X-Git-Url: https://gerrit.automotivelinux.org/gerrit/gitweb?a=blobdiff_plain;f=docs%2Findex.rst;h=31d781ea74d64d62033b0c1d7eaad59b4b420985;hb=e18352d50678005c9dbb3ac76913555f5317c81c;hp=93b06e86a9835a5e3182575a8990632219d48389;hpb=09f92bafa59460ea4597c557e469e982386c9e3b;p=apps%2Fagl-service-can-low-level.git

diff --git a/docs/index.rst b/docs/index.rst
index 93b06e86..31d781ea 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -2,6 +2,8 @@
 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.
 
@@ -11,20 +13,22 @@ 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*.
+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.
 
-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 string *nanopb_generator.py* accomplishes this.
+.. image:: generator_flow.png
 
 So a typical project might include these files:
 
 1) Nanopb runtime library:
     - pb.h
-    - pb_decode.h and pb_decode.c
-    - pb_encode.h and pb_encode.c
+    - 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
-    - person.c (autogenerated, contains initializers for const arrays)
-    - person.h (autogenerated, contains type declarations)
+    - person.proto (just an example)
+    - person.pb.c (autogenerated, contains initializers for const arrays)
+    - person.pb.h (autogenerated, contains type declarations)
 
 Features and limitations
 ========================
@@ -35,15 +39,20 @@ Features and limitations
 #) Small code size (2–10 kB depending on processor)
 #) Small ram usage (typically 200 bytes)
 #) Allows specifying maximum size for strings and arrays, so that they can be allocated statically.
-#) No malloc needed: everything is stored on the stack.
+#) No malloc needed: everything can be allocated statically or on the stack.
 #) You can use either encoder or decoder alone to cut the code size in half.
 
 **Limitations**
 
-#) User must provide callbacks when decoding arrays or strings without maximum size.
+#) User must provide callbacks when decoding arrays or strings without maximum size. Malloc support could be added as a separate module.
 #) Some speed has been sacrificed for code size. For example varint calculations are always done in 64 bits.
 #) 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. This causes incompatibility with decoders that do not support packed format.
+#) Cyclic references between messages are not supported. They could be supported in callback-mode if there was an option in the generator to set the mode.
 
 Getting started
 ===============
@@ -54,8 +63,12 @@ For starters, consider this simple message::
     required int32 value = 1;
  }
 
-Save this in *example.proto* and run it through *nanopb_generate.py*. You
-should now have in *example.h*::
+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;
@@ -72,21 +85,29 @@ Now in your main program do this to encode a message::
 
 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 example.proto* to verify its validity.
+You can feed the message to *protoc --decode=Example message.proto* to verify its validity.
 
-Library reference
-=================
+For complete examples of the simple cases, see *tests/test_decode1.c* and *tests/test_encode1.c*. For an example with network interface, see the *example* subdirectory.
+
+Compiler requirements
+=====================
+Nanopb should compile with most ansi-C compatible compilers. It however requires a few header files to be available:
 
-**Encoding**
+#) *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*
 
-**Decoding**
+If these header files do not come with your compiler, you should be able to find suitable replacements online. Mostly the requirements are very simple, just a few basic functions and typedefs.
 
-**Specifying field options**
+Debugging and testing
+=====================
+Extensive unittests are included under the *tests* folder. Just type *make* there to run the tests.
 
-**Generated code**
+This also generates a file called *breakpoints* which includes all lines returning *false* in nanopb. You can use this in gdb by typing *source breakpoints*, after which gdb will break on first nanopb error.
 
 Wishlist
 ========
 #) A specialized encoder for encoding to a memory buffer. Should serialize in reverse order to avoid having to determine submessage size beforehand.
-#) A cleaner rewrite of the source generator.
-#) Better performance for 16- and 8-bit platforms.
+#) A cleaner rewrite of the Python-based source generator.
+#) Better performance for 16- and 8-bit platforms: use smaller datatypes where possible.