How to make sure nios send a single cycle control signal to peripheral?

hye everyone..this is a very basic question

i was testing how to control custom HW using nios. The custom HW in my case is just a simple counter.

ive attach my counter to avalon bus and manage to give signal and read output from it. however a single control signal from nios triggered a few counts on my counter.

e.g :

if i do this in c

printf("count=%d",IORD_8DIRECT(COUNTER_0_BASE,1));
IOWR_8DIRECT(COUNTER_0_BASE,0,1);
printf("count=%d",IORD_8DIRECT(COUNTER_0_BASE,1));

the output is:

0
3

but i actually want it to count up a single value each time the nios tell it to.

this is my current interface for counter<->avalonbus:

module avalon_counter(
    //avalon signal
    clk,
    reset_n,
    read,
    write,
    readdata,
    writedata,
    address,
    chipselect,
    
    //conduit
    outCNT
);
input    clk,
        read,
        write,
        chipselect,
        reset_n;
        
input    address;
                
input        writedata;
output    reg        readdata;
//component signal
reg        cnt_up;
reg        cnt_dwn;
wire        oCNT;
//conduit signal
output        outCNT;
assign    outCNT = oCNT;
always@(posedge clk)
begin
    if(!reset_n)
        readdata <= 8'b0;
    else
    begin
        if (chipselect == 1'b1)
        begin
            case(address)
            1'b0: 
            begin
                if(writedata)
                begin
                    cnt_up<=1'b1;
                    cnt_dwn<=1'b0;
                end
                else
                begin
                    cnt_up<=1'b0;
                    cnt_dwn<=1'b1;
                end
            end
            1'b1:
                readdata<={2'b00,oCNT};
            endcase
        end
        else
        begin
            cnt_up <= 1'b0;
            cnt_dwn<= 1'b0;
        end    
    end
end
counter    u1(
    .clk(clk),
    .resetn(reset_n),
    .cnt_up(cnt_up),
    .cnt_dwn(cnt_dwn),
    .oCNT(oCNT)
);
endmodule

i suspect that avalon only deassert chipselect after few cycle.so as long as the chipselect==1 cnt_up or cnt_dwn is always assert with value=1.

How can i make sure that a single command from nios only trigger a single count on my counter?