[libre-riscv-dev] [isa-dev] Re: FP transcendentals (trigonometry, root/exp/log) proposal

MitchAlsup MitchAlsup at aol.com
Tue Aug 13 22:38:21 BST 2019

On Tuesday, August 13, 2019 at 4:05:30 PM UTC-5, lkcl wrote:
> On Tuesday, August 13, 2019 at 11:40:39 PM UTC+8, MitchAlsup wrote:
> > My actual implementation folds ATAN into ATAN2 and changes the last 2 
> lines into::
> Thx Mitch have made a note so it's not lost in list noise.
> Also appreciate the microcode suggestions, have to give that some serious 
> thought, whether to do something truly microcode-like or whether to do just 
> a mini SRAM that contains subroutines that reprogrammable RISCV opcodes can 
> use.
> Much lower level may prove more useful, micro code operations to do FP 
> prenormalisation, post normalisation etc. all at expanded bitwidths.
> L.

The "KIND" of microcode I suggest is the kind where the Calculation Unit is 
microcoded and the data path it sits on remains <whatever it was>. 

Microcoding the main F/D/E part of the pipeline is strongly discouraged.

Think of microcode as if it were a sequencer, just express that sequencer 
in such a way that the synthesizer can implement it with a table, with just 
gates, or with some kind of ROM. Then you don't have to decide if it is 
microcoded (or not) the synthesizer carries the load.

More information about the libre-riscv-dev mailing list