66 lines
2.7 KiB
Plaintext
66 lines
2.7 KiB
Plaintext
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# Add a new board
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Before adding a new board, you may consider if your board can use another
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board definition and simply overwrite the weak symbols.
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If you think it is worth adding a new board, you need to perform the following
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steps:
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* Decide for a meaningful board name (refered to as <board> below). It should
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be specific enough (not openrisc..), but be rather generic if it may cover
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similar boards as well.
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* Create a file <board>.S (assembler) or <board>.c (C). Of course, C is easier
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to write and you can implement everything in C, but there are restrictions:
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* There is an early initialization function. It is called before the C
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library and even the stack are initialized. A default implementation skips
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this step, so everything will compile, but if you really need
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initialization that early you are bound to assembly language.
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* You essentially should not use the C library functions as this may lead to
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link issues and circular dependencies.
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You can copy board_tmpl.S or board_tmpl.c as starting point for your board.
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* The following symbols must be defined in your board file:
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* _or1k_board_mem_base: Memory base address
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* _or1k_board_mem_size: Memory size
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* _or1k_board_clk_freq: Clock frequency
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* _or1k_board_uart_base: UART base address. Set to 0 if no UART present.
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* _or1k_board_uart_baud: UART baud rate. Only used if UART base is > 0
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* _or1k_board_uart_IRQ: UART interrupt line. Only used if UART base is > 0
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You can define a weak attribute for all of the symbols so that they can
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be overwritten by the user (more flexibility).
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* The following functions need to be implemented:
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* _or1k_board_init: Is called after C library initialization and UART
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initialization.
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* _or1k_board_exit: Is called after the program has exited and the C library
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finished all deconstructions etc.
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Similar to the symbols you can define those functions weak.
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* The following functions can be implemented:
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* _or1k_board_init_early: Only in assembly (see above). Is called before
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anything is initialized, not even the stack! You can use all registers
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in this function. The default implementation in crt0.S skips this step,
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which is fine in most cases. If you decide to implement it, you need to
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define it with the global attribute to overwrite the default
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implementation. It is recommended to do so in assembler board files to
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keep the ability to overwrite the default implementation by the user.
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When you are done with your board, add it to libgloss/or1k/Makefile.in to the
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BOARDS variable and compile.
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