Multimode Clock Domain Crossing – Verix CDC2019-03-13T03:54:59+00:00

Verix CDC – Multimode Cross Domain Crossing

White Paper: True Multimode CDC Signoff

Multimode Clock Domain Crossing Sign-off

Taking Real Intent’s industry leading Meridian CDC to the next level, Verix CDC  is the fastest, highest capacity and most precise solution for multimode CDC solution in the market.

Specially architected for multimode clock domain crossing analysis, Verix CDC performs comprehensive CDC analysis with multiple clocks reaching the flops, allowing all possible scenarios to be covered in a single run.

Verix CDC’s deep static analysis engines interpret multimode clock structures, and automatically eliminate impossible clock and data combinations to generate high precision report which provide true multimode CDC sign-off.

Why Multimode?

Current single-mode methodology for CDC sign-off uses SDC constraints with case analysis for each mode. That necessitates the reviewing of CDC issues in each mode separately and several iterations to ensure that all modes are clean. With the rapid rise in the number of modes, it is nearly impossible to sign-off each mode individually. In addition, static timing analysis, traditionally done in single mode, has already moved toward multimode analysis. As a result, multimode SDC is more readily available to start multimode CDC sign-off.

Multiple clocks feed into the flops

In single-mode CDC sign-off, multiple runs of CDC analysis are needed for sign-off. As shown in Figure 1, the data crossing from FF1 to FF2 will be reported only if sel is set to 0. In multimode, CDC sign-off can be achieved in a single CDC run. No clock selection through sel is needed and the data crossing from FF1 to FF2 will be reported.

Verix Multimode CDC Automatically understands impossible clock combinations

True Multimode CDC Sign-off

In Verix CDC analysis is performed using multiple clocks reaching the flops. SDC constraints are applied without mode select, allowing multiple clocks to propagate to the flops.

Verix CDC’s deep static analysis technology can automatically deduce whether certain clock interactions are not possible in certain logic areas of the design.

The technology automatically infers and applies the logical and graphical relationships between clocks to enable true multimode clock domain crossing sign off.

High Precision, Low Noise Results

In multimode, as the amount of CDC analysis data can increase manifold, the multimode CDC tool must be highly precise, so it leads to an efficient CDC sign-off. Verix CDC’s proprietary technology has a holistic view of all the modes in the design which enables it to generate a high precision report in a single run.

It reports an error if a CDC issue exists in any one of the modes. It reports path as CDC safe only if the path is correct in all the modes. Verix CDC’s deep static analysis technology can automatically interpret the CDC handshake structures in multimode context leading to low noise reports.

Automatically interprets CDC handshake structures in multimode

Comprehensive CDC Sign-off

In addition to metastability, clock domain crossings can introduce other catastrophic failures in the design.

Verix CDC comprehensively analyses clock/reset structures and identifies all possible CDC issues including incorrect or missing synchronization, glitch potential, reconvergence, structurally unsafe crossings, and potential data/control crossings that need functional verification.

Verix CDC supports Verilog, VHDL, and System Verilog languages and standard SDC or TCL format to read design constraints.

With Verix CDC, all CDC checks are enabled in multimode

Efficient Multimode CDC Debug

Verix CDC’s multimode reporting keeps users focused on important multimode CDC analysis issues through an efficient organization of the results of the analysis. Helpful guidance and suggested actions help users pinpoint the source of the problems quickly. Real Intent’s state-of-the-art design-intent debugger and analysis manager—iDebug—provides for user configurability and programmability with its command-line interface (CLI).

Verix CDC supports an integrated visualization tool. Annotated and pruned schematic views focus on fault-related logic, and with a few mouse clicks, users are directed to the RTL source code that caused the problem. This debug approach allows for easy investigation deep into the design to isolate the root cause for any warnings and errors. As shown the Figure 2, the CDC violations are reported with multiple interacting clocks. Users can view further details and the in-context schematics.

Annotated & pruned schematic in iDebug
(Click to Enlarge)


  • Most precise multimode CDC reporting—no crossing missed
  • Deep static verification technology provides unprecedented precision, ease of use, and debug
  • Automatic identification of impossible clock combinations
  • Automatic interpretation of CDC handshake structures in multimode context
  • Comprehensive: All CDC checks enabled in multimode
  • Efficient debug, especially architected for multimode CDC sign-off


  • Reduces runtime by a factor of number of modes
  • Require single setup for multimode
  • Saves debug time by avoiding analysis of crossings that cannot occur, iterations, and duplication of reviews
  • Fastest performance for quick clock domain crossing sign-off turnaround
  • Highest capacity to enable CDC verification of billion-gate SoC designs
  • Most precise CDC reporting using integrated analysis
  • Easiest-to-use CDC solution in the industry, and is template free