From f48a1fad1d73ac7f569e6c50c31592dd486bf8b9 Mon Sep 17 00:00:00 2001
From: Reinier van der Walle <walle@astron.nl>
Date: Fri, 21 Jul 2017 06:48:36 +0000
Subject: [PATCH] added comments
---
.../io/eth/src/vhdl/eth_checksum_10g.vhd | 103 ++++++++++--------
1 file changed, 58 insertions(+), 45 deletions(-)
diff --git a/libraries/io/eth/src/vhdl/eth_checksum_10g.vhd b/libraries/io/eth/src/vhdl/eth_checksum_10g.vhd
index 17ba139d8a..0b6b283935 100644
--- a/libraries/io/eth/src/vhdl/eth_checksum_10g.vhd
+++ b/libraries/io/eth/src/vhdl/eth_checksum_10g.vhd
@@ -25,26 +25,15 @@ USE IEEE.std_logic_1164.ALL;
USE IEEE.numeric_std.ALL;
USE common_lib.common_pkg.ALL;
USE dp_lib.dp_stream_pkg.ALL;
-
--- Purpose:
--- Can be used to calculate the checksum for IPv4, ICMP and UDP, provided
--- the correct words are provided between sop and eop.
--- Description:
--- Determine the 16 bit 1-complement checksum according IPv4 to for the valid
--- words between snk_in.sop and snk_in.eop, taking in account snk_in.empty.
--- . For checksum verification the result should be 0 when the words are OK.
--- . For checksum calculation the result should be used at the checksum field
--- in the packet header.
--- Remarks:
--- . At the snk_in.sop the checksum is initialized to 0.
--- . At the snk_in.eop the snk_in.empty LSBytes are padded with 0.
--- . The words do not need to be provided in order, because the checksum is
--- based on addition.
--- . Assume that snk_in.sop and snk_in.eop are only active when snk_in.valid
--- is active.
--- . Assume that between packets so from snk_in.eop to next snk_in.sop the
--- snk_in.valid is inactive and that snk_in.valid is only active for new
--- data.
+----------------------------------------------------------------------------------
+-- Purpose: --
+-- Can be used to calculate and insert the checksum for the IP header --
+-- in a 10GbE package, if the correct longwords are provided. --
+-- Description: --
+-- Determine the 16 bit 1-complement checksum according IPv4 to for the valid --
+-- words between snk_in.sop and the last ip header field. --
+-- After calculation, the checksum is inserted in the outgoing stream --
+----------------------------------------------------------------------------------
ENTITY eth_checksum_10g IS
PORT (
@@ -61,23 +50,24 @@ END eth_checksum_10g;
ARCHITECTURE rtl OF eth_checksum_10g IS
- CONSTANT c_cin_w : NATURAL := 4; --true_log2(c_nof_half_words - 1);
+ CONSTANT c_cin_w : NATURAL := 4; --bit width of carry
CONSTANT c_pipeline_delay : NATURAL := 2;
- SIGNAL sum : UNSIGNED(c_halfword_w + c_cin_w -1 DOWNTO 0) := (OTHERS => '0');
- SIGNAL checksum : STD_LOGIC_VECTOR(c_halfword_w-1 DOWNTO 0);
+ SIGNAL sum : UNSIGNED(c_halfword_w + c_cin_w -1 DOWNTO 0) := (OTHERS => '0');
+ SIGNAL checksum : STD_LOGIC_VECTOR(c_halfword_w-1 DOWNTO 0);
+ SIGNAL cnt_clr, cnt_p_clr : STD_LOGIC;
+ SIGNAL cnt_en, cnt_p_en : STD_LOGIC;
+ SIGNAL count, count_p : STD_LOGIC_VECTOR(31 DOWNTO 0);
SIGNAL dp_pipeline_src_out : t_dp_sosi;
- SIGNAL cnt_clr : STD_LOGIC;
- SIGNAL cnt_en : STD_LOGIC;
- SIGNAL count : STD_LOGIC_VECTOR(31 DOWNTO 0);
-
BEGIN
+ -------------------------------------------------
+ -- process to calculate the ip_header_checksum --
+ -------------------------------------------------
p_calc_chksum : PROCESS(clk)
BEGIN
IF rst = '1' THEN
sum <= (OTHERS => '0');
- --checksum <= (OTHERS => '0');
ELSIF RISING_EDGE(clk) THEN
IF cnt_clr = '1' THEN
@@ -85,37 +75,43 @@ BEGIN
ELSIF cnt_en = '1' THEN
CASE TO_UINT(count) IS
- WHEN 0 =>
- sum <= sum + UNSIGNED(snk_in.data(c_halfword_w-1 DOWNTO 0));
+ WHEN 0 => -- 0 is the cycle after the sop due to the common_counter latency
