Documentation

Cross Compiling

LibOSDP is written in C and does not depend on any other libraries. You can compile it to practically any platform (including Windows). Follow the cross-compilation best practice for your platform. This document gives some ideas on how to do this but is not exhaustive. For the standard (non-cross) build, see Build and Install first.

Using CMake ​

LibOSDP can be compiled with a cross-compiler by passing a toolchain file to CMake via -DCMAKE_TOOLCHAIN_FILE=/path/to/toolchain-file.cmake.

If your toolchain is installed at /opt/toolchain/armv8l-linux-gnueabihf/ and the sysroot is at /opt/toolchain/armv8l-linux-gnueabihf/sysroot, the toolchain-file.cmake should look like this:

set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR arm)

# specify the cross compiler and sysroot
set(TOOLCHAIN_INST_PATH /opt/toolchain/armv8l-linux-gnueabihf)
set(CMAKE_C_COMPILER    ${TOOLCHAIN_INST_PATH}/bin/armv8l-linux-gnueabihf-gcc)
set(CMAKE_CXX_COMPILER  ${TOOLCHAIN_INST_PATH}/bin/armv8l-linux-gnueabihf-g++)
set(CMAKE_SYSROOT       ${TOOLCHAIN_INST_PATH}/sysroot)

# don't search for programs in the build host directories
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)

# search for libraries and headers in the target directories only
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)

Place the toolchain file in a common path (such as where the toolchain is installed) and reference it from your build directory:

mkdir build && cd build
cmake -DCMAKE_TOOLCHAIN_FILE=/opt/toolchain/armv8l-linux-gnueabihf/toolchain-file.cmake ..
make

Using Make ​

Use the --cross-compile flag in configure.sh and then invoke make:

./configure.sh --cross-compile arm-none-
make
make DESTDIR=/opt/arm-none-sysroot/ install

Porting to a New Platform ​

LibOSDP itself is portable C, but it relies on a small set of platform primitives supplied by its utils/ submodule (c-utils). On mainstream targets (Linux, macOS, Windows) and the built-in platforms (Arduino, Zephyr, Mynewt) these are provided automatically. For an unrecognized or bare-metal target, you provide them yourself:

  • Entropy — rand_u32(). This backs the secure channel nonces, so it must be a cryptographically strong source (see Random Number Generation). The default is __weak, so you can override it with your MCU's hardware TRNG. On unknown bare-metal targets the symbol is left undefined on purpose, so a missing entropy source becomes a link error rather than a silent weak PRNG.
  • Time — a monotonic clock (gettimeofday() / usec_now() / millis_now()), used for OSDP's protocol timing. Wire this to your platform's tick source.
  • Logging — an output hook (a puts-style function) passed to the logger, plus a working printf from your C runtime.
  • Endianness — auto-detected in utils/byteorder.h; configure it if your target is not recognized.

The declarations and platform-detection macros live in utils/include/utils/utils.h; the reference implementations you extend or override are in utils/src/utils.c.