ME235 Laboratory 8 Switching Control and Computer Interfacing, a.k.a Design of Embedded Systems

SHARC/Xilinx bus interface

The purpose of this lab is to build an interface between the SHARC board and the Xilinx part that will allow you to read and write registers in the Xilinx part from C code running on the SHARC board.

• REMEMBER FOR THIS LAB
  1. Use an external reset signal connected to a slide switch on the Xilinx board.
  2. Always use a synthesizable form for your VHDL:

         process(clk, reset)
         begin
             if reset = '0' then
     	        -- reset logic is here.
             elsif rising_edge(clk)
                 -- sequential logic is here.
             end if;
         end process;
     

  3. Write your VHDL in small processes, not in a single large process.
  4. Sequential logic will not be fast enough to control the tri-state for the data bus and the acknowledge. This will have to be done in combinational logic.
  
  
  
• DESIGN THE XILINX SIDE OF THE SYSTEM

  Use the Xilinx to provide 8, 8-bit registers.

  These registers will be read/write registers, so they must be connected to INOUT pins on the Xilinx.

  Connect three input pins on the Xilinx for address.

  Connect the read and write signals of the bus to input pins on the Xilinx.

  Use the read and chip select signals to control the output enable for the data bus.

  Use the write signal and the decoded address to control writing to the eight registers.

  Create a simple countdown clock to generate the acknowledge signal from the time the chip select goes true. This time should can be relatively long (perhaps 1 microsecond) because of our long bus wires.
  
  

• SIMULATE THE SYSTEM

  In particular, make sure that the timing for the chip select, read, write, and acknowledge are correct.
  
  

• CONNECT THE BOARDS TOGETHER AND TEST

  You should now be able to write a C program on the DSP that will read and write values to and from these registers. Make sure that Memory Segment 2 is configured to require an acknowledge. If the DSP hangs during your program, go back to basics and make sure that you can read on-board inputs and write on-board outputs. Then, watch the MS2 chip select and the acknowledge. If the Xilinx part does not drive the acknowledge, the SHARC will hang forever waiting for it.
  
  

• LAB REPORT

  Turn in the VHDL for the Xilinx program and the C code for the DSP.