examples: Add example code for user C modules, both C and C++.

Add working example code to provide a starting point for users with files
that they can just copy, and include the modules in the coverage test to
verify the complete user C module build functionality.  The cexample module
uses the code originally found in cmodules.rst, which has been updated to
reflect this and partially rewritten with more complete information.

4 files changed, 59 insertions, 0 deletions

diff --git a/examples/usercmodule/cppexample/example.cpp b/examples/usercmodule/cppexample/example.cpp
new file mode 100644
index 0000000000..06809732a4
--- /dev/null
+++ b/examples/usercmodule/cppexample/example.cpp
@@ -0,0 +1,17 @@
+extern "C" {
+#include <examplemodule.h>
+
+// Here we implement the function using C++ code, but since it's
+// declaration has to be compatible with C everything goes in extern "C" scope.
+mp_obj_t cppfunc(mp_obj_t a_obj, mp_obj_t b_obj) {
+    // Prove we have (at least) C++11 features.
+    const auto a = mp_obj_get_int(a_obj);
+    const auto b = mp_obj_get_int(b_obj);
+    const auto sum = [&]() {
+        return mp_obj_new_int(a + b);
+    } ();
+    // Prove we're being scanned for QSTRs.
+    mp_obj_t tup[] = {sum, MP_ROM_QSTR(MP_QSTR_hellocpp)};
+    return mp_obj_new_tuple(2, tup);
+}
+}
diff --git a/examples/usercmodule/cppexample/examplemodule.c b/examples/usercmodule/cppexample/examplemodule.c
new file mode 100644
index 0000000000..ceb588bef6
--- /dev/null
+++ b/examples/usercmodule/cppexample/examplemodule.c
@@ -0,0 +1,25 @@
+#include <examplemodule.h>
+
+// Define a Python reference to the function we'll make available.
+// See example.cpp for the definition.
+STATIC MP_DEFINE_CONST_FUN_OBJ_2(cppfunc_obj, cppfunc);
+
+// Define all properties of the module.
+// Table entries are key/value pairs of the attribute name (a string)
+// and the MicroPython object reference.
+// All identifiers and strings are written as MP_QSTR_xxx and will be
+// optimized to word-sized integers by the build system (interned strings).
+STATIC const mp_rom_map_elem_t cppexample_module_globals_table[] = {
+    { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_cppexample) },
+    { MP_ROM_QSTR(MP_QSTR_cppfunc), MP_ROM_PTR(&cppfunc_obj) },
+};
+STATIC MP_DEFINE_CONST_DICT(cppexample_module_globals, cppexample_module_globals_table);
+
+// Define module object.
+const mp_obj_module_t cppexample_user_cmodule = {
+    .base = { &mp_type_module },
+    .globals = (mp_obj_dict_t *)&cppexample_module_globals,
+};
+
+// Register the module to make it available in Python.
+MP_REGISTER_MODULE(MP_QSTR_cppexample, cppexample_user_cmodule, MODULE_CPPEXAMPLE_ENABLED);
diff --git a/examples/usercmodule/cppexample/examplemodule.h b/examples/usercmodule/cppexample/examplemodule.h
new file mode 100644
index 0000000000..d89384a630
--- /dev/null
+++ b/examples/usercmodule/cppexample/examplemodule.h
@@ -0,0 +1,5 @@
+// Include MicroPython API.
+#include "py/runtime.h"
+
+// Declare the function we'll make available in Python as cppexample.cppfunc().
+extern mp_obj_t cppfunc(mp_obj_t a_obj, mp_obj_t b_obj);
diff --git a/examples/usercmodule/cppexample/micropython.mk b/examples/usercmodule/cppexample/micropython.mk
new file mode 100644
index 0000000000..e10d965a00
--- /dev/null
+++ b/examples/usercmodule/cppexample/micropython.mk
@@ -0,0 +1,12 @@
+CPPEXAMPLE_MOD_DIR := $(USERMOD_DIR)
+
+# Add our source files to the respective variables.
+SRC_USERMOD += $(CPPEXAMPLE_MOD_DIR)/examplemodule.c
+SRC_USERMOD_CXX += $(CPPEXAMPLE_MOD_DIR)/example.cpp
+
+# Add our module directory to the include path.
+CFLAGS_USERMOD += -I$(CPPEXAMPLE_MOD_DIR)
+CXXFLAGS_USERMOD += -I$(CPPEXAMPLE_MOD_DIR)
+
+# We use C++ features so have to link against the standard library.
+LDFLAGS_USERMOD += -lstdc++