. +The setting applies to the whole file that is being processed. + +Defining the options in the .proto file +--------------------------------------- +The .proto file format allows defining custom options for the fields. +The nanopb library comes with 'nanopb.proto' which does exactly that, allowing +you do define the options directly in the .proto file: + + import "nanopb.proto"; + required string name = 1 [(nanopb).max_size = 40]; + repeated PhoneNumber phone = 4 [(nanopb).max_count = 5]; + +A small complication is that you have to set the include path of protoc so that +nanopb.proto can be found. This file, in turn, requires the file +*google/protobuf/descriptor.proto*. This is usually installed under +*/usr/include*. Therefore, to compile a .proto file which uses options, use a +protoc command similar to:: + + protoc -I/usr/include -Inanopb/generator -I. -omessage.pb message.proto + +The options can be defined in file, message and field scopes:: + + option (nanopb_fileopt).max_size = 20; // File scope + message Message + { + option (nanopb_msgopt).max_size = 30; // Message scope + required string fieldsize = 1 [(nanopb).max_size = 40]; // Field scope + } + + + + + + + + pb.h ==== @@ -37,22 +168,23 @@ pb_type_t --------- Defines the encoder/decoder behaviour that should be used for a field. :: - typedef enum { ... } pb_type_t; + typedef uint8_t pb_type_t; -The low-order byte of the enumeration values defines the function that can be used for encoding and decoding the field data: +The low-order nibble of the enumeration values defines the function that can be used for encoding and decoding the field data: ==================== ===== ================================================ LTYPE identifier Value Storage format ==================== ===== ================================================ PB_LTYPE_VARINT 0x00 Integer. PB_LTYPE_SVARINT 0x01 Integer, zigzag encoded. -PB_LTYPE_FIXED 0x02 Integer or floating point. -PB_LTYPE_BYTES 0x03 Structure with *size_t* field and byte array. -PB_LTYPE_STRING 0x04 Null-terminated string. -PB_LTYPE_SUBMESSAGE 0x05 Submessage structure. +PB_LTYPE_FIXED32 0x02 32-bit integer or floating point. +PB_LTYPE_FIXED64 0x03 64-bit integer or floating point. +PB_LTYPE_BYTES 0x04 Structure with *size_t* field and byte array. +PB_LTYPE_STRING 0x05 Null-terminated string. +PB_LTYPE_SUBMESSAGE 0x06 Submessage structure. ==================== ===== ================================================ -The high-order byte defines whether the field is required, optional, repeated or callback: +The bits 4-5 define whether the field is required, optional or repeated: ==================== ===== ================================================ HTYPE identifier Value Field handling @@ -60,12 +192,23 @@ HTYPE identifier Value Field handling PB_HTYPE_REQUIRED 0x00 Verify that field exists in decoded message. PB_HTYPE_OPTIONAL 0x10 Use separate *has_* boolean to specify whether the field is present. -PB_HTYPE_ARRAY 0x20 A repeated field with preallocated array. + (Unless it is a callback) +PB_HTYPE_REPEATED 0x20 A repeated field with preallocated array. Separate *_count* for number of items. -PB_HTYPE_CALLBACK 0x30 A field with dynamic storage size, data is - actually a pointer to a structure containing a - callback function. + (Unless it is a callback) +==================== ===== ================================================ + +The bits 6-7 define the how the storage for the field is allocated: + +==================== ===== ================================================ +ATYPE identifier Value Allocation method ==================== ===== ================================================ +PB_ATYPE_STATIC 0x00 Statically allocated storage in the structure. +PB_ATYPE_CALLBACK 0x40 A field with dynamic storage size. Struct field + actually contains a pointer to a callback + function. +==================== ===== ================================================ + pb_field_t ---------- @@ -83,7 +226,7 @@ Describes a single structure field with memory position in relation to others. T } pb_packed; :tag: Tag number of the field or 0 to terminate a list of fields. -:type: LTYPE and HTYPE of the field. +:type: LTYPE, HTYPE and ATYPE of the field. :data_offset: Offset of field data, relative to the end of the previous field. :size_offset: Offset of *bool* flag for optional fields or *size_t* count for arrays, relative to field data. :data_size: Size of a single data entry, in bytes. For PB_LTYPE_BYTES, the size of the byte array inside the containing structure. For PB_HTYPE_CALLBACK, size of the C data type if known. @@ -110,14 +253,16 @@ Part of a message structure, for fields with type PB_HTYPE_CALLBACK:: typedef struct _pb_callback_t pb_callback_t; struct _pb_callback_t { union { - bool (*decode)(pb_istream_t *stream, const pb_field_t *field, void *arg); - bool (*encode)(pb_ostream_t *stream, const pb_field_t *field, const void *arg); + bool (*decode)(pb_istream_t *stream, const pb_field_t *field, void **arg); + bool (*encode)(pb_ostream_t *stream, const pb_field_t *field, void * const *arg); } funcs; void *arg; }; -The *arg* is passed to the callback when calling. It can be used to store any information that the callback might need. +A pointer to the *arg* is passed to the callback when calling. It can be used to store any information that the callback might need. + +Previously the function received just the value of *arg* instead of a pointer to it. This old behaviour can be enabled by defining *PB_OLD_CALLBACK_STYLE*. When calling `pb_encode`_, *funcs.encode* is used, and similarly when calling `pb_decode`_, *funcs.decode* is used. The function pointers are stored in the same memory location but are of incompatible types. You can set the function pointer to NULL to skip the field. @@ -132,6 +277,16 @@ Protocol Buffers wire types. These are used with `pb_encode_tag`_. :: PB_WT_32BIT = 5 } pb_wire_type_t; + + + + + + + + + + pb_encode.h =========== @@ -281,6 +436,17 @@ In Protocol Buffers format, the submessage size must be written before the subme If the submessage contains callback fields, the callback function might misbehave and write out a different amount of data on the second call. This situation is recognized and *false* is returned, but garbage will be written to the output before the problem is detected. + + + + + + + + + + + pb_decode.h ===========