eCos Reference Manual
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# Default Synchronous Exception Handling

Most synchronous exception VSR table entries will point to a default exception VSR which is responsible for handling all exceptions in a generic manner. The default VSR simply saves the CPU state, makes any adjustments to the CPU state that is necessary, and calls `cyg_hal_exception_handler()`.

`cyg_hal_exception_handler()` needs to pass the exception on to some handling code. There are two basic destinations: enter GDB or pass the exception up to eCos. Exactly which destination is taken depends on the configuration. When the GDB stubs are included then the exception is passed to them, otherwise it is passed to eCos.

If an eCos application has been loaded by RedBoot then the VSR table entries will all point into RedBoot's exception VSR, and will therefore enter GDB if an exception occurs. If the eCos application wants to handle an exception itself, it needs to replace the the VSR table entry with one pointing to its own VSR. It can do this with the `HAL_VSR_SET_TO_ECOS_HANDLER()` macro.

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