VHDL/HDL PROCESS semantics: Within a PROCESS, VARIABLES are considered to update ________ as statements execute, whereas SIGNALS referenced inside the same PROCESS update when the PROCESS ________.

Introduction / Context:
In VHDL (and similarly in many HDL teaching contexts), SIGNALS and VARIABLES have different update semantics. Misunderstanding this distinction is a common source of simulation mismatches and timing bugs. Knowing when each is updated helps you write predictable synchronous and combinational processes.

Given Data / Assumptions:

• We are discussing code inside a single PROCESS.
• VARIABLE assignments take effect immediately for subsequent statements in the same PROCESS activation.
• SIGNAL assignments schedule updates that become effective when the PROCESS suspends (e.g., after wait/event) and resumes in the next delta cycle.

Concept / Approach:
A VARIABLE is local to the PROCESS and behaves like a software variable: when you assign to it, the new value is used by the next statement in that PROCESS activation. A SIGNAL represents a hardware wire/register; assigning to it does not instantly change its value for the remainder of that activation. Instead, the new value is queued and applied at PROCESS suspension, ensuring deterministic delta-cycle behavior and preventing races among concurrent statements in different processes.

Step-by-Step Solution:

Verification / Alternative check:
Simulate a simple counter where a variable accumulates sum and then assigns to a signal at the end of the PROCESS. Watch waveforms: the signal updates at suspension; intermediate variable changes are not visible outside until the final signal assignment posts.

Why Other Options Are Wrong:

• “Once, starts” / “Twice, ends” / “Never, starts”: These do not reflect actual VHDL semantics.
• “Immediately, resets”: Signals do not wait for a reset; they update at suspension/delta cycle.

Common Pitfalls:
Expecting signals to change immediately inside the PROCESS; chaining multiple signal assignments and assuming earlier ones are visible to later lines; forgetting that variables are not visible outside the PROCESS unless copied to signals.

Final Answer:
Immediately, suspends