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AR# 7803

Virtex Readback/ XAPP138 - Corrected equation for calculating readback bit positions


General Description:

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 Frame Number and Frame Offset are given in the ".ll" file. The Frame Length is given on page 11 of (Xilinx XAPP138).

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

AR# 7803
Date 12/15/2012
Status Active
Type General Article