Sunday, June 15, 2014

Sequences in UVM1.2

This post concludes our date with sequences in UVM with a quick overview on modifications related to sequences in UVM1.2. UVM that came out with an EA version in 2010 received mass adoption and has matured by the day since then. The working group is all set with another major release(UVM1.2) that should be out anytime. It opened up for public review during DVCON 2014. You may want to dabble with this release and share your feedback here. Given the wide adoption and maturity level, the plan further is to probably take it to IEEE. Victor from eda playground shared interesting insights on what’s new in the UVM1.2 release.  Given below are 4 important changes related to sequences in UVM1.2 –

#1 Setting default sequence from command line [Mantis – 3741]

A new plusarg has been added to the command line to allow setting of default_sequence that the sequencer executes during the start phase. With this change the user can have 1 test with default sequence that can be modified from command line thereby avoiding redundant test development just for changing the default sequence. You can also run regressions by replacing the default sequence with a sequence library (remember sequence library is derived from uvm_sequence).

How was this done in UVM1.1?


Additional control in UVM1.2?

+uvm_set_default_sequence = <seqr>,<phase>,<sequence>

How does it affect current code?

Existing code works without change while you move to UVM1.2. Users are free to choose either of the above. If both are present in the code the result may be a function of phase.

#2 Guarded starting_phase [Mantis – 4431]

The uvm_sequence_base::starting_phase variable is now protected and accessible only via set_starting_phase() and get_starting_phase() methods. One cannot set this variable again if retrieved using get method. The primary reason for this update was that any modification to the starting_phase variable in the code would lead to errors that were hard to debug.

How was this done in UVM1.1?

starting_phase as a variable was used to set phase, compare phase, raise & drop objections

How does it work in UVM1.2?

Use pre-defined methods set_starting_phase() & get_starting_phase()

How does it affect current code?

While moving to UVM1.2, if the code uses starting_phase variable then one can expect compile errors. The Accellera UVM team is generous enough to provide a script as part of the release that searches the starting_phase variable and replaces it with pre-defined methods based on how the variable is used in the code.

#3 Automatic raise & drop objection [Mantis – 4432]

set_automatic_phase_objection() method is added to raise and drop objections based on the starting_phase of the sequence thereby avoiding manual code. This change is mainly for ease of use.

How was this done in UVM1.1?


How does it work in UVM1.2?


How does it affect current code?

The existing code would need modification. As mentioned above, use the script provided by Accellera UVM team as part of the release.

#4 enum changes [Mantis – 4269]

A lot of verification code today involves a mix of different languages, methodologies and code developed by different teams. In UVM1.1 the enum values related to sequences didn’t have a unique signature and this lead to compilation errors when the uvm_pkg was wildcard imported into a scope that already had enum declarations with same name. To avoid this, those enum values are now prefixed with UVM_ string.

How was this done in UVM1.1?

UVM_ prefix missing in enum values for uvm_sequence_state_enum and uvm_sequencer_arb_mode

What changed in UVM1.2?

uvm_sequence_state_enum and uvm_sequencer_arb_mode enum values now have UVM_ prefix

How does it affect current code?

The existing code would give compile errors and you would need to update the values manually.

So when should you move to UVM1.2?

If you are not and early adopter and doesn't enjoy playing with new release, you can hold on for some time; otherwise go ahead, download the release and give it a shot with your code.

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