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Re: opcode bits beyond base-insn-bitsize
- From: DJ Delorie <dj at redhat dot com>
- To: dje at sebabeach dot org
- Cc: geoffk at geoffk dot com, cgen at sources dot redhat dot com
- Date: Tue, 24 Dec 2002 12:52:59 -0500
- Subject: Re: opcode bits beyond base-insn-bitsize
- References: <20021224055735.2F216B539@seba.sebabeach.org>
> Can anyone remember what the details are?
> i.e. what didn't work? assembler? disassembler? simulator?
xstormy16 has both 16bit and 32bit opcodes, and some of the 32bit
opcodes have decodable bits in the second half. The base-insn-bitsize
is used to set up the masks and such, so it needs to be at least as
big as the largest decodable bits.
The tricky bit is when the 32-bit opcodes are mixed endian (i.e. the
first 16 bits are swapped independently of the second 16 bits,
resulting in ABCD or BADC endian, but not DCBA).