Simple code example where the IOP16B reads the pushbutton and writes to the LED on the FPGA card. 

Sources

• Application VHDL code is here.
• IOP16B VHDL code is here.
• Assembly code is here.
• Some other VHDL pieces are in subdirectories from here.

Memory Map

Single peripheral address (0x00), data bit (D0).

Top Level Entity

entity TestIOP16B is
  port (
    -- Clock and reset
    i_clk      : in std_logic := '1';   -- Clock (50 MHz)
    i_n_reset  : in std_logic := '1';
    -- The key and LED on the FPGA card
    i_key1      : in std_logic := '1';  -- KEY1 on the FPGA card
    o_UsrLed    : out std_logic := '1'  -- USR LED on the FPGA card
  );
end TestIOP16B;

CPU Instance

IOP16: ENTITY work.IOP16
-- Need to pass down instruction RAM and stack sizes
  generic map     ( 
    INST_SRAM_SIZE_PASS  => 512,  -- Small code size since program is "simple"
    STACK_DEPTH_PASS     => 4     -- Single level subroutine (not nested)
  )
  PORT map (
    i_clk             => i_clk,
    i_resetN          => w_resetClean_n,
    -- Peripheral bus signals
    i_periphDataIn    => w_periphIn,
    o_periphWr        => w_periphWr,
    o_periphRd        => w_periphRd,
    o_periphDataOut   => w_periphOut,
    o_periphAdr       => w_periphAdr
  );

Code

List file is:

000    SELF    0x6000    IOR    0x00    IO_00    read pushbutton
001            0x7000    IOW    0x00    IO_00    write LED
002            0xE000    JMP    SELF                    

 IOP_ROM

The ROM file name has to be IOP_ROM and it gets stored in the current project folder. That allows for the IOP16B to be used in other projects. The Assembler creates a MIF file which gas to be loaded:

IOP_ROM

The IOP_ROM instance has two parameters: INST_SRAM_SIZE_PASS and STACK_DEPTH_PASS.

-- Set stack size in STACK_DEPTH generic
IOP16: ENTITY work.IOP16
-- Need to pass down instruction RAM and stack sizes
  generic map {
    INST_SRAM_SIZE_PASS => 512,  -- Small code size since program is "simple"
    STACK_DEPTH_PASS    => 1     -- Single level subroutine (not nested)
)

 INST_SRAM_SIZE_PASS has to match the size of the IOP_ROM.

STACK_DEPTH_PASS can be 0, 1, or > 1 (typically 4 for 16) deep stack,

Application Example Logic

-- Peripheral bus read mux

w_periphIn <= "0000000"&i_key1 when (w_periphAdr=x"00") else
              x"00";

-- Strobes/Selects
w_wrLED <= '1' when ((w_periphAdr=x"00") and (w_periphWr = '1')) else '0';

latchLED: PROCESS (i_clk)
BEGIN
  IF rising_edge(i_clk) THEN
    if w_wrLED = '1' then
      o_UsrLed <= w_periphOut(0);
    END IF;
  END IF;
END PROCESS;