Lattice iCECube2: Why does my Constraints for the output of Oscillators in iCECube2 is ignored by the tool?
Description:
iCEcube2 only allows an inferred constraint on the internal OSC at its nominal value and Timing Analysis can't be set to a different frequency for the OSC as the user constraint will be ignored.
Solution:
This can work be around by feeding the output of the oscillator to a PLL (where the PLL is in 1:1 mode, i.e., 48 MHz input and 48 MHz output), then adding a constraint to overconstrain the output of the PLL to 52.8 MHz to cover the 10% tolerance of the OSC.