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README.md

Introduction

These directories provide the porting layer that allows the high level C APIs to be built and run on a supported MCU.

No attempt is made to create a full MCU porting API; only the APIs necessary to run the high level C APIs are implemented here.

Note: aside from calling uPortInit() at start of day, uPortDeinit() at end of day, and uPortFree() if you are freeing some memory that ubxlib has allocated, this API is NOT INTENDED FOR CUSTOMER USE. You may use it if you wish but it is quite restricted and is intended only to provide what ubxlib needs in the form that ubxlib needs it, internally to the ubxlib code. It is used in the ubxlib examples but that is only because we need those examples to work on all of our supported platforms. When writing your application you are better off using the fully-featured native APIs of your platform.

Usage

The api directory defines the port API, each API function documented in the header file. The clib directory contains implementations of C library APIs that may be missing on some platforms (e.g. strtok_r, the re-entrant version of the strtok library function). In the platform directory you will find the implementation of the porting API on various target SDKs and MCUs and the necessary instructions to create a working binary and tests on each of those target MCUs. Please refer to the README.md files in your chosen target platform directory for more information.

The test directory contains tests for this API that can be run on any platform.

DIY

If your platform is not currently supported you may be able to port it yourself, something like this:

  • provide implementations of the functions in the port api; use the existing platform implementations for guidance (e.g. platform/nrf5sdk/src):
    • the initialisation and OS interfaces are probably the simplest: you will need task creation/deletion and an entry point into task-land, plain-old non-recursive mutexes, a way to queue things, a way to block a task for x milliseconds, a way to obtain a count of [32-bit] milliseconds since boot and also semaphores,
    • the common platform/common/event_queue code will likely form most of your implementation of the u_port_event_queue.h API,
    • you will need a way to get debug strings off the platform, i.e. [non-floating point] printf() to somewhere,
    • the GPIO API will require some plumbing into the specifics of your MCU,
    • the UART API will likely be the most complex thing to implement; you will probably need to know details of the interrupt and DMA behaviours of your MCU to complete this,
    • if you intend to use a GNSS chip connected directly to your MCU via I2C then you will need to port the I2C API,
    • if you intend to use a GNSS chip connected directly to your MCU through SPI then you will need to port the SPI API,
    • if you intend to use the BLE that is on-chip, inside the same host MCU as ubxlib is running, you will require an implementation of the GATT access functions,
    • if your platform does not use newlib (if you are using GCC it will bring newlib with it) then you may find you are missing some C library functions; implementations of C library functions we have already found to be missing on some platforms can be found in port/clib and can just be hooked-in from there but you may need to add more if your code doesn't compile,
    • if your platform does not offer malloc() and free(), or you wish to do your own thing with heap memory, you should override the default, weakly-linked, implementations of pUPortMalloc() and uPortFree() by defining your own implementations of these functions in a file inside the src directory of your port,
    • if your platform supports setting a time-zone offset you will need to implement uPortGetTimezoneOffsetSeconds(); if not then you may simply include the file port/u_port_timezone.c in your build (already included through weak linkage via ubxlib.cmake and ubxlib.mk) to get a default timezone offset of zero,
    • if your platform has some form of compile-time device configuration mechanism of its own (like the Zephyr Device Tree) then you may wish to implement uPortBoardCfgDevice() and uPortBoardCfgNetwork() (see port/api/u_port_board_cfg.h) to accommodate that.
  • provide your own versions of the header files u_cfg_app_platform_specific.h, u_cfg_hw_platform_specific.h, u_cfg_test_platform_specific.h and u_cfg_os_platform_specific.h (see examples in the existing platform directories); take particular note of translating the task priority values into those of your OS,
  • provide your own build metadata files (for CMake, Make, a home-grown Python lash-up, whatever): usually your chosen platform will dictate the shape of these and you just need to add to your existing structure the paths to the ubxlib source files and the ubxlib include files; otherwise take a look at the existing nrf5 GCC platform or static_size platforms as a starting point (though note that the latter does not bring in any platform or test files),
  • add Unity to your build and then compile and run the tests in u_port_test.c: if these pass then you have likely completed the necessary porting.

Shared CMake file

For ports that use CMake ubxlib.cmake can be used to collect the ubxlib non-platform-specific source code files, include directories etc.

ubxlib.cmake is typically included in a port specific CMake file and will then define a couple of variables that the calling CMake file can make use of (see the esp32 component CMakeLists.txt as example).

Before including ubxlib.cmake you must set the variable UBXLIB_BASE to root directory of ubxlib.

You must also specify what ubxlib features to enable using the UBXLIB_FEATURES variable described below.

To bring the platform-specific files into your CMake file, take a look at, for instance, the Windows-platform CMakeLists.txt file.

UBXLIB_FEATURES

Available features are:

  • u_lib: include the lib_common API,
  • short_range: include wifi, ble and short_range API,
  • short_range_gen2: should be used IN ADDITION TO short_range and ONLY IF you are using the short-range NORA-W36 module; this is required since NORA-W36 comes with a second generation u-connectExpress,
  • cell: include cell API,
  • gnss: include gnss API,
  • geodesic: include GeographicLib, required only if U_CFG_GEOFENCE is defined and shapes larger than 1 km in size are being used in the fence, see u_geofence_geodesic.h for details.

Example

set(UBXLIB_BASE <path_to_ubxlib>)
# Set the ubxlib features to compile (all needs to be enabled at the moment)
set(UBXLIB_FEATURES short_range cell gnss)

# From this line we will get back:
# - UBXLIB_SRC
# - UBXLIB_INC
# - UBXLIB_PRIVATE_INC
# - UBXLIB_TEST_SRC
# - UBXLIB_TEST_INC
# and optionally:
# - UBXLIB_EXTRA_LIBS
# - UBXLIB_COMPILE_OPTIONS
include(${UBXLIB_BASE}/port/ubxlib.cmake)

Output Variables

After ubxlib.cmake has been included the following variables will be available:

  • UBXLIB_SRC: A list of all the non-platform-specific .c files,
  • UBXLIB_INC: A list of the public include directories,
  • UBXLIB_PRIVATE_INC: A list of the private include directories required to build ubxlib,
  • UBXLIB_TEST_SRC: A list of all the test .c files,
  • UBXLIB_TEST_INC: A list of test include directories,

Shared Makefile

For ports that use make ubxlib.mk can be used to collect the non-platform-specific ubxlib source code files, include directories etc. in the same way as for CMake above.

Just like the shared CMake file you must first set the variable UBXLIB_BASE to root directory of ubxlib and configure the ubxlib features using UBXLIB_FEATURES (see above). ubxlib.mk will then define the same output variables as the shared CMake above (see Output Variables)

To bring the platform-specific files into your Makefile, take a look at, for instance, the STM32F4 Makefile.

Example

# Include ubxlib src and inc
UBXLIB_BASE = <path_to_ubxlib>
UBXLIB_FEATURES = cell gnss short_range
# From this line we will get back:
# - UBXLIB_SRC
# - UBXLIB_INC
# - UBXLIB_PRIVATE_INC
# - UBXLIB_TEST_SRC
# - UBXLIB_TEST_INC
# and optionally:
# - UBXLIB_EXTRA_LIBS
# - UBXLIB_COMPILE_OPTIONS
include $(UBXLIB_BASE)/port/ubxlib.mk