From 72a62ad88f82fe1ffee50024db4dd0f3fa5806f7 Mon Sep 17 00:00:00 2001 From: Chris Johns Date: Thu, 3 Nov 2016 16:58:08 +1100 Subject: Rename all manuals with an _ to have a -. It helps released naming of files. --- bsp-howto/target_dependant_files.rst | 229 +++++++++++++++++++++++++++++++++++ 1 file changed, 229 insertions(+) create mode 100644 bsp-howto/target_dependant_files.rst (limited to 'bsp-howto/target_dependant_files.rst') diff --git a/bsp-howto/target_dependant_files.rst b/bsp-howto/target_dependant_files.rst new file mode 100644 index 0000000..ecc9b3a --- /dev/null +++ b/bsp-howto/target_dependant_files.rst @@ -0,0 +1,229 @@ +.. comment SPDX-License-Identifier: CC-BY-SA-4.0 + +.. COMMENT: COPYRIGHT (c) 1988-2008. +.. COMMENT: On-Line Applications Research Corporation (OAR). +.. COMMENT: All rights reserved. + + +Target Dependent Files +###################### + +RTEMS has a multi-layered approach to portability. This is done to maximize the +amount of software that can be reused. Much of the RTEMS source code can be +reused on all RTEMS platforms. Other parts of the executive are specific to +hardware in some sense. RTEMS classifies target dependent code based upon its +dependencies into one of the following categories. + +- CPU dependent + +- Board dependent + +- Peripheral dependent + +CPU Dependent +============= + +This class of code includes the foundation routines for the executive proper +such as the context switch and the interrupt subroutine implementations. +Sources for the supported processor families can be found in +``cpukit/score/cpu``. A good starting point for a new family of processors is +the ``no_cpu`` directory, which holds both prototypes and descriptions of each +needed CPU dependent function. + +CPU dependent code is further subcategorized if the implementation is dependent +on a particular CPU model. For example, the MC68000 and MC68020 processors are +both members of the m68k CPU family but there are significant differences +between these CPU models which RTEMS must take into account. + +The source code found in the ``cpukit/score/cpu`` is required to only depend +upon the CPU model variations that GCC distinguishes for the purposes of +multilib'ing. Multilib is the term the GNU community uses to refer to building +a single library source multiple times with different compiler options so the +binary code generated is compatible. As an example, from GCC's perspective, +many PowerPC CPU models are just a PPC603e. Remember that GCC only cares about +the CPU code itself and need not be aware of any peripherals. In the embedded +community, we are exposed to thousands of CPU models which are all based upon +only a relative small number of CPU cores. + +Similarly for the SPARC/ERC32 BSP, the ``RTEMS_CPU`` is specified as ``erc32`` +which is the name of the CPU model and BSP for this SPARC V7 system on chip. +But the multilib variant used is actually ``v7`` which indicates the ERC32 CPU +core is a SPARC V7. + +Board Dependent +=============== + +This class of code provides the most specific glue between RTEMS and a +particular board. This code is represented by the Board Support Packages and +associated Device Drivers. Sources for the BSPs included in the RTEMS +distribution are located in the directory ``c/src/lib/libbsp``. The BSP source +directory is further subdivided based on the CPU family and BSP. + +Some BSPs may support multiple board models within a single board family. This +is necessary when the board supports multiple variants on a single base board. +For example, the Motorola MVME162 board family has a fairly large number of +variations based upon the particular CPU model and the peripherals actually +placed on the board. + +Peripheral Dependent +==================== + +This class of code provides a reusable library of peripheral device drivers +which can be tailored easily to a particular board. The libchip library is a +collection of reusable software objects that correspond to standard +controllers. Just as the hardware engineer chooses a standard controller when +designing a board, the goal of this library is to let the software engineer do +the same thing. + +The source code for the reusable peripheral driver library may be found in the +directory ``c/src/lib/libchip``. The source code is further divided based upon +the class of hardware. Example classes include serial communications +controllers, real-time clocks, non-volatile memory, and network controllers. + +Questions to Ask +================ + +When evaluating what is required to support RTEMS applications on a particular +target board, the following questions should be asked: + +- Does a BSP for this board exist? + +- Does a BSP for a similar board exists? + +- Is the board's CPU supported? + +If there is already a BSP for the board, then things may already be ready to +start developing application software. All that remains is to verify that the +existing BSP provides device drivers for all the peripherals on the