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Development System Reference Guide www.xilinx.com 275
BitGen Options
R
–l (Create a Logic Allocation File)
This option creates an ASCII logic allocation file (design.ll) for the selected design. The logic
allocation file shows the bitstream position of latches, flip-flops, IOB inputs and outputs,
and the bitstream position of LUT programming and Block RAMs.
In some applications, you may want to observe the contents of the FPGA internal registers
at different times. The file created by the –l option helps you identify which bits in the
current bitstream represent outputs of flip-flops and latches. Bits are referenced by frame
and bit number within the frame.
The iMPACT tool uses the design.ll file to locate signal values inside a readback bitstream.
–m (Generate a Mask File)
Creates a mask file. This file determines which bits in the bitstream should be compared to
readback data for verification purposes.
–r (Create a Partial Bit File)
–r bit_file
The –r option is used to create a partial bit file. It takes that bit file and compares it to the
.ncd file given to bitgen. Instead of writing out a full bit file, it only writes out the part of
the bit file that is different from the original bit file given.
–w (Overwrite Existing Output File)
Enables you to overwrite an existing BitGen output file. See “BitGen Output Files” for
additional information.