Support `attach`

[edwardcwang]

e.g. the following line is not recognized by the visualizer

attach (pll.vdd, vdd) @[DigitalTop.scala 108:11]

[chick]

I haven't seen this construct, can you send me the full firrtl file. I will need to see how this thing gets lowered to figure out what's going on. Thanks

[edwardcwang]

Here's a very minimalistic example that just attaches two IOs:

FIRRTL:

circuit AttachTest : 
  module AttachTest : 
    input clock : Clock
    input reset : UInt<1>
    output io : {in : Analog<1>, out : Analog<1>}

    attach (io.in, io.out) @[cmd8.sc 6:9]

Chisel:

class AttachTest extends Module {
  val io = IO(new Bundle {
    val in = Analog(1.W)
    val out = Analog(1.W)
  })
  attach(io.in, io.out)
}

[chick]

I'll fixit, I'm curious why you put this issue on chick/visualizer instead of freechipsproject/diagrammer. Accident?

[chick]

@edwardcwang is this the only use case for attach, there is very little documentation, what should it do? Unlike connect it takes a list of expressions, not an lhs and rhs like connect

[edwardcwang]

W.r.t putting the issue here:

1) Github says that chick/visualizer is the upstream and freechipsproject/diagrammer is a fork. If the freechips one is meant to be the authoritative upstream then we should delete that and move this repo there.

2) The issues tab is missing for me in freechipsproject/diagrammer

[edwardcwang]

Attach is used to connect Analog nets together. It is a multi-way, undirectioned connect.