SystemVerilog Assertions: Delay, Repetition, and Status

📈 Assertion Status

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During the execution of an assertion, we can track various statuses:

• Succeeded (pass): The assertion worked as expected.
• Failed: The assertion condition was not met.
• Inactive: The assertion is disabled or not triggered.
• Active: The assertion condition is being checked; the assertion is triggered and running.
• Enabled: The assertion is in an enabled state and ready to trigger when its condition occurs.

⏳ Cycle Delay Repetition

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In a sequence or assertion, cycle delay expressions can be used to define delays across successive clock cycles.

Example:

sequence s_delay;
  a ##2 b;
endsequence

In this example, b is checked 2 cycles after a occurs.

🔄 Cycle Delay Repetition Ranges

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Using a range in delays allows us to define more flexible checks:

sequence s_range;
  a ##[2:4] b;
endsequence

Here:

• b is checked 2 to 4 cycles after a occurs.

🔁 Consecutive Repetition

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Consecutive repetition checks whether an event occurs continuously over consecutive cycles.

Example:

sequence s_consec;
  (a && b)[*3];
endsequence

Here:

• The expression a && b must be true for 3 consecutive cycles.

🔂 Consecutive Repetition with Ranges

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You can also use ranges in consecutive repetitions:

sequence s_consec_range;
  (a && b)[*3:5];
endsequence

In this example:

• The expression a && b must be true for 3 to 5 consecutive cycles.

🚦 Consecutive Repetition: Special Ranges

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For special repetitions:

• [*] ➔ 0 or more consecutive cycles.
• [+] ➔ 1 or more consecutive cycles.

Example:

sequence s_star;
  a[*];
endsequence

sequence s_plus;
  b[+];
endsequence

⏸️ Nonconsecutive Repetition

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Nonconsecutive repetition (or non-monitored repetition) checks whether an event occurs the desired number of times without requiring consecutive cycles. This typically uses the throughout or within keywords (advanced usage). Simple example:

sequence s_nonconsec;
  a ##[1:$] b;
endsequence

Here:

• After a occurs, b is checked at least 1 cycle later, up to infinity.

🌀 Go-To Repetition

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Go-To repetition allows an event to overlap in consecutive cycles, starting new instances. This is often used in FSM state assertions.

Example:

sequence s_goto;
  a ##1 b [->3];
endsequence

In this example:

• The b signal is checked 3 times with parallel instances overlapping.

🔀 Go-To and Nonconsecutive Ranges

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Go-To repetition also supports ranges:

sequence s_goto_range;
  a ##1 b [->2:5];
endsequence

Here:

• The b signal starts between 2 and 5 overlapping instances (non-deterministic).

📊 Repetition Table

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