board that +the application will be using. For example, the application in question may +require that the board's Ethernet controller be used and the existing BSP may +not support this. + +If the BSP does not exist and the board's CPU model is supported, then examine +the reusable chip library and existing BSPs for a close match. Other BSPs and +libchip provide starting points for the development of a new BSP. It is often +possible to copy existing components in the reusable chip library or device +drivers from BSPs from different CPU families as the starting point for a new +device driver. This will help reduce the development effort required. + +If the board's CPU family is supported but the particular CPU model on that +board is not, then the RTEMS port to that CPU family will have to be augmented. +After this is done, development of the new BSP can proceed. + +Otherwise both CPU dependent code and the BSP will have to be written. + +This type of development often requires specialized skills and there are people +in the community who provide those services. If you need help in making these +modifications to RTEMS try a search in a search engine with something like +"rtems support". The RTEMS Project encourages users to use support services +however we do not endorse any providers. + +CPU Dependent Executive Files +============================= + +The CPU dependent files in the RTEMS executive source code are found in the +following directory: + +.. code-block:: c + + cpukit/score/cpu/ + +where is replaced with the CPU family name. + +Within each CPU dependent directory inside the executive proper is a file named +``.h`` which contains information about each of the supported CPU models +within that family. + +CPU Dependent Support Files +=========================== + +The CPU dependent support files contain routines which aid in the development +of applications using that CPU family. For example, the support routines +may contain standard trap handlers for alignment or floating point exceptions +or device drivers for peripheral controllers found on the CPU itself. +This class of code may be found in the following directory: + +.. code-block:: c + + c/src/lib/libcpu/ + +CPU model dependent support code is found in the following directory: + +.. code-block:: c + + c/src/lib/libcpu// + + may be a specific CPU model name or a name indicating a CPU core or +a set of related CPU models. The file ``configure.ac`` in each +``c/src/lib/libcpu/`` directory contains the logic which enables the +appropriate subdirectories for the specific CPU model your BSP has. + +Board Support Package Structure +=============================== + +The BSPs are all under the ``c/src/lib/libbsp`` directory. Below this +directory, there is a subdirectory for each CPU family. Each BSP is found +under the subdirectory for the appropriate processor family (arm, powerpc, +sparc, etc.). In addition, there is source code available which may be shared +across all BSPs regardless of the CPU family or just across BSPs within a +single CPU family. This results in a BSP using the following directories: + +.. code-block:: c + + c/src/lib/libbsp/shared + c/src/lib/libbsp//shared + c/src/lib/libbsp// + +Under each BSP specific directory, there is a collection of subdirectories. +For commonly provided functionality, the BSPs follow a convention on +subdirectory naming. The following list describes the commonly found +subdirectories under each BSP. + +- ``console``: + is technically the serial driver for the BSP rather than just a console + driver, it deals with the board UARTs (i.e. serial devices). + +- ``clock``: + support for the clock tick - a regular time basis to the kernel. + +- ``timer``: + support of timer devices. + +- ``rtc`` or ``tod``: + support for the hardware real-time clock. + +- ``nvmem``: + support for non-volatile memory such as EEPROM or Flash. + +- ``network``: + the Ethernet driver. + +- ``shmsupp``: + support of shared memory driver MPCI layer in a multiprocessor system, + +- ``include``: + include files for this BSP. + +- ``gnatsupp``: + BSP specific support for the GNU Ada run-time. Each BSP that wishes to have + the possibility to map faults or exceptions into Ada language exceptions or + hardware interrupts into Ada interrupt tasks must provide this support. + +There may be other directories in the BSP tree and the name should be +indicative of the functionality of the code within that directory. + +The build order of the BSP is determined by the Makefile structure. This +structure is discussed in more detail in the :ref:`Makefiles` chapter. + +.. sidebar: + +This manual refers to the gen68340 BSP for numerous concrete examples. You +should have a copy of the gen68340 BSP available while reading this piece of +documentation. This BSP is located in the following directory: + +.. code-block:: c + + c/src/lib/libbsp/m68k/gen68340 + +Later in this document, the $BSP340_ROOT label will be used to refer to this +directory. -- cgit v1.2.3