Using input types to index Array register gives TypeError about magma

[leonardt]

Is the idea here to dynamically set one index of arr? If so, you could try using set_index

magma/magma/primitives/set_index.py

Lines 7 to 13 in e0a49bb

	def set_index(target: Array, value, idx: UInt):
	"""
	Returns a new value where index `idx` of value `target` is set to `value`
	* `target` - a value of type `Array[N, T]`
	* `value` - a value of type `T`
	* `idx` - a value of type `UInt[clog2(N)]`
	"""

class Test1(m.Circuit):
    io = m.IO(
        A=m.In(m.UInt[2]),
        B=m.In(m.UInt[4]),
        O=m.Out(m.UInt[4]),
    )
    arr = m.Register(m.Array[4, m.UInt[4]])()
    arr.I @= m.set_index(arr.O, io.B, io.A)
    io.O @= arr.O[0]

I'll have to investigate this error which is not very helpful, but I don't think this syntax would necessarily work in general because you'd want to specify a default value for the values that aren't written. The function set_index style implies that the value is unchanged for the indices which I think is more explicit.

[rkshthrmsh]

Hi @leonardt, yes, the intention was to dynamically set specific indices of a register array. As you mentioned, in the arr.I[io.A] @= io.B syntax, not specifying a default value for other indices is the issue.

In a Register, could the previous O values be considered as the default for Is that are not explicitly wired? Are there potential issues with that?

[rkshthrmsh]

As an extension, how can one dynamically set an index of an N-D array?
Based on the function signature of set_index, it appears that idx is UInt only.

class Test1(m.Circuit):
    io = m.IO(
        X=m.In(m.UInt[2]),
        Y=m.In(m.UInt[2]),
        B=m.In(m.UInt[4]),
        O=m.Out(m.UInt[4]),
    )
    arr = m.Register(m.Array[(4, 4), m.UInt[4]])()
    # Intention:
    # arr.I[io.Y][io.X] @= io.B
    arr.I @= m.set_index(arr.O, io.B, (io.X, io.Y)) # TypeError: Expected value to be the same type as `target`'s contents
    io.O @= arr.O[0][0]

[rkshthrmsh]

Figured out this can be done recursively like so:

    arr.I @= m.set_index(arr.O, m.set_index(arr.O[io.Y], io.B, io.X), io.Y)
    # Equivalent to:
    # arr.I[io.Y][io.X] @= io.B and all other inputs wired to defaults

However, the syntax can look messy when dealing with N-D arrays having multiple indices. Thought it might be better to simplify it to:

    arr.I @= m.set_index(arr.O, io.B, [io.Y, io.X])

Have opened a PR for this #1330.

[rkshthrmsh]

Merged in #1353