A milestone in functional IC verification was reached today
(May 17, 2010) as Accellera released
the Universal Verification Methodology (UVM) version 1.0 EA ("early adopter") to
the verification community. Here's some background on how this happened, why
it's important, and how it impacts current users of the Open Verification Methodology
(OVM) and the Verification Methodology Manual (VMM).
During the past two years, the Accellera Verification IP (VIP) Technical
Subcomittee has been working to drive the industry towards a single
standard verification methodology based on SystemVerilog. That's because two
different, incompatible formats have emerged. These are the OVM, backed by Cadence and Mentor Graphics,
and VMM, backed by Synopsys. As a result, the reuse of verification testbenches
and VIP has been difficult. To find a solution, Cadence, Mentor and Synopsys joined together in
support of the VIP subcommittee.
Last year the VIP subcommittee released a Recommended
Practices interoperability guide. It shows how VMM testbenches can work
with OVM VIP, and vice versa. But the more ambitious mission has been to create
a single SystemVerilog methodology standard with a common base-class library,
and bring it to the IEEE for standardization. This effort became known as
"UVM." Last December, the VIP subcommittee voted
to make the OVM the basis of UVM.
The work done by the Accellera VIP subcommittee has been
"phenomenal," according to Adam Sherer,
product manager at Cadence and secretary of the VIP subcommittee. In most
standards efforts, he noted, there is a "lowest common denominator" solution,
but the verification experts who staffed the committee made it clear that
wasn't going to happen here. The committee built a new standard in just five
And not just any standard, Adam noted - this is the first
time that Accellera has created complex software for the industry to download
and use. Normally Accellera, like other standards organizations, has produced
reference documents. Offering software mandated new procedures for gathering
requirements, building specifications, implementation, and testing.
Impact on OVM Users
Current OVM users have it easy. UVM 1.0 EA is essentially
OVM 2.1.1 with a few additions. UVM 1.0 EA is a clean superset of OVM 2.1.1,
and it offers backwards compatibility with OVM. Since OVM 2.1.1 is in
production flows today, and anything that's been added is clearly identified in
the release notes, the so-called "early adopter" release of UVM is really
production-ready, Adam said. Cadence tools will support it immediately.
Most current OVM users will probably wait until their next
project starts to move to UVM. One small difference is that base class names in
UVM start with a "U" instead of an "O." Cadence will provide a script that can
automatically make that change.
Callbacks are provided in UVM 1.0 EA. They're also in OVM
2.1.1, but not in OVM 2.0.3, which is still widely used. Callbacks enable
testbench applications, such as scoreboards, to be alerted when events occur in
the design or in the testbench itself. One VMM feature that was not part of
OVM, and has been added to UVM 1.0 EA, is a "report catcher" API. This is a
mechanism for filtering out types of warning messages that the user identifies
Impact on VMM Users
The migration for VMM users is going to be more difficult.
There are, however, ways to make the transition to UVM, and you can expect to
see webinars, blogs and other documentation become available in the near future. VMM
does support callbacks so that feature, at least, should be familiar in UVM.
Next Step - A
There's still more work to be done, and the hottest topic
right now, according to Adam, is identification of a UVM register package. In a
testbench, the operating conditions of the design are set up through registers,
and engineers need to know where the registers are, what the fields are, and
how values are recognized and set. This is accomplished with a register
package. Today, these packages are provided separately by EDA vendors.
How important is it? Verification consultant J.L. Gray ran a
survey in his Cool Verification
blog, and 57 percent of respondents identified a UVM register package as
"critical." Adam observed that the IP-XACT standard developed by the SPIRIT
Consortium, which has merged with Accellera, provides a good basis for
supporting a register package, but will need some extension.
Other future topics include transaction-level modeling (TLM
2.0) functionality and support for multiple verification languages. But I think
we can stop for a moment and appreciate how far the UVM standardization effort
has gotten in such a short period of time.
The Accellera UVM 1.0 EA software is available without charge using
the Apache 2.0 license.The release contains the UVM library, examples, the user
guide (which is virtually the same as the OVM User Guide), the reference
manual, and the release notes.