[VTA] add support to event counters

[vegaluisjose]

This PR adds infrastructure (software and hardware) to support event counters in the VTA Chisel implementation. Only counting cycles at the moment.

This is how cycles are now displayed on vta unittest (test_vta_insn.py)

$ python3 test_vta_insn.py
Initialize VTACommandHandle...
Load/store test took 619 clock cycles
Padded load test took 8579 clock cycles
GEMM schedule:default test took 648 clock cycles
GEMM schedule:smt test took 755 clock cycles
ALU SHL imm:True test took 1067 clock cycles
ALU MAX imm:True test took 1067 clock cycles
ALU MAX imm:False test took 1654 clock cycles
ALU ADD imm:True test took 1067 clock cycles
ALU ADD imm:False test took 1654 clock cycles
ALU SHR imm:True test took 1067 clock cycles
Relu test took 1738 clock cycles
Shift/scale test took 386 clock cycles
Close VTACommandhandle...

[tmoreau89]

One question regarding the event counters in this example: does cycle count get reset every time we invoke the simulator on a new "workload"?

[tmoreau89]

I suggest that @tqchen also takes a look at how profile information is retrieved

[tmoreau89]

It appears that we are not returning a dictionary here; perhaps we should to accommodate for more profile information (and use the "cycles" as a key for the cycle count)

[vegaluisjose]

We are not because I am just returning a cycle element at the moment. I was thinking that once we think on a second counter, we can added then.

[vegaluisjose]

The event counter can be set to zero from software and hardware. In this particular case, the counter is counting only when this condition is met

  when (io.launch && !io.finish) {
    cycle_cnt := cycle_cnt + 1.U
  } .otherwise {
    cycle_cnt := 0.U
  }

This basically means when VTA launches but is not finished. I also added this to tsim-driver just to show how to set the counter from zero but in this case really does not matter.

Also, the idea of this PR is to provide a mechanism (hardware) that can automatically generate event-counter-register and map addresses accordingly in hardware, see how the VCR looks now

The "final" take on the number of counters and what we would want to count should come next after this.

[jroesch]

Can we talk a little bit about how we add a new counter, maybe pointers to the places that need to be changed? it looks like the event count vector has a length set somewhere?

[vegaluisjose]

Sure, I can add more. The ecnt vector params are taken from here

see Line 38 from link above

  val vp = p(ShellKey).vcrParams

The design patter around params is that every time you see something like myModuleParams" somewhere, then you should go to myModule` to see what parameters are defined there.

The idea here is that if the number of event counters or nECnt is changed in VCR then the interface will automatically change as well, without needing to do it manually. The EventCounters.scala file will just implement "what you want to count" logic.

[vegaluisjose]

Also, I just added a little bit of more info on how to add counters.