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raw_mac: Implement MAC without header field en-/decoding (only CRC + framing)

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Markus Koch 2024-07-15 13:37:42 +02:00
parent 7379df7b74
commit f57b0b1054
3 changed files with 221 additions and 1 deletions
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2
README.MD
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@ -5,7 +5,7 @@
Trashernet is a very trashy Ethernet stack for FPGAs written in VHDL aiming to cover all OSI layers:
* Layer 1, Physical: `trashernet_phy`
* Layer 2, Data link: `trashernet_mac`, `trashernet_eth`, `trashernet_arp`
* Layer 2, Data link: `trashernet_mac` (`trashernet_raw_mac`), `trashernet_eth`, `trashernet_arp`
* Layer 3, Network: `trashernet_ipv4`, `trashernet_ipv4prot`, `trashernet_icmp`
When writing it, the following were the main design philosophies:

15
trashernet/trashernet_pkg.vhd
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@ -79,6 +79,21 @@ package trashernet_pkg is
rx_mac_crc_error : std_logic; -- End of packet, CRC invalid
end record mac_out_t;
-- Raw MAC interface
type raw_mac_in_t is record
tx_mac_data : byte; -- Payload
tx_mac_data_en : std_logic; -- Start (and keep) transmitting a frame
end record raw_mac_in_t;
type raw_mac_out_t is record
rx_mac_data : byte; -- Ethernet data (after Ethertype)
rx_mac_valid : std_logic; -- `rx_mac` values (headers + data) are valid
tx_mac_data_ack : std_logic; -- The byte on `tx_mac_data` has been latched. Update to next word.
tx_active : std_logic; -- Transmission in progress
rx_mac_crc_ok : std_logic; -- End of packet, CRC OK (strobe independent from other rx_mac fields)
rx_mac_crc_error : std_logic; -- End of packet, CRC invalid
end record raw_mac_out_t;
-- MAC ETH interface
type ethernet_ii_protocol_t is record
ethertype : ethertype_t;

