How to understand this line of chisel code

Question

I'm in the process of learning chisel and scala language and try to analyse some lines of rocket-chip code.Could anyone try to explain me this line? https://github.com/chipsalliance/rocket-chip/blob/54237b5602a273378e3b35307bb47eb1e58cb9fb/src/main/scala/rocket/RocketCore.scala#L957

I understand what log2Up function is doing but don't understand why that log2Up(n)-1 and 0,were passed like "arguments" to addr which is val of type UInt!?

This is how you perform bit-slicing in chisel. It calls the apply function on UInt (the variant with with two integer arguments, namely the upper bound and the lower bound) and will basically give you the n least significant bits of addr. — ɹɐʎɯɐʞ
Another tip that might help is that due to register 0 being hardcoded to 0 in the RISC-V ISA, Rocket's register file uses a little trick where it reverses the order of the registers physically compared to the RISC-V spec. x1 is index 31 in rf while x31 is index 0. — Jack Koenig

yatsukha yatsukha · Accepted Answer · 2019-11-11T18:14:26

I could not find where UInt was defined, but if I had to guess, UInt is a class that has an apply method. This is a special method that allows us to use a parenthesis operator on an instance of the class.

For example lets say we have a class called Multiply that defines an apply method.

class Multiply {
  def apply(a: Int, b: Int): Int = a * b
}

This allows you to call operator () on any instance of that class. For example:

val mul = new Multiply()
println(mul(5, 6)) // prints 30

How to understand this line of chisel code

2 Answers