Is there a minimum frequency limitation for MicroBlaze?
MicroBlaze is a fully synchronized design except for the debug logic which runs on its own JTAG clock. If you do not use the debug logic, MicroBlaze can run as low as you like down to 1 Hz. But if you use the debug logic, there are signals that are transferred between the debug clock region and MicroBlaze clock region. This design assumes that MicroBlaze is running faster than the debug clock. So if MicroBlaze is using debug, the minimum clock frequency is the debug clock.