Add Hello_World example

examples/hello_world/CMakeLists.txt

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+# For more information about build system see
+# https://docs.espressif.com/projects/esp-idf/en/latest/api-guides/build-system.html
+# The following five lines of boilerplate have to be in your project's
+# CMakeLists in this exact order for cmake to work correctly
+cmake_minimum_required(VERSION 3.5)
+
+set(EXTRA_COMPONENT_DIRS "/home/max/net/esp32-gnat-rts/")
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(hello_world)
+

examples/hello_world/main/CMakeLists.txt

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+idf_component_register(SRCS "hello_world.c"
+                    INCLUDE_DIRS "."
+                    REQUIRES esp32-gnat-rts)
+
+# Build *.gpr into a static library
+add_custom_command(OUTPUT ${BUILD_DIR}/libadamain.a
+     COMMAND gprbuild -b -c -p -P ${COMPONENT_DIR}/hello_world.gpr
+               --db ${COMPONENT_DIR}/gprconfig
+               --autoconf=${BUILD_DIR}/config.cgpr
+               --RTS=${BUILD_DIR}/rts
+          && xtensa-esp32-elf-ar rcs ${BUILD_DIR}/libadamain.a
+               ${COMPONENT_DIR}/.objs/b__hello_world.o
+               ${COMPONENT_DIR}/.objs/hello_world.o
+     DEPENDS hello_world.gpr hello_world.adb
+     VERBATIM)
+
+add_custom_target(adamain DEPENDS ${BUILD_DIR}/libadamain.a)
+add_dependencies(${COMPONENT_LIB} adamain)
+target_link_libraries(${COMPONENT_LIB} ${BUILD_DIR}/libadamain.a)
+

examples/hello_world/main/hello_world.adb

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+with System;
+
+procedure Hello_World is
+
+   procedure puts
+     (data : System.Address)
+      with Import, Convention => C, External_Name => "puts";
+
+   Hello : String := "Hello from Ada!" & ASCII.NUL;
+begin
+  puts (Hello'Address);
+end;

examples/hello_world/main/hello_world.c

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+extern void main();
+
+void app_main(void)
+{
+  main();
+}

examples/hello_world/main/hello_world.gpr

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+project Hello_World is
+   for Target use "xtensa-esp32-elf";
+   for Main use ("hello_world.adb");
+   for Object_Dir use ".objs";
+end Hello_World;