Project structure

Build system

The XMOS USB Audio Reference Design software and associated libraries employ the XCommon CMake build system. The XCommon CMake build system uses CMake to configure and generate the build environment which can then be built using xmake. As part of configuring the build environment, if there are any missing dependencies, XCommon CMake fetches them using git.

Note

All required dependencies are included in the sw_usb_audio zip download.

Applications and libraries

The sw_usb_audio GIT repository includes multiple application directories. Each application directory contains a CMakeLists.txt file which describes the build configs for that application. The format of the CMakeLists.txt is described here XCommon CMake uses the CMakeLists.txt to generate Makefiles that can be compiled using xmake into executables. Typically, there’s one application directory per hardware platform. Applications and their respective hardware platforms are listed in Table 1.

Table 1 USB Audio Reference Applications

Application	Hardware platform
app_usb_aud_xk_316_mc	xcore.ai USB Audio 2.0 Multi-channel Audio Board
app_usb_aud_xk_216_mc	xcore-200 USB Audio 2.0 Multi-channel Audio Board
app_usb_aud_xk_evk_xu316	xcore.ai Evaluation Kit

The applications depend on several modules (or libraries), each of which have their own GIT repository. The immediate dependency libraries for the applications are specified by setting the APP_DEPENDENT_MODULES variable in the deps.cmake file. deps.cmake lists the common dependencies for all the applications and is included in each application’s CMakeLists.txt.

The dependency list specified in the deps.cmake can be extended to add new dependencies. Refer to the XCommon CMake Dependency Format documentation for more information about adding dependencies.

A shared file containing common dependencies ensures a consistent set of dependencies between all of the applications.

Each library has a lib_build_info.cmake which lists the library source, compile flags and dependencies. The library dependencies are specified in the LIB_DEPENDENT_MODULES variable in the lib_build_info.cmake. This allows dependency trees and nesting. XCommon CMake builds up a tree which is traversed depth-first, and populates the sandbox, fetching any missing dependencies by cloning them from github.

Most of the core code is contained in the XMOS USB Audio Library (lib_xua). A full list of core dependencies is shown in Table 2.

Table 2 Core dependencies of USB Audio

Library	Description
lib_xua	Common code for USB audio applications
lib_xud	Low level USB device library
lib_spdif	S/PDIF transmit and receive code
lib_adat	ADAT transmit and receive code
lib_mic_array	PDM microphone interface and decimator
lib_xassert	Lightweight assertions library

Note

Some of these core dependencies will have their own dependencies, for example lib_mic_array depnds on lib_xassert (see above), lib_logging (a lightweight print library) and lib_xcore_math (a DSP library).