If such a scenario is never expected from the design, the property of the design that only valid instructions can be read from memory is violated and the assertion fails.Īs evident from the two examples above, properties of a given design is checked for by writing SystemVerilog assertions. For example, assume a small processor decodes instructions read from memory, encounters an unknown instruction and results in a fatal error. If a property of the design that is being checked for by an assertion is forbidden from happening, the assertion fails. But if the design gets an ack on the fifth cycle, the property that an ack should be returned within 4 clocks is violated and the assertion fails. For example, assume the design requests for grant and expects to receive an ack within the next four cycles. If a property of the design that is being checked for by an assertion does not behave in the expected way, the assertion fails. Hence assertions are used to validate the behavior of a system defined as properties, and can also be used in functional coverage. The behavior of a system can be written as an assertion that should be true at all times. and should not have posedge/negedge at any posedge clk This sequence states that 'a' should be stable on every clock "testbench.sv", 12: tb.unnamed$$_0: started at 170ns failed at 170ns "testbench.sv", 12: tb.unnamed$$_0: started at 30ns failed at 30ns This is because value of a is 1 at 130ns and 0 at 150ns upon which the assertion completes and is proven to be successful.Ĭompiler version P-2019.06-1 Runtime version P-2019.06-1 Jan 14 07:09 2020
See that a negative edge was detected and the assertion passed at 1500ns in the image shown below. negedge 'a' is not found on every posedge clk This sequence states that 'a' should fall on every posedge clk So, this requires 2 clocks to be identified. When value of the signal is 1 on the first edge and then 0 on the next edge, a negative edge is assumed to have happened. Because SystemVerilog assertions evaluate in the preponed region, it can only detect value of the given signal in the preponed region. In this case $fell of a indicates that a negedge of a is expected to be seen on every posedge of clk. The system task $fell is used to detect negative edge of the given signal. "testbench.sv", 12: tb.unnamed$$_0: started at 190ns failed at 190ns "testbench.sv", 12: tb.unnamed$$_0: started at 130ns failed at 130ns "testbench.sv", 12: tb.unnamed$$_0: started at 110ns failed at 110ns "testbench.sv", 12: tb.unnamed$$_0: started at 90ns failed at 90ns "testbench.sv", 12: tb.unnamed$$_0: started at 70ns failed at 70ns "testbench.sv", 12: tb.unnamed$$_0: started at 50ns failed at 50ns The behavior is visible in the simulation log where assertion failed at all times other than 30ns and 170ns. This is because value of a is 0 at 10ns and 1 at 30ns upon which the assertion completes and is proven to be successful. See that a positive edge was detected and the assertion passed at 30ns in the image shown below. posedge 'a' is not found on every posedge clk When the above sequence is asserted, the assertion fails if This sequence states that 'a' should rise on every posedge clk When value of the signal is 0 in the first edge and then 1 on the next edge, a positive edge is assumed to have happened. In this case $rose of a indicates that a posedge of a is expected to be seen on every posedge of clk. The system task $rose is used to detect a positive edge of the given signal.
$finish called from file "testbench.sv", line 27. "testbench.sv", 12: tb.unnamed$$_0: started at 150ns failed at 150ns "testbench.sv", 12: tb.unnamed$$_0: started at 10ns failed at 10ns
0 kommentar(er)
