DE2 board USB communication

I assume that you are using tmp to detect a change in buffer_full ?

if (tmp = '0') and (buffer_full = '1') then
  tmp <= '1';
  -- do your start stuff here
end if;

i know the clock process, but i dont know how to use it to check buffer_full. Can you explain more, thanks...

You need to write a clocked process and check the status of buffer_full. Don't use a while' use a if instead. If buffer_full is 0 then you don't do anything, if it is 1 then you start.

i'm trying to do DMA mode, that can read and write data, when buffer_full = '1' then it can start, my teacher said cannot use "wait until"... should i give you my whole code?

you don't have any pause in your loop, so if buffer_full is 0, then you will get stuck in the loop indefinitely.

while (tmp = '0') loop

aaaa:(, then how to do now, i'm crying la

I think that learning VHDL and use it to implement the USB protocol in two weeks is a bit optimistic, yes.

thanks, but i only have 2 weeks to finish the project, and it is too busy right?!

I think you should learn about VHDL programming first, then you try to implement simple design in FPGA. After that you move to your true project. One of recommended books to learn VHDL is Circuit Design with VHDL by Volnei A. Pedroni.