Fundamental concept of time required

Cocotb should have a fundamental concept of time. Currently the Timer() trigger is expressed in simulation time units, however the user has no knowledge of that this is.

We should query the simulator (in VPI we call vpi_get_time with vpiTimeUnit and vpiTimePrecision properties and a NULL handle).

Cocotb can then store the fundamental unit and precision and scale appropriately. In my test I can then specify for example a 6.4ns period clock without needing to know the time precision of the simulator.

[lukedarnell]

I have an implementation that adds convenience functions into cocotb to allow you to easily specify delays in time units.

I’ve currently got something like this:

from cocotb.time import s,ms,us,ns,ps,fs

@cocotb.coroutine
def time_example():
    # Wait 10 seconds
    yield Timer(s(10))
    # Wait 16 milli seconds
    yield Timer(ms(16))
    # Wait 100 micro seconds
    yield Timer(us(100))
    # Wait 5 nano seconds
    yield Timer(ns(5))
    # Wait 2 pico seconds
    yield Timer(ps(2))
    # Wait 1 femto second
    yield Timer(fs(1))

I’m not in love with the syntax of the function calls to generate the simulation time counts. But I’m not sure how else we’d get these numbers. The SystemVerilog time unit syntax would be ideal. e.g

initial begin
    #10s;
    #16ms;
    #2fs;
end

But I’m not sure how’d you achieve something similar in python.

[ktbarrett]

Added sim time with units as a concept to Timer, Clock, and get_sim_time in #474. with_timeout and test timeouts were added in #1119.