+ sum <= sum + UNSIGNED(snk_in.data(c_halfword_w-1 DOWNTO 0)); -- ip_version, ip_header_length, ip_services
WHEN 1 =>
- sum <= sum + UNSIGNED(snk_in.data(c_halfword_w*4 -1 DOWNTO c_halfword_w *3))
- + UNSIGNED(snk_in.data(c_halfword_w*3 -1 DOWNTO c_halfword_w *2))
- + UNSIGNED(snk_in.data(c_halfword_w*2 -1 DOWNTO c_halfword_w))
- + UNSIGNED(snk_in.data(c_halfword_w -1 DOWNTO 0));
- WHEN 2 =>
- sum <= sum + UNSIGNED(snk_in.data(c_halfword_w*3 -1 DOWNTO c_halfword_w *2))
- + UNSIGNED(snk_in.data(c_halfword_w*2 -1 DOWNTO c_halfword_w))
- + UNSIGNED(snk_in.data(c_halfword_w -1 DOWNTO 0));
+ sum <= sum + UNSIGNED(snk_in.data(c_halfword_w*4 -1 DOWNTO c_halfword_w *3)) -- ip_total_length
+ + UNSIGNED(snk_in.data(c_halfword_w*3 -1 DOWNTO c_halfword_w *2)) -- ip_identification
+ + UNSIGNED(snk_in.data(c_halfword_w*2 -1 DOWNTO c_halfword_w)) -- ip_flags, ip_fragment_offset
+ + UNSIGNED(snk_in.data(c_halfword_w -1 DOWNTO 0)); -- ip_time_to_live, ip_protocol
+ WHEN 2 => -- skip ip_header_checksum
+ sum <= sum + UNSIGNED(snk_in.data(c_halfword_w*3 -1 DOWNTO c_halfword_w *2)) -- ip_src_addr(1/2)
+ + UNSIGNED(snk_in.data(c_halfword_w*2 -1 DOWNTO c_halfword_w)) -- ip_src_addr(2/2)
+ + UNSIGNED(snk_in.data(c_halfword_w -1 DOWNTO 0)); -- ip_dst_addr(1/2)
WHEN 3 =>
- sum <= sum + UNSIGNED(snk_in.data(c_halfword_w*4 -1 DOWNTO c_halfword_w *3));
+ sum <= sum + UNSIGNED(snk_in.data(c_halfword_w*4 -1 DOWNTO c_halfword_w *3));-- ip_dst_addr(2/2)
WHEN OTHERS =>
END CASE;
END IF;
END IF;
- END PROCESS;
+ END PROCESS;
- checksum <= NOT(STD_LOGIC_VECTOR(sum(c_halfword_w-1 DOWNTO 0)+sum(sum'HIGH DOWNTO c_halfword_w)));
+ ---------------------------------------------------
+ -- process to insert checksum in outgoing stream --
+ ---------------------------------------------------
+ checksum <= NOT(STD_LOGIC_VECTOR(sum(c_halfword_w-1 DOWNTO 0)+sum(sum'HIGH DOWNTO c_halfword_w))); -- checksum = inverted (sum + carry)
p_insert_chksum : PROCESS(dp_pipeline_src_out, checksum, count)
BEGIN
src_out <= dp_pipeline_src_out;
- IF TO_UINT(count) = 2+c_pipeline_delay THEN
+ IF TO_UINT(count_p) = 2 THEN
src_out.data(c_halfword_w*4 -1 DOWNTO c_halfword_w *3) <= checksum;
END IF;
END PROCESS;
- cnt_en <= snk_in.valid;
- cnt_clr <= snk_in.sop;
+ -------------------------------------------------------------------------------------------
+ -- useing common_counter to keep track of the word alignment during checksum calculation --
+ -------------------------------------------------------------------------------------------
+ cnt_en <= snk_in.valid; -- only count when valid
+ cnt_clr <= snk_in.sop; -- restart counter on sop
u_calc_counter : ENTITY common_lib.common_counter
PORT MAP (
@@ -124,8 +120,25 @@ BEGIN
cnt_clr => cnt_clr,
cnt_en => cnt_en,
count => count
- );
+ );
+ -----------------------------------------------------------------------------------------
+ -- useing common_counter to keep track of the word alignment during checksum insertion --
+ -----------------------------------------------------------------------------------------
+ cnt_p_en <= dp_pipeline_src_out.valid; -- only count when valid
+ cnt_p_clr <= dp_pipeline_src_out.sop; -- restart counter on sop
+
+ u_pipe_counter : ENTITY common_lib.common_counter
+ PORT MAP (
+ rst => rst,
+ clk => clk,
+ cnt_clr => cnt_p_clr,
+ cnt_en => cnt_p_en,
+ count => count_p
+ );
+ --------------------------------------------------------------------------------
+ -- useing dp_pipeline to make room for the checksum calculation and insertion --
+ --------------------------------------------------------------------------------
u_dp_pipeline : ENTITY dp_lib.dp_pipeline
GENERIC MAP (
g_pipeline => c_pipeline_delay
--
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