Ongoing optimization and verification
previously indicated, the power management scheme starts at the
architectural level, so any available architectural features such as
communication protocols must first be verified.
In the RTL flow,
low-power management constructs are introduced at different phases in
the SoC development, depending upon the data available and the
optimizations required. For example, the team may initially employ clock
gating after devising the initial power architecture. They may then
apply additional power- and/or clock-gating after generation of the
initial power estimate. Usually, a power controller (hardware and/or
software) is inserted to switch off different power domains or to
control the voltages to individual domains. Verification must ensure,
for example, that:
The verification solution
- Normal design functionality is not adversely affected by the addition of power domains and controls.
domain recovers the correct power states at the end of the
power-switching sequence. An incorrect sequence combined with
dependencies between power domains may incorrectly turn on the clock
before removing isolation, corrupting the retention register.
- It achieves a high level of coverage of power-up/power-down events, which are very control-intensive operations.
- Switching off a power domain does not break connectivity between IP blocks.
Any verification solution must address the following diverse needs:
- Analyze and verify architectural features that affect power-aware implementation, such as communication protocols.
and verify common power-aware transformations such as power domains,
supply network and power switching, isolation and retention.
unfamiliar blocks — such as third-party IP blocks — to understand their
behavior sufficiently to modify them according to the power management
- Verify power-related blocks such as clock controllers.
X-propagation analysis to verify X’s at block outputs due to
power-down; and compare differences in output X behavior before and
after application of the UPF/CPF specification.
- Verify the
sequential equivalence of (a) blocks subject to late-stage modification
and (b) blocks before and after power management circuitry is inserted.
connectivity after integration, and ensure that the design complies
with the control and status register (CSR) specification, both before
and after power management insertion.
- Verify power sequencing
during design and after integration, including (a) sequence safety such
as clock deactivation, block isolation and power down, and (b) state
- Verify that memory optimizations do not compromise
functionality. For example, where the original memory is replaced by two
low-power memories with a wrapper, we need to verify that the two
memory models are equivalent to the original memory.