2251 - LatticeECP3:  Why only 7 out of 8 Secondary clocks can be assigned in a clock region for LatticeECP3 devices?

2251 - LatticeECP3:  Why only 7 out of 8 Secondary clocks can be assigned in a clock region for LatticeECP3 devices?

In an LatticeECP3 family of devices, only 7 out of 8 SECONDARY clocks are available. One of the SECONDARY clocks does not go to the clock input of registers in the fabric. It only goes to clock enable or set/reset pins. So, the SECONDARY clocks are not truly clock resources, but rather SECONDARY routing resources.

There are two workarounds for this:

  1. Make sure that a clock region does not contain more than 7 SECONDARY clocks. This can be achieved by assigning each clock to specific clock regions.
  2. Use PRIMARY instead of SECONDARY for the 8th clock.