Custom Instruction accessing SDRAM

Hello

I am currently trying to update a memory location content inside SDRAM from a custom instruction(function called from nios ii). From what I understand, I need to use avalon memory mapped interfaces.

tried the following implementation below, but would not get it to work. is there something that I missed out or misinterpreted?

inside QSYS the custom instruction having a MM master connected to SDRAM MM slave, and for the custom instruction side, a template for avalon mm simple master is being added with a portion of the codes included for custom instruction.

//avalon MM Master port
    input clock, reset;
    output reg avalon_master_address;
    output avalon_master_byteenable;
    output reg avalon_master_read;
    input avalon_master_readdata;
    input avalon_master_response;
    input avalon_master_waitrequest; //not used
    output reg avalon_master_write;
    output reg avalon_master_writedata;
    assign avalon_master_byteenable = 4'b1111;
    always@(posedge clk)
    begin
            if(clk_en)
            begin
                if(start)
                begin
                    case(n)
                    2 :    begin
                            avalon_master_address <= addressA;
                            avalon_master_writedata <= dataB;
                            avalon_master_read <= 1'b0;
                            avalon_master_write <= 1'b1;
                            if(avalon_master_response == 2'b00)
                                n2_done <= 1'b1;
                        end
                end
            end
        end
    end

Thanks in advance