|
|
--
|
|
|
-- SpaceWire Exchange Level Controller.
|
|
|
--
|
|
|
-- This entity implements exchange level aspects of the SpaceWire protocol.
|
|
|
-- It handles connection setup, error detection and flow control.
|
|
|
--
|
|
|
|
|
|
library ieee;
|
|
|
use ieee.std_logic_1164.all;
|
|
|
use ieee.numeric_std.all;
|
|
|
use work.spwpkg.all;
|
|
|
|
|
|
entity spwlink is
|
|
|
|
|
|
generic (
|
|
|
-- Reset time expressed in system clock cycles.
|
|
|
-- Should be 6.4 us (5.82 us .. 7.2 us) according to the standard.
|
|
|
reset_time: integer
|
|
|
);
|
|
|
|
|
|
port (
|
|
|
-- System clock.
|
|
|
clk: in std_logic;
|
|
|
|
|
|
-- Synchronous reset (active-high).
|
|
|
-- Disconnects, resets error conditions, puts the link state machine
|
|
|
-- in state ErrorReset.
|
|
|
rst: in std_logic;
|
|
|
|
|
|
-- Link level inputs.
|
|
|
linki: in spw_link_in_type;
|
|
|
|
|
|
-- Link level outputs.
|
|
|
linko: out spw_link_out_type;
|
|
|
|
|
|
-- Receiver enable signal to spwrecv.
|
|
|
rxen: out std_logic;
|
|
|
|
|
|
-- Output signals from spwrecv.
|
|
|
recvo: in spw_recv_out_type;
|
|
|
|
|
|
-- Input signals for spwxmit.
|
|
|
xmiti: out spw_xmit_in_type;
|
|
|
|
|
|
-- Output signals from spwxmit.
|
|
|
xmito: in spw_xmit_out_type
|
|
|
);
|
|
|
|
|
|
end entity spwlink;
|
|
|
|
|
|
architecture spwlink_arch of spwlink is
|
|
|
|
|
|
-- Convert boolean to std_logic.
|
|
|
type bool_to_logic_type is array(boolean) of std_ulogic;
|
|
|
constant bool_to_logic: bool_to_logic_type := (false => '0', true => '1');
|
|
|
|
|
|
-- State machine.
|
|
|
type state_type is (
|
|
|
S_ErrorReset, S_ErrorWait, S_Ready, S_Started, S_Connecting, S_Run );
|
|
|
|
|
|
-- Registers
|
|
|
type regs_type is record
|
|
|
-- state machine
|
|
|
state: state_type;
|
|
|
-- credit accounting
|
|
|
tx_credit: unsigned(5 downto 0);
|
|
|
rx_credit: unsigned(5 downto 0);
|
|
|
errcred: std_ulogic;
|
|
|
-- reset timer
|
|
|
timercnt: unsigned(10 downto 0);
|
|
|
timerdone: std_ulogic;
|
|
|
-- signal to transmitter
|
|
|
xmit_fct_in: std_ulogic;
|
|
|
end record;
|
|
|
|
|
|
-- Initial state
|
|
|
constant regs_reset: regs_type := (
|
|
|
state => S_ErrorReset,
|
|
|
tx_credit => "000000",
|
|
|
rx_credit => "000000",
|
|
|
errcred => '0',
|
|
|
timercnt => to_unsigned(reset_time, 11),
|
|
|
timerdone => '0',
|
|
|
xmit_fct_in => '0' );
|
|
|
|
|
|
signal r: regs_type := regs_reset;
|
|
|
signal rin: regs_type;
|
|
|
|
|
|
begin
|
|
|
|
|
|
-- Combinatorial process
|
|
|
process (r, rst, linki, recvo, xmito) is
|
|
|
variable v: regs_type;
|
|
|
variable v_timerrst: std_logic;
|
|
|
begin
|
|
|
v := r;
|
|
|
v_timerrst := '0';
|
|
|
|
|
|
-- State machine.
|
|
|
case r.state is
|
|
|
|
|
|
when S_ErrorReset =>
|
|
|
-- Wait for timer.
|
|
|
if r.timercnt = 0 then
|
|
|
v.state := S_ErrorWait;
|
|
|
v_timerrst := '1';
|
|
|
end if;
|
|
|
v.errcred := '0';
|
|
|
v.xmit_fct_in := '0';
|
|
|
|
|
|
when S_ErrorWait =>
|
|
|
-- Wait for 2 timer periods.
