When using the DDR3 UniPHY quarter rate controller, you may notice that avl_ready goes low immediately following a read or write request. This leads to poor read and write efficiency by the controller.
There is a known issue with the quarter rate controller where it de-asserts avl_ready following a burst command with a burst size larger than one. The controller de-asserts avl_ready for one cycle stalling the Avalon command queue.
The workaround is to use a burst size of one to achieve maximum efficiency or to use a larger burst size, such as 32 or 64, to minimize the effect of the one cycle stall.
This issue will be fixed in a future version of the Quartus® II software.