Re: [fpu] pipelines & control

[Damjan Lampret <damjanlampret@yahoo.com>]

> > I suggest most of the FPU is controlled by OR1K. If
> > something doesn't
> > require OR1K help then it should be done
> > automatically inside FPU.
> > 
> 
> So could you let us know exactly how exactly should I
> provide for the FPU. This specifications should be
> written in the FPU extrnal interface.
> 

Very simple interface.

Inputs to the FPU:
- operand A (32 bits for single precision FPU)
- operand B (32 bits for single precision FPU)
- type of operation performed (? bits)

Outputs:
- result (32 bits for single precision FPU)
- status flag outputs (overflow, NAN, INF ... you can use your
imagination here)

OR1K issue and completion units will know what gets in the FPU and when
result should come out. If you think calculation times can be variable
for the SAME type of operation then we need extra outputs. Anyway I
really hope that calculation times for the same operation can be always
the same (but of course they can be different for different types of
operations like for fadd vs fmul etc). OR1K core will decide whether
can issue FP instructions or not (detect hazards etc.).

regards,
Damjan


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