|
|
|
if ((recvo.errdisc or recvo.errpar or recvo.erresc) = '1') or
|
|
|
((recvo.gotfct or recvo.tick_out or recvo.rxchar) = '1') then
|
|
|
-- Note: spwrecv will never issue errpar, erresc, gotfct,
|
|
|
-- tick_out or rxchar before the first NULL has been seen.
|
|
|
-- Therefore it's ok here to bail on those conditions
|
|
|
-- without explicitly testing got_null.
|
|
|
v.state := S_ErrorReset; -- error, go back to reset
|
|
|
v_timerrst := '1';
|
|
|
elsif r.timercnt = 0 then
|
|
|
if r.timerdone = '1' then
|
|
|
v.state := S_Ready;
|
|
|
v_timerrst := '1';
|
|
|
end if;
|
|
|
end if;
|
|
|
|
|
|
when S_Ready =>
|
|
|
-- Wait for link start.
|
|
|
if ((recvo.errdisc or recvo.errpar or recvo.erresc) = '1') or
|
|
|
((recvo.gotfct or recvo.tick_out or recvo.rxchar) = '1') then
|
|
|
v.state := S_ErrorReset; -- error, go back to reset
|
|
|
v_timerrst := '1';
|
|
|
elsif (linki.linkdis = '0') and (r.xmit_fct_in = '1') and
|
|
|
((linki.linkstart or (linki.autostart and recvo.gotnull)) = '1') then
|
|
|
v.state := S_Started; -- link enabled; start sending NULL
|
|
|
v_timerrst := '1';
|
|
|
end if;
|
|
|
|
|
|
when S_Started =>
|
|
|
-- Wait for NULL.
|
|
|
if ((recvo.errdisc or recvo.errpar or recvo.erresc) = '1') or
|
|
|
((recvo.gotfct or recvo.tick_out or recvo.rxchar) = '1') or
|
|
|
((r.timercnt = 0) and r.timerdone = '1') then
|
|
|
v.state := S_ErrorReset; -- error, go back to reset
|
|
|
v_timerrst := '1';
|
|
|
elsif recvo.gotnull = '1' then
|
|
|
v.state := S_Connecting; -- received null, continue
|
|
|
v_timerrst := '1';
|
|
|
end if;
|
|
|
|
|
|
when S_Connecting =>
|
|
|
-- Wait for FCT.
|
|
|
if ((recvo.errdisc or recvo.errpar or recvo.erresc) = '1') or
|
|
|
((recvo.tick_out or recvo.rxchar) = '1') or
|
|
|
((r.timercnt = 0) and r.timerdone = '1') then
|
|
|
v.state := S_ErrorReset; -- error, go back to reset
|
|
|
v_timerrst := '1';
|
|
|
elsif recvo.gotfct = '1' then
|
|
|
v.state := S_Run; -- got FCT, init completed
|
|
|
end if;
|
|
|
|
|
|
when S_Run =>
|
|
|
-- All is well.
|
|
|
if ((recvo.errdisc or recvo.errpar or recvo.erresc) = '1') or
|
|
|
(r.errcred = '1') or
|
|
|
(linki.linkdis = '1') then
|
|
|
v.state := S_ErrorReset; -- error, go back to reset
|
|
|
v_timerrst := '1';
|
|
|
end if;
|
|
|
|
|
|
when others =>
|
|
|
v.state := S_ErrorReset; -- recover from invalid state
|
|
|
v_timerrst := '1';
|
|
|
|
|
|
end case;
|
|
|
|
|
|
-- Update credit counters.
