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CTU CAN FD IP Core
Commit c3c508d2 authored by Ille, Ondrej, Ing.'s avatar Ille, Ondrej, Ing.
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Re-worked bit stuffing.

parent 83ba10c4
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src/can_core/bit_stuffing/bit_stuffing.vhd
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......@@ -70,12 +70,15 @@
-- bit-stuffing and thus be before in the If-elsif condition!
-- This is due to possible conflic of normal and fixed bit stuffing
-- in the start of FD CRC. Fixed bit-stuff should win!
-- 22.12.2018 Re-worked bit-stuffing to hae the logic separated to several
-- processes.
--------------------------------------------------------------------------------
Library ieee;
USE IEEE.std_logic_1164.all;
USE IEEE.numeric_std.ALL;
USE WORK.CANconstants.ALL;
use work.cmn_lib.all;
entity bit_stuffing is
port(
......@@ -129,120 +132,339 @@ end entity;
architecture rtl of bit_stuffing is
----------------------------------------------------------------------------
-- Internal Registers
----------------------------------------------------------------------------
---------------------------------------------------------------------------
-- Counter with number of equal consequent bits
---------------------------------------------------------------------------
signal same_bits : natural range 0 to 7;
signal same_bits_add : natural range 0 to 7;
signal same_bits_nxt : natural range 0 to 7;
-- Number of equal consequent bits
signal same_bits : natural range 0 to 7;
-- Value of previously transcieved bit
signal prev_bit : std_logic;
signal prev_bit : std_logic;
-- Halt for CAN Core
signal halt_reg : std_logic;
signal halt_reg : std_logic;
signal halt_reg_nxt : std_logic;
---------------------------------------------------------------------------
-- Registered value of fixed stuffing.
---------------------------------------------------------------------------
signal fixed_reg : std_logic;
signal fixed_reg_nxt : std_logic;
---------------------------------------------------------------------------
-- Counter with regularly stuffed bits
---------------------------------------------------------------------------
signal stuff_ctr : natural range 0 to 7;
signal stuff_ctr_add : natural range 0 to 7;
signal stuff_ctr_nxt : natural range 0 to 7;
---------------------------------------------------------------------------
-- Registered value of enable input
---------------------------------------------------------------------------
signal enable_prev : std_logic;
---------------------------------------------------------------------------
-- Combinational signals
---------------------------------------------------------------------------
---------------------------------------------------------------------------
-- Bit stuffing method has changed from non-fixed to fixed bit stuffing.
-- No need to assume change from fixed to non-fixed since after coding
-- CRC of CAN FD, there are no further stuff bits with non-fixed bit
-- stuffing!
---------------------------------------------------------------------------
signal non_fix_to_fix_chng : std_logic;
---------------------------------------------------------------------------
-- Signals that stuff count has reached number of same consecutive bits
-- and that stuff bit should be inserted!
---------------------------------------------------------------------------
signal stuff_lvl_reached : std_logic;
---------------------------------------------------------------------------
-- Counter of equal consecutive bits should be re-set to 1 in next
-- processed bit
---------------------------------------------------------------------------
signal same_bits_rst_trig : std_logic;
---------------------------------------------------------------------------
-- Counter of equal consecutive bits should be re-set to 1 in next clock
-- cycle.
---------------------------------------------------------------------------
signal same_bits_rst : std_logic;
---------------------------------------------------------------------------
-- Condition for insertion of stuff bit
---------------------------------------------------------------------------
signal insert_stuff_bit : std_logic;
---------------------------------------------------------------------------
-- Calculation of next data output value when circuit is enabled
---------------------------------------------------------------------------
signal data_out_nxt_ena : std_logic;
---------------------------------------------------------------------------
-- Next data output value (both when enabled and disabled)
---------------------------------------------------------------------------
signal data_out_nxt : std_logic;
---------------------------------------------------------------------------
-- Clock enable for output data register
---------------------------------------------------------------------------
signal data_out_load : std_logic;
-- Registered value of fixed stuffing
signal fixed_prev : std_logic;
begin
signal stuff_ctr : natural range 0 to 7;
signal enable_prev : std_logic;
---------------------------------------------------------------------------
-- Registering previous value of enable input to detect 0->1 transition.
---------------------------------------------------------------------------
dff_ena_reg : dff_arst
generic map(
reset_polarity => ACT_RESET,
rst_val => '0'
)
port map(
arst => res_n,
clk => clk_sys,
input => enable,
load => '1',
output => enable_prev
);
begin
bst_ctr <= stuff_ctr;
---------------------------------------------------------------------------
-- Detection of change on fixed stuff settings upon mismatch between
-- actual and registered value of fixed stuff settings from previous bit.
