Why does the Nios II processor generate incorrect results from shift right (SRAI, SRA) operations?

Description

Using the Quartus® II software version 12.0 and earlier, shift right operations by Nios® II processor on Arria® V and Stratix® V devices may produce incorrect results when ‘DSP Block’ is selected as hardware multiplication type.  If the Nios II processor executes the SRAI or SRA instruction on a negative value, the result is shifted but will not be sign extended.

Resolution

This issue is caused by changes to the wrapper for the DSP blocks for 28nm devices where the SRAI and SRA instructions do not sign extend shifted results.

To fix this issue in Quartus II 12.0, please obtain the patch by filing a service request in mySupport and reference this solution number.

The bug will be fixed in Quartus II software version 12.0 SP1.