You may see this behavior with the Quartus® II software versions 9.1 and earlier when an MLAB is configured without a clock enable, and the LUTRAM does not share the same clock routing as its Datain registers. This condition triggers an Assembler problem that grounds the clock enable of LUTRAM and causes the MLAB to be always disabled for write operations. This error may impact designs targeting Stratix® III, Stratix IV, and Arria® II GX device families.
If your design was compiled with Quartus II software versions 9.1 or earlier, and has run successfully in hardware, it should indicate that the Assembler bug is not triggered and the MLAB failure will not be seen.
A patch is available to fix this problem for the Quartus II software version 9.1. Download and install Patch 0.59 from the appropriate link below and recompile your design.
- Download the Quartus II software version 9.1 Patch 0.59 for Windows (.exe)
- Download the Readme for the Quartus II software version 9.1 Patch 0.59 for Windows (.txt)
- Download the Quartus II software version 9.1 Patch 0.59 for Linux (.tar)
- Download the Readme for the Quartus II software version 9.1 Patch 0.59 for Linux (.txt)
This problem is scheduled to be fixed in a future version of the Quartus II software.