Comtrol eCos - Manual (Page 346)

Chapter 11. Porting Guide
• Write hal_interrupt_stack_call_pending_dsrs() . If this function is defined in hal_arch.h then it
should appear here. The purpose of this function is to call DSRs on the interrupt stack rather than the current
thread’s stack. This is not an essential feature, and may be left until later. However it interacts with the stack
switching that goes on in the interrupt VSR, so it may make sense to write these pieces of code at the same
time to ensure consistency.
When this function is implemented it should do the following:
• Take a copy of the current SP and then switch to the interrupt stack.
• Save the old SP, together with the CPU status register (or whatever register contains the interrupt enable
status) and any other registers that may be corrupted by a function call (such as any link register) to
locations in the interrupt stack.
• Enable interrupts.
• Call cyg_interrupt_call_pending_DSRs() . This is a kernel functions that actually calls any pending
DSRs.
• Retrieve saved registers from the interrupt stack and switch back to the current thread stack.
• Merge the interrupt enable state recorded in the save CPU status register with the current value of the sta-
tus register to restore the previous enable state. If the status register does not contain any other persistent
state then this can be a simple restore of the register. However if the register contains other state bits that
might have been changed by a DSR, then care must be taken not to disturb these.
• Define any data items needed. Typically vectors.S may contain definitions for the VSR table, the interrupt
tables and the interrupt stack. Sometimes these are only default definitions that may be overridden by the
variant or platform HALs.
7. Write context.S . This file contains the context switch code. See the Section called Thread Context Switching
in Chapter 9 for details of how these functions operate. This file may also contain the implementation of
hal_setjmp() and hal_longjmp() .
8. Write hal_misc.c . This file contains any C data and functions needed by the HAL. These might include:
• hal_interrupt_*[] . In some HALs, if these arrays are not defined in vectors.S then they must be
defined here.
• cyg_hal_exception_handler() . This function is called from the exception VSR. It usually does extra
decoding of the exception and invokes any special handlers for things like FPU traps, bus errors or memory
exceptions. If there is nothing special to be done for an exception, then it either calls into the GDB stubs, by
calling
__handle_exception() , or invokes the kernel by calling cyg_hal_deliver_exception() .
• hal_arch_default_isr() . The hal_interrupt_handlers[] array is usually initialized with pointers
to hal_default_isr() , which is defined in the common HAL. This function handles things like Ctrl-C
processing, but if that is not relevant, then it will call hal_arch_default_isr() . Normally this function
should just return zero.
• cyg_hal_invoke_constructors() . This calls the constructors for all static objects before the program
starts. eCos relies on these being called in the correct order for it to function correctly. The exact way
in which constructors are handled may differ between architectures, although most use a simple table of
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