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ARM last week announced
the first phase of its AMBA 4 specification, and Cadence simultaneously released
verification IP (VIP) for the e language and SystemVerilog. So why
is ARM releasing AMBA 4, what's in the two phases, and what's in the VIP? To
get a closer look at what's in the AMBA 4 specification I talked to Keith
Clarke, vice president and general manager of Fabric IP at ARM's Processor
The widely-used AMBA 3 spec has been around since 2003, and
it was time for an upgrade, Keith said. He noted that AMBA 4 was developed in
conjunction with some 35 partners, including Cadence. A big motivation, he
said, is the increase in performance of processor cores, as well as the ability
to place multiple cores on SoCs and to support many different functions on a
Additionally, the phase one release that was disclosed last
week adds new support for FPGAs. Phase one includes the AXI4, AXI4-Lite, and
AXI-Stream protocols. The phase two release, which will be disclosed later this
year, will bring in features that will help users develop and program multicore
product line manager for VIP at Cadence, said he is "definitely seeing
interest" among the customer base for AMBA 4. "The traditional mobile guys are currently
planning their roadmaps for it," Pete said. What's attracting customers, he
said, is increased performance, along with a hoped-for power savings.
AXI4 is an incremental and backwards-compatible update to AXI3
that improves performance and interconnect utilization for multiple masters. It
supports burst lengths of up to 256 beats (data packets). Previous support only
went up to 16 beats. "We don't foresee ARM processor requests for 256 beats of
data, but we do foresee certain types of masters, in certain types of
applications, that do need these long transactions of data," Keith said. An
example, he said, could be a data interface in a networking application.
AXI4 also adds quality-of-service (QoS) signaling and
support for multiple-region interfaces.
This is a subset of AXI4 designed for communication with
simpler, smaller control register-style interfaces. It can reduce the number of
wires required to access "peripherals that have simpler needs." While designed
with FPGAs in mind, "there is nothing to stop it being used for SoCs," Keith
In this protocol, all transactions have a burst length of
one, all data accesses are the same size as the width of the data bus, and
exclusive accesses are not supported.
This protocol, unlike AXI4-Lite, is not a strict subset of AXI4. Designed primarily with FPGAs in mind,
it aims to greatly reduce signal routing for unidirectional data transfers from
master to slave. The protocol lets designers stream data from one interface to
another without needing an address, Keith said. It supports single and multiple
data streams using the same set of shared wires.
AMBA 4 Phase Two - Simplifying
Multicore SoC Design
ARM is not saying much about AMBA 4 phase two now, but the
company has noted that it will provide hardware support for cache coherency and
message-ordering barriers. By putting more capabilities in hardware, AMBA 4
will simplify multicore programming. Keith said phase two will "have quite a
lot of new technology for coping with multi-master systems."
Cadence Incisive VIP support is "really important," Keith
said. "Cadence announcing so quickly is really good news for our customers who
want to get a start on designing with AMBA 4." Verification IP, Keith noted, is
increasingly important because "the complexity of devices has gone up, and
people need to know when they attach various design IP blocks together that
they are actually talking the same language."
Pete Heller said
that the Cadence
AMBA 4 VIP is currently available as part of an early access program for
customers. It will be in production later in the year. In addition to the testbench VIP that is available today,
Cadence will also provide assertion-based VIP for formal verification and
transaction-based VIP for system-level verification. The VIP is OVM-compliant
and will include the Cadence Compliance Management System (CMS), which supports
verification planning and metric-driven verification.
Pete noted that Cadence AMBA 2 and AMBA 3 VIP has nearly a
10 year track record and has been used in well over 1,000 projects, and he said
Cadence is regularly working with ARM to ensure the highest quality and to support
phase two of the AMBA 4 release with VIP. A Team
Specman blog has more details about the AMBA 4 VIP and tells how you can
request early access.