Structure

Structures describe circuit structure using production rules. Statements in a structure are inherently composed in parallel.

struct structureName(chan<type1> input1) chan<type2> output1 {
    // production rules
}

Production Rules

Each statement follows the format of a production rule.

condition -> action

Condition is evaluated based on valid(). Use true() explicitly to evaluate truthiness. If not specified, assumed to be vdd (always true).

Action is either an assignment, a function call, or a process instantiation.

a & b -> x = 5
z = x + y  // condition is vdd (always true)

The following example implements a single pipeline stage.

• Forwards data from L to R when both are ready (R.e & L.r)
• Acknowledges receipt (R.r -> L.e-)
• Clears output when both are not ready
• Sets enable when output is not ready

struct buffer(chan<int<4>> L) chan<int<4>> R {
    R.e & L.r -> R.r = L.r
    R.r -> L.e-
    ~R.e & ~L.r -> R.r-
    ~R.r -> L.e+
}

We use the buffer to build a first-in-first-out queue.

• Creates an array of intermediate channels M
• Instantiates multiple buffer stages
• Connects them in a chain to create a FIFO queue

struct fifo(chan<int<4>> L) chan<int<4>> R {
    var chan<int<4>> M[5]
    M[0] = L
    M[4] = R

    var buffer stages[4]
    stages[0](M[0], M[1])
    stages[1](M[1], M[2])
    stages[2](M[2], M[3])
    stages[3](M[3], M[4])
}