[ECOS] Question about fixed vector table(ARM).

Mark Salter msalter@redhat.com
Thu May 16 05:00:00 GMT 2002


>>>>> HuangQiang  writes:

> Thank you very much. I still have one question about the fixed vector table.
> In ARM vectors.s file takes care of the vector table(from 0x00) setup and
> fixed vector table(from 0x20) setup. While branch to the vector it first
> branch to the vector table(from 0x00) and then directed to fixed vector
> table(from 0x20) then to the actual services routine. Why this fixed vector
> table is needed here? Can't we just setup the vector table (from 0x00) and
> branch to the services routine indirection of fixed vector table?

A branch instruction has only a 24-bit range, so you would not
have access to the full address range if you used a branch in
the CPU vector table. We use the table at 0x20 to hold full 32-bit
addresses of the service routines. The instructions in the CPU
vector table simply load those 32-bit values to the PC register.

--Mark

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