[Libre-soc-bugs] [Bug 741] bitmanip ALU implementation

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Fri Nov 12 05:13:24 GMT 2021


--- Comment #13 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #12)
> (In reply to Jacob Lifshay from comment #11)
> > Note that the form I added is called TI (for TernaryI) and the immediate
> > field is called TII (for TernaryI Immediate).
> the convention, created by the microwatt team, and followed in all 75
> operations, is to use the same microcode op for both immediate and
> nonimmediate.
> this is achieved by placing the immediate into the data lanes of the
> registers
> whereupon the Function Unit knows nothing at all about immediates and 
> consequently a designation and naming convention based on immediates
> is completely inappropriate and misleading.

here, the name is based on immediate (or not) because the TI form is *only*
ever used with ternaryi...ternary will instead be a separate form MR4 (Modified
4-register -- exact name TBD) with RT, RA, RB, RC, and *no* immediate. This is
independent of whatever OP_TERNARY/OP_TERNARYI name we decide to use.

we can switch to merging both ternary and ternaryi into OP_TERNARY once support
for 4-in operations are added to the decoder...until then, OP_TERNARY should be
separate from OP_TERNARYI imho.

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