There must be no no asynchronous inputs: they must be properlyīuffered to implement synchronous input signal delays. Inputs governed by the same single clock frequency. For example, only the rising edge of the clock is triggered.Īll combinatorial logic outputs are computed from sequential logic There is only a single clock frequency governing sequential logic.Īll sequential logic actions are triggered on the same edge of theĬlock. This simulation convention is an accurate and computationallyĮfficient model of how the real hardware would behave: However, under a very restricted set of conditions, You’re getting the wrong idea of how the circuit will work in hardwareĪt face-value. The problem with this method of simulation is obvious. But, in fact, there is an infinitesimal delay between VCD oscilloscope traces, it will appear as if the new output value isīeing propagated on the same rising edge of the clock where you areĬomputing it. Values second, but because it will be so fast, when you look at the Retrieve the old register values first, then write the new register So, this means… in simulation, all non-blocking assignments will Timescale to be substantially smaller than your clock period. The simulation time cycle granularity is derivedįrom your timescale specification, and generally you specify your Simply “as short of a delay as possible,” namely the very next Immediately, and the output is assigned after a delay.” But, whatĮxactly is that delay? If no delay is explicitly specified, this is Non-blocking assignments as follows: “the input value is evaluated As a simulation platform, Verilog is specified to execute Output value change? Verilog turns out to be pretty tricky in this So, what happens here? When is the input value read, when does the
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