|
|
|
if r.state = S_ErrorReset then
|
|
|
|
|
|
-- reset credit
|
|
|
v.tx_credit := to_unsigned(0, v.tx_credit'length);
|
|
|
v.rx_credit := to_unsigned(0, v.rx_credit'length);
|
|
|
|
|
|
else
|
|
|
|
|
|
-- update TX credit
|
|
|
if recvo.gotfct = '1' then
|
|
|
-- just received a FCT token
|
|
|
v.tx_credit := v.tx_credit + to_unsigned(8, v.tx_credit'length);
|
|
|
if r.tx_credit > 48 then
|
|
|
-- received too many FCT tokens
|
|
|
v.errcred := '1';
|
|
|
end if;
|
|
|
end if;
|
|
|
if xmito.txack = '1' then
|
|
|
-- just sent one byte
|
|
|
v.tx_credit := v.tx_credit - to_unsigned(1, v.tx_credit'length);
|
|
|
end if;
|
|
|
|
|
|
-- update RX credit after sending FCT
|
|
|
if xmito.fctack = '1' then
|
|
|
-- just sent a FCT token
|
|
|
v.rx_credit := v.rx_credit + to_unsigned(8, v.rx_credit'length);
|
|
|
end if;
|
|
|
|
|
|
-- decide about sending FCT tokens
|
|
|
v.xmit_fct_in := bool_to_logic( (v.rx_credit <= 48) and
|
|
|
(v.rx_credit + to_unsigned(8, v.rx_credit'length) <= unsigned(linki.rxroom)) );
|
|
|
|
|
|
-- update RX credit after receiving character
|
|
|
if recvo.rxchar = '1' then
|
|
|
-- just received a character
|
|
|
v.rx_credit := v.rx_credit - to_unsigned(1, v.rx_credit'length);
|
|
|
if r.rx_credit = 0 then
|
|
|
-- remote transmitter violated its credit
|
|
|
v.errcred := '1';
|
|
|
end if;
|
|
|
end if;
|
|
|
|
|
|
end if;
|
|
|
|
|
|
-- Update the initializaton reset timer.
|
|
|
if v_timerrst = '1' then
|
|
|
v.timercnt := to_unsigned(reset_time, v.timercnt'length);
|
|
|
v.timerdone := '0';
|
|
|
else
|
|
|
if r.timercnt = 0 then
|
|
|
v.timercnt := to_unsigned(reset_time, v.timercnt'length);
|
|
|
v.timerdone := '1';
|
|
|
else
|
|
|
v.timercnt := r.timercnt - 1;
|
|
|
end if;
|
|
|
end if;
|
|
|
|
|
|
-- Reset
|
|
|
if rst = '1' then
|
|
|
v := regs_reset;
|
|
|
end if;
|
|
|
|
|
|
-- Drive link level outputs.
|
|
|
linko.started <= bool_to_logic(r.state = S_Started);
|
|
|
linko.connecting <= bool_to_logic(r.state = S_Connecting);
|
|
|
linko.running <= bool_to_logic(r.state = S_Run);
|
|
|
linko.errdisc <= recvo.errdisc and bool_to_logic(r.state = S_Run);
|
|
|
linko.errpar <= recvo.errpar and bool_to_logic(r.state = S_Run);
|
|
|
linko.erresc <= recvo.erresc and bool_to_logic(r.state = S_Run);
|
|
|
linko.errcred <= r.errcred;
|
|
|
linko.txack <= xmito.txack;
|
|
|
linko.tick_out <= recvo.tick_out and bool_to_logic(r.state = S_Run);
|
|
|
linko.ctrl_out <= recvo.ctrl_out;
|
|
|
linko.time_out <= recvo.time_out;
|
|
|
linko.rxchar <= recvo.rxchar and bool_to_logic(r.state = S_Run);
|
|
|
linko.rxflag <= recvo.rxflag;
|
|
|
linko.rxdata <= recvo.rxdata;
|
|
|
|
|
|
-- Drive receiver inputs.
|
|
|
rxen <= bool_to_logic(r.state /= S_ErrorReset);
|
|
|
|
|
|
-- Drive transmitter input signals.
|
|
|
xmiti.txen <= bool_to_logic(r.state = S_Started or
|
|
|
r.state = S_Connecting or
|
|
|
r.state = S_Run);
|
|
|
xmiti.stnull <= bool_to_logic(r.state = S_Started);
|
|
|
xmiti.stfct <= bool_to_logic(r.state = S_Connecting);
|
|
|
xmiti.fct_in <= r.xmit_fct_in;
|
|
|
xmiti.tick_in <= linki.tick_in and bool_to_logic(r.state = S_Run);
|
|
|
xmiti.ctrl_in <= linki.ctrl_in;
|
|
|
xmiti.time_in <= linki.time_in;
|
|
|
xmiti.txwrite <= linki.txwrite and bool_to_logic(r.tx_credit /= 0);
|
|
|
xmiti.txflag <= linki.txflag;
|
|
|
xmiti.txdata <= linki.txdata;
|
|
|
|
|
|
-- Update registers.
|
|
|
rin <= v;
|
|
|
end process;
|
|
|
|
|
|
-- Update registers.
|
|
|
process (clk) is
|
|
|
begin
|
|
|
if rising_edge(clk) then
|
|
|
r <= rin;
|
|
|
end if;
|
|
|
end process;
|
|
|
|
|
|
end architecture spwlink_arch;
|
|
|
|
