seqlogic

Sequential Logic

SeqiLog (pronounced seh-kwi-log) is a Python library for logic design and verification.

Read the docs! (WIP)

Features

SeqiLog provides building blocks to simulate hardware at the register transfer level (RTL) of abstraction:

• Hierarchical, parameterized Module design element
• Four-state bits multidimensional array data type
• Discrete event simulation using async / await syntax

SeqiLog is declarative. To the extent possible, the designer should only need to know what components to declare, not how they interact with the task scheduling algorithm.

SeqiLog is strict. Functions should raise exceptions when arguments have inconsistent types. Uninitialized or metastable state should always propagate pessimistically.

The API is an experiment in how to create a Pythonic meta-HDL. It is currently a work in progress. Expect breaking changes from time to time.

Example

The following code implements a D flip flop (DFF) with the D input connected to the inverted Q output.

from vcd import VCDWriter
from seqlogic import Module, Vec, run, sleep


async def drv_clock(y):
    """Positive clock w/ no phase shift, period T=2, 50% duty cycle."""
    while True:
        y.next = "1b1"
        await sleep(1)
        y.next = "1b0"
        await sleep(1)


async def drv_reset(y):
    """Positive reset asserting from T=[1..2]"""
    y.next = "1b0"
    await sleep(1)
    y.next = "1b1"
    await sleep(1)
    y.next = "1b0"


class Top(Module):
    """Data flip flop (DFF) Example"""

    def build(self):
        clk = self.logic(name="clk", dtype=Vec[1])
        rst = self.logic(name="rst", dtype=Vec[1])
        q = self.logic(name="q", dtype=Vec[1])
        d = self.logic(name="d", dtype=Vec[1])

        # d = NOT(q)
        self.expr(d, ~q)

        # DFF w/ async positive (active high) reset, reset to 0
        self.dff_r(q, d, clk, rst, rval="1b0")

        # Clock/Reset
        self.drv(drv_clock(clk))
        self.drv(drv_reset(rst))


# Run simulation w/ VCD dump enabled
with (
    open("dff.vcd", "w") as f,
    VCDWriter(f, timescale="1ns") as vcdw,
):
    top = Top(name="top")
    top.dump_vcd(vcdw, ".*")
    run(top.elab(), ticks=20)

Use GTKWave or Surfer to view the VCD wave dump. It should look this this:

T (ns)   0  1  2  3  4  5  6  7  8  9 ...
---------+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

clk      /‾‾\__/‾‾\__/‾‾\__/‾‾\__/‾‾\__/‾‾\__/‾‾\__/‾‾\__/‾‾\__/‾‾\

rst      ___/‾‾\___________________________________________________

q        XXXX________/‾‾‾‾‾\_____/‾‾‾‾‾\_____/‾‾‾‾‾\_____/‾‾‾‾‾\___

d        XXXX‾‾‾‾‾‾‾‾\_____/‾‾‾‾‾\_____/‾‾‾‾‾\_____/‾‾‾‾‾\_____/‾‾‾

---------+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

See the ipynb and tests directories for more examples.

Installing

SeqiLog is available on PyPI:

$ pip install seqlogic

It supports Python 3.12+.

Developing

SeqiLog's repository is on GitHub:

$ git clone https://github.com/cjdrake/seqlogic.git

Runtime dependencies are listed in requirements.txt. Development dependencies are listed in requirements-dev.txt.