78 lines
2.9 KiB
Plaintext
78 lines
2.9 KiB
Plaintext
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This document describes the internals of the port for OpenRISC
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1000. The API is documented in or1k-support.h as Doxygen comments.
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# Data Structures
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+----------------+ 0x0
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| vectors |
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+----------------+
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| text,data,.. |
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+----------------+
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| bss |
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+----------------+
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| heap |
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| vv |
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| ^^ |
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| stack(s) |
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+----------------+ _or1k_board_mem_base +
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_or1k_board_mem_size
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## Stack and Heap
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The stack is allocated at the end of available physical memory which
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is defined by each board as _or1k_board_mem_base and
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_or1k_board_mem_size. The _or1k_stack_top and _or1k_stack_bottom are
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determined by those variables and _or1k_stack_size (which may be
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overwritten in _or1k_board_init_early).
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A second stack for exceptions is allocated as we allow exceptions to
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be arbitrary complex and call C functions etc. It is not an option to
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re-use the current software stack as we want to be so generic, that
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this can also be a virtual memory stack at moment of exception. The
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exception starts below the normal software stack and is
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_or1k_exception_stack_size large.
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Multicore: For each core a stack and exception stack is allocated and
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the stack pointer set at boot. That is: sp(core0) = _or1k_stack_top,
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sp(core1) = _or1k_stack_top - _or1k_stack_size, etc.
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## _or1k_stack_core (multicore only)
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An array of pointers to the software stacks (size:
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4*or1k_numcores()). It is dynamically allocated from heap in or1k_init
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by calling sbrk(). The pointers contain the values for stack top
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pointers as described above. This variable is essentially used on boot
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of the slave cores to configure the stack register.
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## _or1k_exception_stack_core (multicore only)
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An array of pointers to the exception stacks (size:
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4*or1k_numcores()). It is allocated identical as the stack_core
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array. It is loaded whenever an exception occurs to start with a clean
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stack in the exception.
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## _or1k_exception_handler_table
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A table of function pointers to the handlers of the exceptions. The
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generic exception handler checks if an exception handler is registered
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and calls it. There are 30 exceptions defined (0x0 is not an exception
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vector and 0x100 is reset which is static). This array resides in BSS
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and is therefore initialized as 0 (no handler registered) after start.
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Multicore: As the number of course is not known at compile time, the
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variable is a pointer to and array of arrays (cores x 30) which is
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allocated in or1k_init() on heap (using sbrk).
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## _or1k_interrupt_handler_table and _or1k_interrupt_handler_table_data_ptr
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The interrupt handlers are stored identical to to the exception handler table.
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## _or1k_reent
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The struct _or1k_reent contains formerly global data and allows for
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reentrancy. In the single core case, this is an allocated object,
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while it is a pointer to an array of structs in the multicore library.
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It is allocated in _or1k_reent_init() on the heap.
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