Why doesn't read data return as expected from an Avalon-MM slave ?

Description

Due to a problem in the Quartus® II software version 12.1 and earlier, read data may not return as expected when the Avalon-MM master's data port bit width is wider than the Avalon-MM slave's port bit width (for example: master bit width=64 bits, slave bit width=32 bits) and the Maximum pending read transactions parameter on the Avalon-MM Master is greater than 1.

Resolution

To work around this problem, set the same bit-width on both the master and slave port, or set the Maximum pending read transactions parameter to 1 on Avalon-MM master.

This problem is scheduled to be fixed in a future release of the Quartus II software.