Prior to ISE Design Suite 13.2, the estimated block RAM utilization for the ChipScope Core Insertercan at times beincorrect.
For example, an ILA core with a width of 64 and depth of 1024 sample is inserted so the blockRAM size is 64x1K. Knowing this, it is expected that 4 18K block RAM should be used (64x1K/18K = 3.6 block RAM). However, the core inserter estimates only 2 in the block RAM count box. After the design is placed and routed, there is actually 4 block RAM for the ILA core (not 2).
What is the problem?
This is a knownissue for the ChipScope Inserter tool prior to the 13.2 ISE software.The BlockRAM Estimator in the Inserter tool is counting the number of RAMB36 blocks to estimate the total usage for the ILA core. Since some devices do not have RAMB36 blocks (in the case of the Spartan-6 FPGA, it uses RAMB18 blocks), the estimator might not be accurate.
This has been fixed in the ChipScope Inserter tool version 13.2 and later.