did you see the picture I posted in my above reply?
when you export the 's2' port to my nios II qsys top level, you will get
.dpram_s2_address(exchange_addr), // dpram_s2.address
.dpram_clk2_clk(CLK_100M), // dpram_clk2.clk
.dpram_s2_chipselect(1'b1), // .chipselect
.dpram_s2_clken(1'b1), // .clken
.dpram_s2_readdata(exchange_rdata), // .readdata
.dpram_s2_write(exchange_wren), // .write
.dpram_s2_writedata(exchange_wdata), // .writedata
then you can write or read directly to the Dual Port RAM no other timing logic needed , only pay attention that 'exchagne_wren' must be set to 1'b1 when write data is needed. 'chipselect' and 'clken' must also be set with 1'b1.
keep contact with me if there is futher problem with this issue. good luck!