Using the UDP interface.txt

Here's how to use the UDP interface.

General setup
=============
In the top level design, set the MAC address, IP address, netmask and gateway:

Here is an example for a MAC & IP setup (for 10.0.0.10/24, gw 10.0.0.254
)
    -- NOTE this is 02:23:45:67:89:AB
    constant our_mac     : std_logic_vector(47 downto 0) := x"AB_89_67_45_23_02"; 
    -- NOTE octets are reversed 
    constant our_ip      : std_logic_vector(31 downto 0) := x"0A_00_00_0A";       
    constant our_netmask : std_logic_vector(31 downto 0) := x"00_FF_FF_FF";       
    constant our_gateway : std_logic_vector(31 downto 0) := x"FE_00_00_0A";       

Transmitting UDP packets
========================
(see example in hdl/udp/udp_test_source.vhd)
0. (not yet written) Resolve the target IP address into a MAC address using 
   the ARP resolver.

1. Wait until 'udp_tx_busy' is zero

2. Provide the target MAC, source and destination ports and destination IP address, 
   and first byte of data to the udp_tx interface, and assert udp_tx_valid.

   Here is an example, of broadcasting to 10.0.0.255. Note the ordering of the 
   octets in the IP address:

     udp_tx_valid <= '1';
     udp_tx_src_port <= std_logic_vector(to_unsigned(4660,16));
     udp_tx_dst_mac  <= x"FF_FF_FF_FF_FF_FF";
     udp_tx_dst_ip   <= x"FF_00_00_0A";
     udp_tx_dst_port <= std_logic_vector(to_unsigned(9029,16));
     udp_tx_data     <= x"FF";
   
3. Provide additional data bytes on contiguious cycles. When udp_tx_valid drops it is
   considered the end of the packet. Do not send more than 1472 bytes at a time.

4. Go back to step 1 to send the next packet.

Receiving UDP packets
=====================
(see example in hdl/udp/udp_test_sink.vhd)

1. Wait for 'udp_rx_valid' to be asserted.

2. Check for your desired UDP port number on 'udp_rx_dst_port'

2. Data will be on 'udp_rx_data' while 'udp_rx_valid' is asserted.

   Here is an example, of recieving on port 4660.

    if udp_rx_valid = '1' then
        if udp_rx_dst_port = std_logic_vector(to_unsigned(4660, 16)) then  
            leds <= udp_rx_data;
        end if;
    end if;