Why did someone decide fractionalBits = binaryPoint? about dsptools HOT 5 OPEN

From a user standpoint, I also find it weird that FixedPoint is a chisel3 thing vs. DspReal is a dsptools thing.

Also, one would think that DspReal and Real are similar, except Real is more like Ring vs. DspReal is more like FixedPoint, SInt, etc.

from dsptools.

One of the motivating factors in the choice of binaryPoint was the desire to support binaryPoints that were negative indicating a virtual exponent. I agree where the various players here (FixedPoint, DspReal) seems a bit arbitrary, but the short term decision was based on how fundamental FixedPoint needed to be in order to properly support it. So it became part of chisel/firrtl, the real stuff was supported by the BlackBox/ExternalModule for chisel/firrtl and did not require any changes. The utility of easily fungible Real/Fixed might argue to bring the real implementation down, but it does not seem to be on the short term critical path.

from dsptools.

@shunshou did you have a specific proposal in this issue? Change the name or simply better doc about the amibguities

from dsptools.

Sorry, ok I forgot about the negative binary points. But yes, if that's fine, please document. I just have to think about that every time I generate FixedPoint (back translate from what I'm used to).

from dsptools.

@chick I got confused again b/c "setBinaryPoint" = set # of fractional bits... Wasn't sure if it trimmed to the right # of fractional bits, shifted the binary point around, etc. etc. It's pretty confusing...

from dsptools.