188.8.131.52. Optimize Hold Timing
When you turn on Optimize Hold Timing in the Advanced Fitter Settings dialog box, the Intel® Quartus® Prime software adds delay to paths to ensure that your design meets the minimum delay requirements. If you select I/O Paths and Minimum TPD Paths, the Fitter works to meet the following criteria:
- Hold times (tH) from the device input pins to the registers
- Minimum delays from I/O pins to I/O registers or from I/O registers to I/O pins
- Minimum clock-to-out time (tCO) from registers to output pins
If you select All Paths, the Fitter also works to meet hold requirements from registers to registers, as highlighted in blue in the figure, in which a derived clock generated with logic causes a hold time problem on another register.
However, if your design still has internal hold time violations between registers, you can manually add delays by instantiating LCELL primitives, or by making changes to your design, such as using a clock enable signal instead of a derived or gated clock.