On page 23 of the Xilinx Application Note "Virtex FPGA Series Configuration and Readback" (Xilinx XAPP138), the equation given for calculating the bit position in the readback data is incorrect, given the ".ll" file, in versions 1.0 - 2.0.
The correct equation for Virtex/Virtex-E is as follows (it also appears in the current version of XAPP138):
Readback Bit Number = Frame Number * Frame Length + Bitmap Length - Frame Offset + 32
For 3.1i software, this equation was required to calculate the location of data in the readback bit streams from the logic allocation file (".ll"):
The Bitmap Length is different for each Virtex device, and is listed in Table 16 of XAPP138.
For 4.1i software, the logic allocation file was adjusted to give exact positioning of data in the readback bitstream:
- The first number less 32 is the absolute bit position. This issue is resolved in 5.1i and later.
- The second number is the frame address (in hex).
- The third number is the bit offset within the frame.
For 5.1i software and later, the logic allocation file was adjusted to give exact positioning of data in the readback bit stream:
For Virtex-E parts, the lengths are:
V50E - 324
V150E - 468
V200E - 540
V300E - 612
V400E - 756
V600E - 900
V812E - 1044
V1000E - 1188
V1600E - 1332
V2000E - 1476
V2600E - 1692
V3200E - 1908