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| -rw-r--r-- | bsp-howto/initilization_code.rst | 152 |
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diff --git a/bsp-howto/initilization_code.rst b/bsp-howto/initilization_code.rst index 271d2d8..30c7537 100644 --- a/bsp-howto/initilization_code.rst +++ b/bsp-howto/initilization_code.rst @@ -52,22 +52,6 @@ functionality. In most BSPs, the directory named ``start340`` in the gen68340 BSP would be simply named ``start`` or start followed by a BSP designation. -Required Global Variables -========================= - -Although not strictly part of initialization, there are a few global variables -assumed to exist by reusable device drivers. These global variables should -only defined by the BSP when using one of these device drivers. - -The BSP author probably should be aware of the ``Configuration`` Table -structure generated by ``<rtems/confdefs.h>`` during debug but should not -explicitly reference it in the source code. There are helper routines provided -by RTEMS to access individual fields. - -In older RTEMS versions, the BSP included a number of required global -variables. We have made every attempt to eliminate these in the interest of -simplicity. - Board Initialization ==================== @@ -183,139 +167,3 @@ semaphores. After completing execution, this routine returns to the ``boot_card()`` routine. In case of errors, the initialization should be terminated via ``bsp_fatal()``. - -Device Driver Initialization ----------------------------- - -At this point in the initialization sequence, the initialization routines for -all of the device drivers specified in the Device Driver Table are invoked. -The initialization routines are invoked in the order they appear in the Device -Driver Table. - -The Driver Address Table is part of the RTEMS Configuration Table. It defines -device drivers entry points (initialization, open, close, read, write, and -control). For more information about this table, please refer to the -*Configuring a System* chapter in the *RTEMS Application C User's Guide*. - -The RTEMS initialization procedure calls the initialization function for every -driver defined in the RTEMS Configuration Table (this allows one to include -only the drivers needed by the application). - -All these primitives have a major and a minor number as arguments: - -- the major number refers to the driver type, - -- the minor number is used to control two peripherals with the same driver (for - instance, we define only one major number for the serial driver, but two - minor numbers for channel A and B if there are two channels in the UART). - -The Interrupt Vector Table -========================== - -The Interrupt Vector Table is called different things on different processor -families but the basic functionality is the same. Each entry in the Table -corresponds to the handler routine for a particular interrupt source. When an -interrupt from that source occurs, the specified handler routine is invoked. -Some context information is saved by the processor automatically when this -happens. RTEMS saves enough context information so that an interrupt service -routine can be implemented in a high level language. - -On some processors, the Interrupt Vector Table is at a fixed address. If this -address is in RAM, then usually the BSP only has to initialize it to contain -pointers to default handlers. If the table is in ROM, then the application -developer will have to take special steps to fill in the table. - -If the base address of the Interrupt Vector Table can be dynamically changed to -an arbitrary address, then the RTEMS port to that processor family will usually -allocate its own table and install it. For example, on some members of the -Motorola MC68xxx family, the Vector Base Register (``vbr``) contains this base -address. - -Interrupt Vector Table on the gen68340 BSP ------------------------------------------- - -The gen68340 BSP provides a default Interrupt Vector Table in the file -``$BSP_ROOT/start340/start340.s``. After the ``entry`` label is the definition -of space reserved for the table of interrupts vectors. This space is assigned -the symbolic name of ``__uhoh`` in the ``gen68340`` BSP. - -At ``__uhoh`` label is the default interrupt handler routine. This routine is -only called when an unexpected interrupts is raised. One can add their own -routine there (in that case there's a call to a routine - -$BSP_ROOT/startup/dumpanic.c - that prints which address caused the interrupt -and the contents of the registers, stack, etc.), but this should not return. - -Chip Select Initialization -========================== - -When the microprocessor accesses a memory area, address decoding is handled by -an address decoder, so that the microprocessor knows which memory chip(s) to -access. The following figure illustrates this: - -.. code-block:: c - - +-------------------+ - ------------| | - ------------| |------------ - ------------| Address |------------ - ------------| Decoder |------------ - ------------| |------------ - ------------| | - +-------------------+ - CPU Bus Chip Select - -The Chip Select registers must be programmed such that they match the -``linkcmds`` settings. In the gen68340 BSP, ROM and RAM addresses can be found -in both the ``linkcmds`` and initialization code, but this is not a great way -to do this. It is better to define addresses in the linker script. - -Integrated Processor Registers Initialization -============================================= - -The CPUs used in many embedded systems are highly complex devices with multiple -peripherals on the CPU itself. For these devices, there are always some -specific integrated processor registers that must be initialized. Refer to the -processors' manuals for details on these registers and be VERY careful -programming them. - -Data Section Recopy -=================== - -The next initialization part can be found in -``$BSP340_ROOT/start340/init68340.c``. First the Interrupt Vector Table is -copied into RAM, then the data section recopy is initiated -(``_CopyDataClearBSSAndStart`` in ``$BSP340_ROOT/start340/startfor340only.s``). - -This code performs the following actions: - -- copies the .data section from ROM to its location reserved in RAM (see - :ref:`Initialized Data` for more details about this copy), - -- clear ``.bss`` section (all the non-initialized data will take value 0). - -The RTEMS Configuration Table -============================= - -The RTEMS configuration table contains the maximum number of objects RTEMS can -handle during the application (e.g. maximum number of tasks, semaphores, -etc.). It's used to allocate the size for the RTEMS inner data structures. - -The RTEMS configuration table is application dependent, which means that one -has to provide one per application. It is usually defined by defining macros -and including the header file ``<rtems/confdefs.h>``. In simple applications -such as the tests provided with RTEMS, it is commonly found in the main module -of the application. For more complex applications, it may be in a file by -itself. - -The header file ``<rtems/confdefs.h>`` defines a constant table named -``Configuration``. With RTEMS 4.8 and older, it was accepted practice for the -BSP to copy this table into a modifiable copy named ``BSP_Configuration``. -This copy of the table was modified to define the base address of the RTEMS -Executive Workspace as well as to reflect any BSP and device driver -requirements not automatically handled by the application. In 4.9 and newer, -we have eliminated the BSP copies of the configuration tables and are making -efforts to make the configuration information generated by -``<rtems/confdefs.h>`` constant and read only. - -For more information on the RTEMS Configuration Table, refer to the *RTEMS -Application C User's Guide*. |