Separation Generator to a dedicated repo

Change-Id: Id94831651c3266861435272a6e36c7884bef2c45
Signed-off-by: Romain Forlot <romain.forlot@iot.bzh>

1 files changed, 127 insertions, 0 deletions

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+=============================================
+Nanopb: Protocol Buffers with small code size
+=============================================
+
+.. include :: menu.rst
+
+Nanopb is an ANSI-C library for encoding and decoding messages in Google's `Protocol Buffers`__ format with minimal requirements for RAM and code space.
+It is primarily suitable for 32-bit microcontrollers.
+
+__ https://developers.google.com/protocol-buffers/docs/reference/overview
+
+Overall structure
+=================
+
+For the runtime program, you always need *pb.h* for type declarations.
+Depending on whether you want to encode, decode, or both, you also need *pb_encode.h/c* or *pb_decode.h/c*.
+
+The high-level encoding and decoding functions take an array of *pb_field_t* structures, which describes the fields of a message structure. Usually you want these autogenerated from a *.proto* file. The tool script *nanopb_generator.py* accomplishes this.
+
+.. image:: generator_flow.png
+
+So a typical project might include these files:
+
+1) Nanopb runtime library:
+    - pb.h
+    - pb_common.h and pb_common.c (always needed)
+    - pb_decode.h and pb_decode.c (needed for decoding messages)
+    - pb_encode.h and pb_encode.c (needed for encoding messages)
+2) Protocol description (you can have many):
+    - person.proto (just an example)
+    - person.pb.c (autogenerated, contains initializers for const arrays)
+    - person.pb.h (autogenerated, contains type declarations)
+
+Features and limitations
+========================
+
+**Features**
+
+#) Pure C runtime
+#) Small code size (2–10 kB depending on processor, plus any message definitions)
+#) Small ram usage (typically ~300 bytes, plus any message structs)
+#) Allows specifying maximum size for strings and arrays, so that they can be allocated statically.
+#) No malloc needed: everything can be allocated statically or on the stack. Optional malloc support available.
+#) You can use either encoder or decoder alone to cut the code size in half.
+#) Support for most protobuf features, including: all data types, nested submessages, default values, repeated and optional fields, oneofs, packed arrays, extension fields.
+#) Callback mechanism for handling messages larger than can fit in available RAM.
+#) Extensive set of tests.
+
+**Limitations**
+
+#) Some speed has been sacrificed for code size.
+#) Encoding is focused on writing to streams. For memory buffers only it could be made more efficient.
+#) The deprecated Protocol Buffers feature called "groups" is not supported.
+#) Fields in the generated structs are ordered by the tag number, instead of the natural ordering in .proto file.
+#) Unknown fields are not preserved when decoding and re-encoding a message.
+#) Reflection (runtime introspection) is not supported. E.g. you can't request a field by giving its name in a string.
+#) Numeric arrays are always encoded as packed, even if not marked as packed in .proto.
+#) Cyclic references between messages are supported only in callback and malloc mode.
+
+Getting started
+===============
+
+For starters, consider this simple message::
+
+ message Example {
+    required int32 value = 1;
+ }
+
+Save this in *message.proto* and compile it::
+
+    user@host:~$ protoc -omessage.pb message.proto
+    user@host:~$ python nanopb/generator/nanopb_generator.py message.pb
+
+You should now have in *message.pb.h*::
+
+ typedef struct {
+    int32_t value;
+ } Example;
+ 
+ extern const pb_field_t Example_fields[2];
+
+Now in your main program do this to encode a message::
+
+ Example mymessage = {42};
+ uint8_t buffer[10];
+ pb_ostream_t stream = pb_ostream_from_buffer(buffer, sizeof(buffer));
+ pb_encode(&stream, Example_fields, &mymessage);
+
+After that, buffer will contain the encoded message.
+The number of bytes in the message is stored in *stream.bytes_written*.
+You can feed the message to *protoc --decode=Example message.proto* to verify its validity.
+
+For a complete example of the simple case, see *example/simple.c*.
+For a more complex example with network interface, see the *example/network_server* subdirectory.
+
+Compiler requirements
+=====================
+Nanopb should compile with most ansi-C compatible compilers. It however
+requires a few header files to be available:
+
+#) *string.h*, with these functions: *strlen*, *memcpy*, *memset*
+#) *stdint.h*, for definitions of *int32_t* etc.
+#) *stddef.h*, for definition of *size_t*
+#) *stdbool.h*, for definition of *bool*
+
+If these header files do not come with your compiler, you can use the
+file *extra/pb_syshdr.h* instead. It contains an example of how to provide
+the dependencies. You may have to edit it a bit to suit your custom platform.
+
+To use the pb_syshdr.h, define *PB_SYSTEM_HEADER* as *"pb_syshdr.h"* (including the quotes).
+Similarly, you can provide a custom include file, which should provide all the dependencies
+listed above.
+
+Running the test cases
+======================
+Extensive unittests and test cases are included under the *tests* folder.
+
+To build the tests, you will need the `scons`__ build system. The tests should
+be runnable on most platforms. Windows and Linux builds are regularly tested.
+
+__ http://www.scons.org/
+
+In addition to the build system, you will also need a working Google Protocol
+Buffers *protoc* compiler, and the Python bindings for Protocol Buffers. On
+Debian-based systems, install the following packages: *protobuf-compiler*,
+*python-protobuf* and *libprotobuf-dev*.
+