wishbone.bus: add Arbiter.

[jfng]

Wednesday Jan 22, 2020 at 14:18 GMT Originally opened as m-labs/nmigen-soc#3

This arbiter should be compatible with all the optional features of wishbone.Interface.

The round-robin implementation could perhaps be moved to nmigen.lib and imported back here, but that would make nmigen-soc depend on a later revision than nmigen v0.1.

[codecov[bot]]

Codecov Report

Merging #9 into master will increase coverage by 0.04%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master       #9      +/-   ##
==========================================
+ Coverage   99.59%   99.63%   +0.04%     
==========================================
  Files           4        4              
  Lines         493      552      +59     
  Branches      107      127      +20     
==========================================
+ Hits          491      550      +59     
  Misses          1        1              
  Partials        1        1

Impacted Files	Coverage Δ
nmigen_soc/wishbone/bus.py	98.97% <100%> (+0.44%)	:arrow_up:

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[jfng]

Thanks for the review !