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Harden RSSI RX FSM filtering and payload timing #1456

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2c34532
fix(rssi): harden RX FSM filtering and payload timing
bengineerd Jul 7, 2026
e0a05a9
Merge remote-tracking branch 'origin/rssi-regression-foundation' into…
bengineerd Jul 7, 2026
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177 changes: 110 additions & 67 deletions protocols/rssi/v1/rtl/RssiRxFsm.vhd
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Original file line number Diff line number Diff line change
Expand Up @@ -57,7 +57,7 @@ entity RssiRxFsm is
WINDOW_ADDR_SIZE_G : positive := 7; -- 2^WINDOW_ADDR_SIZE_G = Number of segments
HEADER_CHKSUM_EN_G : boolean := true;
SEGMENT_ADDR_SIZE_G : positive := 3 -- 2^SEGMENT_ADDR_SIZE_G = Number of 64 bit wide data words
);
);
port (
clk_i : in sl;
rst_i : in sl;
Expand Down Expand Up @@ -121,35 +121,35 @@ entity RssiRxFsm is
-- SSI Application side interface OUT
appSsiMaster_o : out SsiMasterType;
appSsiSlave_i : in SsiSlaveType

);
end entity RssiRxFsm;

architecture rtl of RssiRxFsm is

-- Init SSI bus
constant SSI_MASTER_INIT_C : SsiMasterType := axis2SsiMaster(RSSI_AXIS_CONFIG_C, AXI_STREAM_MASTER_INIT_C);
constant SSI_SLAVE_NOTRDY_C : SsiSlaveType := axis2SsiSlave(RSSI_AXIS_CONFIG_C, AXI_STREAM_SLAVE_INIT_C, AXI_STREAM_CTRL_UNUSED_C);
constant SSI_SLAVE_RDY_C : SsiSlaveType := axis2SsiSlave(RSSI_AXIS_CONFIG_C, AXI_STREAM_SLAVE_FORCE_C, AXI_STREAM_CTRL_UNUSED_C);

type tspStateType is (
type TspStateType is (
--
WAIT_SOF_S,
CHECK_S,
SYN_CHECK_S,
VALID_S,
DROP_S,
DATA_S
);
);

type AppStateType is (
--
CHECK_BUFFER_S,
READ_S,
DATA_S,
SENT_S
);
);

type RegType is record

-- Reception buffer window
windowArray : WindowTypeArray(0 to 2 ** WINDOW_ADDR_SIZE_G-1);

Expand All @@ -163,16 +163,20 @@ architecture rtl of RssiRxFsm is
rxBufferAddr : slv(WINDOW_ADDR_SIZE_G-1 downto 0);
--
segmentWe : sl;
segmentData : slv(RSSI_WORD_WIDTH_C*8-1 downto 0);

-- Packet flags
rxF : flagsType;

-- Received RSSI parameters
rxParam : RssiParamType;
rxParam : RssiParamType;
synParam : RssiParamType;

rxHeadLen : slv(7 downto 0);
rxSeqN : slv(7 downto 0); -- Received seqN
rxAckN : slv(7 downto 0); -- Received ackN
synEof : sl;
synEofe : sl;

--
chkEn : sl;
Expand Down Expand Up @@ -205,7 +209,6 @@ architecture rtl of RssiRxFsm is
-- State Machine
appState : AppStateType;
rxAppState : slv(3 downto 0);

end record RegType;

constant REG_INIT_C : RegType := (
Expand All @@ -221,17 +224,21 @@ architecture rtl of RssiRxFsm is
rxBufferAddr => (others => '0'),

--
segmentWe => '0',
segmentWe => '0',
segmentData => (others => '0'),

-- Packet flags
rxF => (others => ('0')),

-- Received RSSI parameters
rxParam => RSSI_PARAM_INIT_C,
rxParam => RSSI_PARAM_INIT_C,
synParam => RSSI_PARAM_INIT_C,

rxHeadLen => (others => '0'), -- Received seqN
rxSeqN => (others => '0'), -- Received seqN
rxAckN => (others => '0'), -- Received ackN
synEof => '0',
synEofe => '0',

--
chkEn => '0',
Expand Down Expand Up @@ -307,6 +314,9 @@ begin
v.rxHeaderAddr := (others => '0');
v.rxSegmentAddr := (others => '1'); -- "-1" so the first address after increment to be 0
v.segmentWe := '0';
v.synParam := RSSI_PARAM_INIT_C;
v.synEof := '0';
v.synEofe := '0';

