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chisel

Updating a single bit of a bit vector

Does CHISEL allows only a single bit of a bit vector be updated? I would like to do something like : 

val x = 12
val slot = UInt(0,width=80)
slot(x) := UInt(1)

but the compiler gives the following error:

ambiguous reference to overloaded definition,
[error] both method := in class Bool of type (src: Chisel.Bits)Unit
[error] and  method := in class UInt of type (src: Chisel.UInt)Unit
[error] match argument types (Chisel.UInt)
[error]     slot(x) := UInt(1)
[error]             ^

Is there a better or proper way to do this in CHISEL?

Solution

  • I don't think there is a way to update a single bit at the moment in Chisel.

    EDITED: As of 2014 June, Chisel now allows you to access individual bits of a Reg(UInt()), but not a UInt() wire.

    The way I handle bit vectors is to turn them into a Vec() of Bools/UInts and update them individually that way.

    val x = 12 val slot = Vec(80).fill{Bool(false)} slot(x) := Bool(true) val slot_in_bits = slot.toBits

    You can then use .toBits and .fromBits to move between treating it as a Vec() and treating it as Bits().

    HW-wise, treating a bit vector as a Vec() of bool is equivalent (Unfortunately, in terms of emulation in say C++, it is not super efficient as suddenly each element is its own variable).