Setup/Hold Characterization

008_cell : Setup/Hold Characterization

Minimum Required Versions: AccuCell 2.6.0.R, SmartSpice 4.6.2.R

This example explains the basics of AccuCell's setup and hold characterization and modeling options for a basic D Flip-Flop with rising edge clock using the embedded SmartSpice SPICE engine to perform characterization.

Characterization options specifically for controling the various setup/hold conditions separate from the rest of the basic combinational delay and power parameters can be defined in the Cell_EX8.cfg file using the SETHOLD_, SH_ parameters. The main parameters are SH_SLOPE_TABLE, SH_CLK_SLOPE_TABLE, SH_DATA_SLOPE_TABLE, SETHOLD_DIMENSION, SETHOLD_ACCUR, SETHOLD_MAXIT. Others control more advanced characterization effects such as clk-to-Q degradation, Recovery/Removal and minimum pulse widths. Additional control options will be explained in more detail in a separate web-examples.

SH_SLOPE_TABLE specifies the clk AND data pin slopes for setup/hold (and recovery/removal) characterization and modeling.

SH_CLK_SLOPE_TABLE specifies ONLY the clk pin slopes, which are commonly restricted to about half the slope range (or less) of the data pins to ensure clocks have well defined edges and to improve table interpolation errors for the critical clock paths.

SH_DATA_SLOPE_TABLE specifies ONLY the data pin slopes

SETHOLD_DIMENSION specifies the structure of the setup/hold (and recovery/removal) timing constraint tables. The use of 2D (or 3D) tables permits taking into account clk vs data slope timing dependency effects which can be significant.

SETHOLD_ACCUR specifies the accuracy threshold for terminating the bisection iteration search for the setup/hold (and recovery/removal) tolerance. Smaller values will require more iterations to reach their error goal.

SETHOLD_MAXIT specifies the maximum number of bisection search iterations for setup/hold (and recovery/removal) to control runtime and in case of cell characterization failure before accepting a final value or bypassing the characterization for the next arc or cell condition.