205
trashernet/trashernet_raw_mac.vhd Normal file
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@ -0,0 +1,205 @@
-- -------------------------------------------------------------------------- --
-- TRASHERNET - A Trashy Ethernet Stack for FPGAs --
-- -------------------------------------------------------------------------- --
-- trashernet_raw_mac.vhd : Ethernet OSI Layer 2, Data Link
-- Implements packet handling for sync header + CRC.
-- -------------------------------------------------------------------------- --
-- Author : Markus Koch <markus@notsyncing.net>
-- Contributors : None
-- License : Mozilla Public License (MPL) Version 2
-- -------------------------------------------------------------------------- --
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use work.trashernet_pkg.all;
entity trashernet_raw_mac is
port(
-- Global
clk : in std_logic; -- Global clock
rst : in std_logic; -- Asynchronous reset
-- PHY signals
phy_out : in phy_out_t; -- PHY application IF (out of PHY)
phy_in : out phy_in_t; -- PHY application IF (into PHY)
-- MAC application IF
mac_out : out raw_mac_out_t; -- MAC application IF (out of MAC)
mac_in : in raw_mac_in_t -- MAC application IF (into MAC)
);
end entity trashernet_raw_mac;
architecture rtl of trashernet_raw_mac is
constant ETH_POLYNOMIAL : std_logic_vector(31 downto 0) := x"04C11DB7";
constant ETH_FRAME_MIN_LENGTH : integer := 64;
begin
rx : block
constant CRC_LENGTH : integer := 4;
signal sr_head : byte_vector(0 to CRC_LENGTH - 1);
constant BYTE_COUNT_MAX : integer := CRC_LENGTH;
signal byte_count : integer range 0 to BYTE_COUNT_MAX;
signal sr_payload : byte_vector(0 to 4);
signal crc : std_logic_vector(ETH_POLYNOMIAL'range);
signal crc_ok : std_logic;
signal crc_clear : std_logic;
begin
crc_inst : entity work.crc
generic map(
POLYNOMIAL => ETH_POLYNOMIAL,
START => x"FFFFFFFF",
FINAL_XOR => x"FFFFFFFF",
REVERSE_OUT => true
)
port map(
clk => clk,
rst => rst,
data => phy_out.rx_data,
data_valid => phy_out.rx_data_valid,
crc_clear => crc_clear,
crc_out => crc
);
crc_ok <= '1' when crc = x"2144DF1C" else '0';
main : process(clk, rst) is
begin
if rst then
byte_count <= 0;
mac_out.rx_mac_valid <= '0';
mac_out.rx_mac_crc_error <= '0';
mac_out.rx_mac_crc_ok <= '0';
crc_clear <= '0';
elsif rising_edge(clk) then
mac_out.rx_mac_valid <= '0';
mac_out.rx_mac_crc_error <= '0';
mac_out.rx_mac_crc_ok <= '0';
crc_clear <= '0';
if phy_out.rx_data_valid then
sr_payload <= sr_payload(sr_payload'low + 1 to sr_payload'high) & phy_out.rx_data;
if byte_count = CRC_LENGTH then
mac_out.rx_mac_valid <= '1';
else
byte_count <= byte_count + 1;
end if;
end if;
if not phy_out.rx_active then
mac_out.rx_mac_crc_ok <= crc_ok;
mac_out.rx_mac_crc_error <= not crc_ok;
end if;
if phy_out.rx_error then
mac_out.rx_mac_crc_error <= '1';
end if;
if (not phy_out.rx_active) or phy_out.rx_error then
byte_count <= 0;
crc_clear <= '1';
end if;
end if;
end process main;
mac_out.rx_mac_data <= sr_payload(0);
end block rx;
tx : block
type tx_state_t is (IDLE, DATA, PAD, TXCRC);
signal tx_state : tx_state_t;
constant SYNC_HEADER : byte_vector(0 to 7) := byte_vector'(0 to 6 => x"55", 7 => x"D5");
signal sr : byte_vector(0 to SYNC_HEADER'length - 1);
constant SR_CNT_MAX : integer := sr'high;
signal sr_cnt : integer range 0 to SR_CNT_MAX;
constant BYTE_CNT_MAX : integer := ETH_FRAME_MIN_LENGTH - 4; -- Minus four because the CRC is *after* the PAD
signal byte_cnt : integer range 0 to BYTE_CNT_MAX;
signal crc : std_logic_vector(ETH_POLYNOMIAL'range);
signal crc_clear : std_logic;
signal crc_valid : std_logic;
begin
crc_inst : entity work.crc
generic map(
POLYNOMIAL => ETH_POLYNOMIAL,
START => x"FFFFFFFF",
FINAL_XOR => x"FFFFFFFF",
REVERSE_OUT => true
)
port map(
clk => clk,
rst => rst,
data => sr(0),
data_valid => crc_valid,
crc_clear => crc_clear,
crc_out => crc
);
tx_main : process(clk, rst) is
variable more_data : std_logic;
begin
if rst then
mac_out.tx_mac_data_ack <= '0';
tx_state <= IDLE;
sr_cnt <= 0;
byte_cnt <= 0;
elsif rising_edge(clk) then
mac_out.tx_mac_data_ack <= '0';
crc_valid <= '0';
more_data := more_data and mac_in.tx_mac_data_en; -- Latch a short low-pulse on tx_en
if phy_out.tx_data_ack then
sr <= sr(sr'low + 1 to sr'high) & x"00";
if sr_cnt /= 0 then
sr_cnt <= sr_cnt - 1;
end if;
if byte_cnt /= 0 then
byte_cnt <= byte_cnt - 1;
end if;
end if;
case tx_state is
when IDLE => -- Idle + prepare sync header
if not phy_out.tx_active and mac_in.tx_mac_data_en then
more_data := '1';
sr(SYNC_HEADER'range) <= SYNC_HEADER;
sr_cnt <= 7;
tx_state <= DATA;
end if;
when DATA => -- Wait for MAC header + transmit payload until tx_mac_data_en goes away
if (phy_out.tx_data_ack = '1') and (sr_cnt = 0) then -- MAC Header TX complete
if more_data then
sr(0) <= mac_in.tx_mac_data;
crc_valid <= '1';
mac_out.tx_mac_data_ack <= '1';
else
tx_state <= PAD;
end if;
end if;
when PAD => -- Wait for PADs / last payload byte + prepare CRC
if (byte_cnt = 0) then
sr(0 to 3) <= (crc(7 downto 0), crc(15 downto 8), crc(23 downto 16), crc(31 downto 24));
sr_cnt <= 4 - 1;
tx_state <= TXCRC;
end if;
when TXCRC => -- Wait for CRC + jump back to idle
if (phy_out.tx_data_ack = '1') and (sr_cnt = 0) then -- CRC TX complete
tx_state <= IDLE;
end if;
end case;
end if;
end process tx_main;
phy_in.tx_data_en <= '1' when tx_state /= IDLE else '0';
crc_clear <= '1' when sr_cnt /= 0 else '0'; -- todo: this might be to early
phy_in.tx_data <= sr(sr'low);
mac_out.tx_active <= phy_out.tx_active;
end block tx;
end architecture rtl;