[Libre-soc-bugs] [Bug 238] POWER Compressed Formal Standard writeup

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=238

--- Comment #140 from Alexandre Oliva <oliva at gnu.org> ---
luke, please don't feel pressured to answer right away.  take some rest first,
then read it.  we're clearly miscommunicating, and your being at the end of
your day probably contributes to that.

> N does not exist in 10bit mode

irrelevant, that's a 16-bit only encoding, not available in 10-bit insns

> however for 16 bit mode N *can* have meaning, giving 4 encoding possibilities

point is N has only been assigned meanings when bit 15 holds M

this is not the case of the extsb insn I quoted:

| N | 1 |  RT | | 100.0 | RB  | 0 0 0 | 0 | extsb

see the N there at bit 0?  I do.

see M there at bit 15?  I don't.  I see that fixed at 0.

nothing was specified as to the meaning of N in an insn that doesn't have an M
at bit 15.

is that zero at bit 15 supposed to be an M?  better write M instead of 0 if so,
as elsewhere.

or is that fixed as zero, as a sub-opcode, but it's regardless supposed to be
interpreted as an M when combined with N?  if so, better write M=0

or is that N a don't care?  if so, better write that down, instead of naming it
N, because N without M is meaningless AFAICT

or does that N without M mean something else, that has so far not been
specified?

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