---------------------------------------------------------------------------
non_fix_to_fix_chng <= '1' when (fixed_stuff = '1' and fixed_reg = '0')
else
'0';
---------------------------------------------------------------------------
-- Calculation of next value in fixed stuff register:
-- 1. Re-started upon 0->1 transition on "enable"
-- 2. Store "fixed_stuff" configuration when data are processed
---------------------------------------------------------------------------
fixed_reg_nxt <= '0' when (enable_prev = '0') else
fixed_stuff when (tran_trig_1 = '1') else
fixed_reg;
---------------------------------------------------------------------------
-- Registering previous value of fixed bit stuffing to detect first
-- fixed stuff bit and insert stuff bit in the beginning of CRC for CAN FD
-- automatically!
---------------------------------------------------------------------------
dff_fixed_stuff_reg : dff_arst
generic map(
reset_polarity => ACT_RESET,
rst_val => '0'
)
port map(
arst => res_n,
clk => clk_sys,
input => fixed_reg_nxt,
load => enable,
output => fixed_reg
);
stuff_proc : process(res_n, clk_sys)
---------------------------------------------------------------------------
-- Combinationally incremented stuff counter by 1.
---------------------------------------------------------------------------
stuff_ctr_add <= (stuff_ctr + 1) mod 8;
---------------------------------------------------------------------------
-- Calculation of next combinational value for counter of stuffed bits:
-- 1. Erase when restarted bit stuffing.
-- 2. Upon insertion of non-fixed stuff bit increment.
-- 3. Keep previous value otherwise.
---------------------------------------------------------------------------
stuff_ctr_nxt <= 0 when (enable_prev = '0') else
stuff_ctr_add when (tran_trig_1 = '1' and
stuff_lvl_reached = '1' and
fixed_stuff = '0') else
stuff_ctr;
---------------------------------------------------------------------------
-- Counter of stuffed bits (for CRC of ISO FD).
---------------------------------------------------------------------------
stuff_ctr_proc : process(res_n, clk_sys)
begin
if (res_n = ACT_RESET) then
same_bits <= 1;
prev_bit <= RECESSIVE;
halt_reg <= '0';
enable_prev <= '0';
stuff_ctr <= 0;
fixed_prev <= '0';
elsif rising_edge(clk_sys) then
-- Registering fixed stuff value for edge detection
enable_prev <= enable;
stuff_ctr <= stuff_ctr;
if (enable = '1') then
-- Start of the bit stuffing
if (enable_prev = '0') then
prev_bit <= RECESSIVE;
same_bits <= 1;
stuff_ctr <= 0;
fixed_prev <= '0';
-- Trigger signal
elsif (tran_trig_1 = '1') then
fixed_prev <= fixed_stuff;
-- When stuffing method is changed in the beginning of
-- CRC field the stuffing counter needs to be erased!
if (fixed_stuff = '1' and fixed_prev = '0') then
prev_bit <= not prev_bit;
halt_reg <= '1';
same_bits <= 1;
-- If number of bits was reached
elsif (same_bits = unsigned(length) and fixed_stuff = '0') or
(same_bits = unsigned(length) + 1 and fixed_stuff = '1')
--Fixed stuff must be plus one since also the stuffed bit is
--counted! In normal bit stuffing when bit is stuffed same_bits
--is erased and counted from first bit after stuffed bit!
then
same_bits <= 1;
prev_bit <= not prev_bit;
halt_reg <= '1';
-- Stuff bit occured increase the stuffing counter!
-- but only in the case of the original stuffing method
if (fixed_stuff = '0') then
stuff_ctr <= (stuff_ctr + 1) mod 8;
else
stuff_ctr <= stuff_ctr;
end if;
else -- Not reached nuber of bits for stuff bit
-- If fixed stuffing selected or incoming bit is equal with
-- last bit
if (data_in = prev_bit or fixed_stuff = '1') then
same_bits <= (same_bits + 1) mod 8;
else
same_bits <= 1;
end if;
halt_reg <= '0';
prev_bit <= data_in;
end if;
if (res_n = ACT_RESET) then
stuff_ctr <= 0;
elsif rising_edge(clk_sys) then
if (enable = '1') then
stuff_ctr <= stuff_ctr_nxt;
end if;
end if;
end process;
else
prev_bit <= prev_bit;
same_bits <= same_bits;
end if;
else
---------------------------------------------------------------------------
-- Reset counter of equal consecutive bits to 1 with bit processing when:
-- 1. Processing first bit of fixed bit stuffing
-- 2. Stuff level was reached -> Stuff bit will be inserted
-- 3. Processed bit differs from previous bit (data out register) and
-- regular stuffing is used.
---------------------------------------------------------------------------
same_bits_rst_trig <= '1' when (non_fix_to_fix_chng = '1') or
(stuff_lvl_reached = '1') or
(data_in /= data_out and fixed_stuff = '0')
else
'0';
---------------------------------------------------------------------------
-- Reset counter of equal consecutive bits:
-- 1. Upon start of bit-stuffing
-- 2. When processing bit and should be restarted by dedicated signal.
