Can On-Chip Memory (OCM) run as fast as the cache array in the PowerPC CPU?
In most cases, the answer is no. Unlike the IBM PPC405GP ASIC chip, the On-Chip Memory in Virtex-II Pro is implemented with BRAMs in the FPGA fabric. The speed of OCM depends upon numbers of BRAMs. In most cases, the OCM clocks are not as fast as the CPU clock; that is, the speed of OCM is not as fast as cache array. For information on how to determine the clock speed for OCM, refer to (Xilinx Answer 16324).