Multiplexer function and process unit

[ryukzak]

We need to design:

• Multiplexer function:
  • Multiplexer :: { inputs :: [I v], sel :: [I v], out :: O v }
• Multiplexer PU for it. Here we have a lot of options on internal design, depends from the protocol (we need to start with simplest one). Few examples:
  • Load selector and save it -> Load inputs and save only selected input (can be an extended FRAM) -> output saved value.
  • Load inputs and save all of them, Load selector and save it, output value by selector. Loading sequence not restricted.
  • Combination of them, depends from scheduling.
  • Multiple functions at one time.
  • How many options we provide? Simplest -- two. But what about switch? Maybe, it should be a part of comporator PU?
• support in lua frontend <, <=, ==, >=, >.
• tests