---------------------------------------------------------------------------
same_bits_rst <= '1' when (enable_prev = '0') or
(tran_trig_1 = '1' and same_bits_rst_trig = '1')
else
'0';
---------------------------------------------------------------------------
-- Combinationally incremented value of equal consecutive bits of equal
-- value.
---------------------------------------------------------------------------
same_bits_add <= (same_bits + 1) mod 8;
---------------------------------------------------------------------------
-- Next value for counter of equal consecutive bits:
-- 1. Reset
-- 2. Increment if not reset when processing bit.
-- 3. Keep original value otherwise.
---------------------------------------------------------------------------
same_bits_nxt <= 1 when (same_bits_rst = '1') else
same_bits_add when (tran_trig_1 = '1') else
same_bits;
---------------------------------------------------------------------------
-- Number of stuff bits is reached when:
-- 1. Normal bit stuffing, number of same bits is equal to stuff rule
-- length. Stuff bit is already included in counting next consecutive
-- bits of equal value (recursive behaviour of bit-stuffing).
-- 2. Fixed bit stuffing, number of same bits is equal to one more than
-- rule length, since stuff bit is not included then!
---------------------------------------------------------------------------
stuff_lvl_reached <= '1' when (same_bits = unsigned(length) and fixed_stuff = '0') or
(same_bits = unsigned(length) + 1 and fixed_stuff = '1')
else
'0';
---------------------------------------------------------------------------
-- Counter of equal consecutive bits on input
---------------------------------------------------------------------------
same_bits_ctr_proc : process(res_n, clk_sys)
begin
if (res_n = ACT_RESET) then
same_bits <= 1;
halt_reg <= '0';
-- When circuit is disabled it passes the data on trigger signal
-- from input to output without Stuffing!
if (tran_trig_1 = '1') then
prev_bit <= data_in;
elsif rising_edge(clk_sys) then
if (enable = '1') then
same_bits <= same_bits_nxt;
else
prev_bit <= prev_bit;
same_bits <= 1;
end if;
end if;
end if;
end if;
end process;
data_out <= prev_bit; --Proapagating bit on output
data_halt <= halt_reg; --Propagating halt value BACK to CAN Core
---------------------------------------------------------------------------
-- Stuff bit should be inserted:
-- 1. Upon change of non-fixed to fixed bit stuffing
-- 2. Stuff counter has reached length of stuff rule.
---------------------------------------------------------------------------
insert_stuff_bit <= '1' when (non_fix_to_fix_chng = '1' or
stuff_lvl_reached = '1')
else
'0';
---------------------------------------------------------------------------
-- Calculation of output data value:
-- 1. Recessive bit after restart
-- 2. Negation of previous value when stuff bit is inserted.
-- 3. Pipe the input data upon trigger without stufffing
-- 4. Keep previous value otherwise
---------------------------------------------------------------------------
data_out_nxt_ena <= RECESSIVE when (enable_prev = '0') else
(not data_out) when (tran_trig_1 = '1' and insert_stuff_bit = '1') else
data_in when (tran_trig_1 = '1') else
data_out;
data_out_nxt <= data_out_nxt_ena when (enable = '1') else
data_in when (tran_trig_1 = '1') else
data_out;
data_out_load <= '1' when (enable = '1' or tran_trig_1 = '1') else
'0';
---------------------------------------------------------------------------
-- Output data register. Stuffed data are stored to this register in
-- trigger, or input data are piped directly to this register when
-- enable = '0'.
---------------------------------------------------------------------------
dff_data_out_reg : dff_arst
generic map(
reset_polarity => ACT_RESET,
rst_val => RECESSIVE
)
port map(
arst => res_n,
clk => clk_sys,
input => data_out_nxt,
load => data_out_load,
output => data_out
);
---------------------------------------------------------------------------
-- Halt register signals to CAN Core that it should wait for one clock
-- cycle because stuff-bit was inserted.
--
-- Next value for halt register:
-- 1. Erase upon start of bit-stuffing, or when circuit is disabled.
-- 2. Signal halt when stuff bit is inserted.
-- 3. Erase when bit is processed, but stuff bit is not inserted.
---------------------------------------------------------------------------
halt_reg_nxt <= '0' when (enable_prev = '0' or enable = '0') else
'1' when (tran_trig_1 = '1' and insert_stuff_bit = '1') else
'0' when (tran_trig_1 = '1') else
halt_reg;
---------------------------------------------------------------------------
-- Halt register instance
---------------------------------------------------------------------------
dff_halt_reg : dff_arst
generic map(
reset_polarity => ACT_RESET,
rst_val => '0'
)
port map(
arst => res_n,
clk => clk_sys,
input => halt_reg_nxt,
load => '1',
output => halt_reg
);
---------------------------------------------------------------------------
-- Propagating internal signals to output
---------------------------------------------------------------------------
bst_ctr <= stuff_ctr;
data_halt <= halt_reg; --Propagating halt value BACK to CAN Core
end architecture;
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