chemeris/UHD-Fairwaves — comment on commit 18f19a044f61ee2491ccd3b4a756538d24228160
File: fpga/usrp2/control_lib/s3a_icap_wb.v line 76
By closehaulcom:

Just because cascading DCMs can work in some circumstances, it is still generally a bad idea and should only be done if there's absolutely no other reasonable choice. Scroll down to "Cascading DCMs" in the link below):
http://www.xilinx.com/support/troubleshoot/clocking_debug.htm