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Warning example in Software Generator Code-39 in Software Warning example




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Warning example using barcode generating for software control to generate, create code39 image in software applications. iPhone OS A gate-level netlist was ob Software Code39 tained from synthesis after the RTL model had undergone extensive functional simulations. A scan-path and the clock distribution tree were then added by automatic means before physical design was undertaken. Eventually, the extracted netlist was veri ed reusing the logic gauge previously established during RTL simulations.

When prototypes were tested, it was quickly found that they functioned as expected in normal operation mode, but failed to work in scan mode more often than not. What had happened The fact that the clock distribution network had been synthesized before physical layout and not readjusted afterwards had led to moderate clock skew. In normal operation, the contamination delays of the combinational logic present in between the ip- ops proved su cient to compensate for that amount of skew.

In scan mode, in contrast, the rst of two adjoining. 12.1 UNCOVERING TIMING PROBLEMS ip- ops somewhere in the s Software USS Code 39 can chain got clocked with enough positive skew (i.e. before the subsequent one) to cause repeated hold violations in the second ip- op.

Regrettably, the scan mechanism had never been exercised during post-layout simulations as a consequence of reusing the test vectors from RTL simulations where test structures were not yet present. Very much as in the example before, dynamic veri cation missed a timing problem because a critical case was not covered in the test suite. A major di erence is that simulation failed to activate the shortest path this time.

We can also learn from this example that test structures bring about extra hardware with new failure modes.. In conclusion, whether a ti ming problem gets detected during circuit simulation or not depends on several preconditions. For a synchronous design, these include: 1. 2.

3. 4. 5.

Simulations must be carried out at the gate level (rather than transistor or switch level). The models of all subcircuits used must be coded to report all conceivable timing violations. Zero-latency circular paths through combinational subcircuits are disallowed.

The simulator must be properly set up to report unsettled nodes, if any. The longest and the shortest delay must be exercised along every signal propagation path..

Simulation further provides 3 of 9 for None no mechanism that would point to excessively slow clock and signal transitions explicitly. Rather, slow nodes have to be located indirectly from manifestations such as overly long paths, excessive skew, or inadequate waveforms. Attempting to address on-chip variations (OCVs) and crosstalk by way of exhaustive simulations is also impractical.

. 12.1.2 How does timing veri cation help Our discussion has revealed Software Code 39 that simulation alone is not normally su cient to identify timing problems in a digital design. A much better instrument is static timing analysis (STA) or timing veri cation for short. This analytical technique essentially works by mapping the gate-level circuit onto a constraint graph followed by comparing the maximum and the minimum delays along all signal propagation paths in the graph, see gs.

12.2 and 12.3.

For each setup or hold condition, the timewise margin is being obtained as the di erence of the respective delays along two distinct signal propagation paths. To that end each component must be characterized with both propagation delay tpd and contamination delay tcd . A negative result typically indicates a timing violation whereas any positive result is a sign of slack.

Interpretation is actually not quite as simple as not every case of negative slack agged during static analysis necessarily implies that timing violations will indeed develop when the circuit is put to service. This is because certain gate-level circuits include signal propagation paths that are impossible to activate from the inputs [356]. That such false paths do not a ect the maximum admissible clock rate should be obvious.

Similarly, data ranges and formats are sometimes restricted such that not each and every signal propagation path present in a circuit can get exercised in real operation. Designers collect such situations in lists which they feed back into their STA tool in order to exempt false paths from further analysis..

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