What is IEEE 1801-2013?
IEEE 1801-2013 is the latest version of the power-intent description standard for low-power VLSI design that started life as the Unified Power Format (UPF), and is sometimes referred to as UPF 2.1. The previous version, IEEE 1801-2009 was also known as UPF 2.0. The latest version of the standard incorporates elements of the Common Power Format (CPF), which is managed by the Silicon Integration Initiative (Si2).
The emphasis of the latest version of the standard focuses on usability in industrial designs, restricting some of the freedom of the command set but providing better guidance for design teams trying to design ICs with complex power modes and behavior. As a language level, the command set has been structured to support successive refinement of power intent to reduce the usage overhead on design teams.
What has changed?
Changes in IEEE 1801-2013 took advantage of industrial experience and a wider user base to perform a cleanup of the original standard, as well as adding new commands to support incremental specification of power modes and behavior. A number of commands that were defined in previous versions of the standard have been deprecated or treated as ‘legacy’. Deprecated commands should be replaced as soon as possible in current designs as future support cannot be guaranteed. Legacy commands are fine for existing modules but are not recommended for new design modules.
Several informative annexes have been added to the standards document, such as Annex E, which provides a low-power design methodology based on the standard, and Annex I, which provides examples of how to model power-management cells.
IEEE 1801-2013 attempts to improve support for power modelling, implementation and verification throughout the lifecycle of an IC design. An important underlying concept is that of incrementality, to allow the design to be gradually elaborated over time as more implementation detail is added without forcing engineering teams to keep rewriting the command scripts.
Instead, precedence rules are used to allow later, more detailed UPF commands to override generic commands that may have been inserted earlier to support behavioral logic simulation. The way in which UPF commands override each other is expressed through precedence rules. For example, a generic command may set a ‘strategy’ for how to apply isolation, retention and other power-domain functions to an entire domain. This strategy can be overridden for a named port on that domain, which in turn may be overridden by a command that specifies individual bits within a multibit port.
Similarly, the structure for strategies is organized to allow high-level verification before implementation details are in place, and to avoid a decision later on from affecting the validity of that simulation. In general, retention strategies influence repeater, isolation and level-shifter strategies in turn.
A number of features have been added to better support design reuse and commercial IP, including the ability to set constraints on usage.
Hard macros presented a problem for earlier versions of UPF if those macros implemented their own power-management as switchable power domains were the only way to define power supplies to domains that could be powered up and down. The new version provides the ability to set power attributes on ports that are managed inside the macro.
Atomic power domains provide greater control for IP providers by preventing users from subdividing a domain so that the different parts are power-gated separately if that is not explicitly supported by the IP. Attempting to create power domains inside an atomic domain will generate an error in compliant tools.
A further addition is the concept of supply equivalence, in which supply nets can be treated as electrically or functionally equivalent to reduce the number of source and sink attributes that need to be defined. Equivalence can be overridden in scripts to provide greater control over strategies.
Where can I find it?
The latest revision of the IEEE 1801 Unified Power Format standard for verifying low-power designs has been made available through the IEEE’s Get Program, which provides free public access to selected standards. Users can each download a single copy of IEEE 1801-2013 by providing an email address at the Get website.
Who supports it?
Cadence Design Systems, Mentor Graphics and Synopsys, as well as Aldec and Docea Power, have declared they aim to support for IEEE 1801-2013. Specific support for individual aspects of IEEE 1801-2013 are currently unclear.