SVF files can be created from ".isc" files for any device using iMPACT. The resulting SVF file for the Spartan-3A device does not play properly. The ".isc" files are used for 1532 style programming. Third-party programmers can either read in the 1532 BSDL file and ISC file, or they can read in SVF files.
The ".isc" files can be used instead of ".bit" files as the source for SVF files to alter the shift size used in the SDR command. SVF files created from ".bit" files contain one large SDR command which comprises the entire ".bit file". SVF files created from ".isc" files contain multiple 16-bit shifts. The filesare larger andtake longer to play, but havenatural break points which can help when third-party players are parsing the files.
Spartan-3A devices cannot be transitioned to a Pause-DR state during an SDR command where the ".bit" file is being shifted in. Because of this limitation, it is typically best to use 1532 style shifts when playing SVF filesfrom a third-party player. Some third-party playersneed to move the TAP controller to the Pause state while buffering the data.
This problem is due to an issue with state transitions defined by the tools.
To work around this problem, set the following environment variable:
Then, create SVF files from the ".bit" file (not the ".isc" file). This creates an SVF file with an ISC Program command and multiple smaller shift states. The resulting SVF file has the same SDR shifts defined as when the ".isc" file was used, but the state transitionsare different.