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White Rabbit core collection
Commit b2e82e93 authored by Wesley W. Terpstra's avatar Wesley W. Terpstra
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gtp_bitslide: fix unsafe clock crossings 

The bitslide state machine was asynchronously released from reset
and also used serdes_ready_i in state transitions. Both are unsafe.
parent fd76aee4
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platform/xilinx/wr_gtp_phy/gtp_bitslide.vhd
View file @ b2e82e93
......@@ -101,102 +101,100 @@ architecture behavioral of gtp_bitslide is
type t_bitslide_fsm_state is (S_SYNC_LOST, S_STABILIZE, S_SLIDE, S_PAUSE, S_GOT_SYNC, S_RESET_CDR);
signal cur_slide : unsigned(4 downto 0);
signal state : t_bitslide_fsm_state;
signal counter : unsigned(15 downto 0);
signal state : t_bitslide_fsm_state;
signal counter : unsigned(15 downto 0);
signal commas_missed : unsigned(4 downto 0);
signal cur_slide : unsigned(4 downto 0);
signal slide_rst : std_logic_vector(2 downto 0) := (others => '1');
begin -- behavioral
p_do_slide : process(gtp_rx_clk_i, gtp_rst_i)
p_do_slide : process(gtp_rx_clk_i)
begin
if gtp_rst_i = '1' then
state <= S_SYNC_LOST;
gtp_rx_slide_o <= '0';
counter <= (others => '0');
synced_o <= '0';
gtp_rx_cdr_rst_o <= '0';
elsif rising_edge(gtp_rx_clk_i) then
if rising_edge(gtp_rx_clk_i) then
-- Safely synchronize reset conditions
slide_rst <= (gtp_rst_i or not serdes_ready_i) &
slide_rst(slide_rst'left downto 1);
if(serdes_ready_i = '0') then
state <= S_SYNC_LOST;
end if;
case state is
-- State: synchronization lost. Waits until a comma pattern is detected
when S_SYNC_LOST =>
cur_slide <= (others => '0');
counter <= (others => '0');
gtp_rx_slide_o <= '0';
synced_o <= '0';
gtp_rx_cdr_rst_o <= '0';
commas_missed <= (others => '0');
if(gtp_rx_comma_det_i = '1') then
state <= S_STABILIZE;
end if;
-- State: stabilize:
when S_STABILIZE =>
if(gtp_rx_comma_det_i = '1') then
counter <= counter + 1;
commas_missed <= (others => '0');
else
commas_missed <= commas_missed + 1;
if(commas_missed(3) = '1') then
state <= S_SYNC_LOST;
if slide_rst(0) = '1' then
state <= S_SYNC_LOST;
counter <= (others => '0');
commas_missed <= (others => '0');
cur_slide <= (others => '0');
bitslide_o <= (others => '0');
gtp_rx_slide_o <= '0';
synced_o <= '0';
gtp_rx_cdr_rst_o <= '0';
else
case state is
-- State: synchronization lost. Waits until a comma pattern is detected
when S_SYNC_LOST =>
counter <= (others => '0');
commas_missed <= (others => '0');
cur_slide <= (others => '0');
bitslide_o <= (others => '0');
gtp_rx_slide_o <= '0';
synced_o <= '0';
gtp_rx_cdr_rst_o <= '0';
if(gtp_rx_comma_det_i = '1') then
state <= S_STABILIZE;
end if;
end if;
if(counter = to_unsigned(c_sync_detect_threshold, counter'length)) then
counter <= (others => '0');
state <= S_PAUSE;
end if;
if(serdes_ready_i = '0') then
state <= S_SYNC_LOST;
end if;
when S_SLIDE =>
cur_slide <= cur_slide + 1;
gtp_rx_slide_o <= '1';
counter <= (others => '0');
-- State: stabilize:
when S_STABILIZE =>
if(gtp_rx_comma_det_i = '1') then
counter <= counter + 1;
commas_missed <= (others => '0');
else
commas_missed <= commas_missed + 1;
if(commas_missed(3) = '1') then
state <= S_SYNC_LOST;
end if;
end if;
state <= S_PAUSE;
if(counter = to_unsigned(c_sync_detect_threshold, counter'length)) then
counter <= (others => '0');
state <= S_PAUSE;
end if;
if(serdes_ready_i = '0') then
state <= S_SYNC_LOST;
end if;
when S_SLIDE =>
counter <= (others => '0');
cur_slide <= cur_slide + 1;
gtp_rx_slide_o <= '1';
when S_PAUSE =>
counter <= counter + 1;
gtp_rx_slide_o <= '0';
state <= S_PAUSE;
if(counter = to_unsigned(c_pause_tics, counter'length)) then
when S_PAUSE =>
counter <= counter + 1;
gtp_rx_slide_o <= '0';
if(counter = to_unsigned(c_pause_tics, counter'length)) then
if(gtp_rx_byte_is_aligned_i = '0') then
state <= S_SLIDE;
else
state <= S_GOT_SYNC;
end if;
end if;
when S_GOT_SYNC =>
gtp_rx_slide_o <= '0';
bitslide_o <= std_logic_vector(cur_slide);
synced_o <= '1';
if(gtp_rx_byte_is_aligned_i = '0') then
state <= S_SLIDE;
else
state <= S_GOT_SYNC;
gtp_rx_cdr_rst_o <= '1';
state <= S_SYNC_LOST;
end if;
end if;
when S_GOT_SYNC =>
gtp_rx_slide_o <= '0';
bitslide_o <= std_logic_vector(cur_slide);
synced_o <= '1';
if(gtp_rx_byte_is_aligned_i = '0' or serdes_ready_i = '0') then
gtp_rx_cdr_rst_o <= '1';
state <= S_SYNC_LOST;
end if;
when others => null;
end case;
when others => null;
end case;
end if;
end if;
end process;
......
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