splits write.c, adds iss implementation and adds CMake build system

CMakeLists.txt

@@ -1,11 +1,28 @@
-cmake_minimum_required(VERSION 3.12)
-project(bsp C)
+cmake_minimum_required(VERSION 3.21)
+project(mnrs-bsp LANGUAGES ASM C)
+
+if(NOT DEFINED BOARD)
+message(FATAL_ERROR "No Board selected")
+endif()
+add_compile_definitions("BOARD_${BOARD}")
+# check if we are building for a testbench, adjust the Base accordingly
+set(BOARD_BASE ${BOARD})
+
+option(SEMIHOSTING "Enable semihosting support" OFF)
+if(SEMIHOSTING)
+    add_compile_definitions(SEMIHOSTING)
+endif()
+
+add_library(startup STATIC env/start.S env/entry.S)
+target_include_directories(startup PUBLIC env include)
+
 add_subdirectory(libwrap)
-add_subdirectory(env)
-message(STATUS " in bsp with ${CMAKE_CXX_FLAGS}")
-message(STATUS " SUPPORTED_BOARDS= ${SUPPORTED_BOARDS}")
-add_library(${PROJECT_NAME} INTERFACE)
-target_include_directories(${PROJECT_NAME} INTERFACE 
-include/
-env/${BOARD}
-env/)
+
+add_library(bsp INTERFACE)
+target_link_libraries(bsp INTERFACE startup wrap)
+target_include_directories(bsp INTERFACE env/${BOARD_BASE})
+target_link_options(bsp INTERFACE LINKER:--no-warn-rwx-segments -nostartfiles -T ${CMAKE_CURRENT_SOURCE_DIR}/env/${BOARD_BASE}/link.lds)
+if(SEMIHOSTING)
+    target_include_directories(bsp INTERFACE /include)
+    target_sources(bsp INTERFACE env/semihosting.c env/trap.c)
+endif()