-- Ready until SOF received
-- Also flush any dropped or non SOF segments
Expand Down Expand Up @@ -371,17 +381,17 @@ begin
if (v.rxF.syn = '1') then

-- Register SYN header word 0 parameters
v.chkLen := 3; -- TODO make generic
v.rxParam.version := r.headerData (31 downto 28);
v.rxParam.chksumEn := r.headerData (26 downto 26);
v.rxParam.maxOutsSeg := r.headerData (23 downto 16);
v.rxParam.maxSegSize := r.headerData (15 downto 0);
v.chkLen := 3; -- TODO make generic
v.synParam.version := r.headerData (31 downto 28);
v.synParam.chksumEn := r.headerData (26 downto 26);
v.synParam.maxOutsSeg := r.headerData (23 downto 16);
v.synParam.maxSegSize := r.headerData (15 downto 0);

--
if (v.rxF.ack = '1' and v.rxAckN /= lastAckN_i) then
-- Acknowledgment not valid
v.tspState := DROP_S;
elsif (v.rxF.eack = '1' or v.rxF.rst = '1' or v.rxF.busy = '1') then
elsif (v.rxF.eack = '1' or v.rxF.rst = '1' or v.rxF.nul = '1' or v.rxF.busy = '1') then
-- Wrong flags
v.tspState := DROP_S;
else
Expand All @@ -390,12 +400,14 @@ begin
end if;

-- Segment is ACK, DATA, RST, or NULL
elsif (v.rxF.syn = '0' and v.rxF.eack = '0' and chksumValid_i = '1') then --
elsif (v.rxF.syn = '0' and chksumValid_i = '1') then --

-- Check header
if (
-- Checksum
s_chksumOk = '1' and
-- EACK is not supported by this RSSI profile
v.rxF.eack = '0' and
-- Check length
r.rxHeadLen = toSlv(8, 8) and
-- Check SeqN range
Expand All @@ -404,14 +416,24 @@ begin
(r.rxAckN - lastAckN_i) <= txWindowSize_i
) then
-- Valid data segment
if (r.rxF.data = '1' and v.rxF.nul = '0' and v.rxF.rst = '0') then
-- Wait if the buffer full
-- Note: Deadlock possibility! If the peer is not accepting data!
if (r.windowArray(conv_integer(r.rxBufferAddr)).occupied = '0') then
-- Go to data segment
v.tspState := DATA_S;
if (r.rxF.data = '1' and
v.rxF.ack = '1' and
v.rxF.nul = '0' and
v.rxF.rst = '0' and
v.rxF.busy = '0') then
-- Only the next in-order DATA segment may enter the payload buffer.
if (r.rxSeqN - r.inOrderSeqN = 1) then
-- Wait if the buffer full
-- Note: Deadlock possibility! If the peer is not accepting data!
if (r.windowArray(conv_integer(r.rxBufferAddr)).occupied = '0') then
-- Go to data segment
v.tspState := DATA_S;
else
-- Buffer is full -> drop segment
v.tspState := DROP_S;
end if;
else
-- Buffer is full -> drop segment
-- Duplicate DATA -> drop without touching the payload buffer
v.tspState := DROP_S;
end if;
elsif (r.rxF.data = '0') then
Expand Down Expand Up @@ -456,11 +478,11 @@ begin
-- Register SYN header word 1 parameters
if (r.rxHeaderAddr = x"01" and r.tspSsiMaster.valid = '1') then
-- Syn parameters
v.rxParam.retransTout := r.headerData (63 downto 48);
v.rxParam.cumulAckTout := r.headerData (47 downto 32);
v.rxParam.nullSegTout := r.headerData (31 downto 16);
v.rxParam.maxRetrans := r.headerData (15 downto 8);
v.rxParam.maxCumAck := r.headerData (7 downto 0);
v.synParam.retransTout := r.headerData (63 downto 48);
v.synParam.cumulAckTout := r.headerData (47 downto 32);
v.synParam.nullSegTout := r.headerData (31 downto 16);
v.synParam.maxRetrans := r.headerData (15 downto 8);
v.synParam.maxCumAck := r.headerData (7 downto 0);
--
end if;

Expand All @@ -473,9 +495,11 @@ begin
if (r.tspSsiMaster.valid = '1') then

-- Syn parameters
v.rxParam.maxOutofseq := r.headerData (63 downto 56);
v.rxParam.timeoutUnit := r.headerData (55 downto 48);
v.rxParam.connectionId(31 downto 0) := r.headerData (47 downto 16);
v.synParam.maxOutofseq := r.headerData (63 downto 56);
v.synParam.timeoutUnit := r.headerData (55 downto 48);
v.synParam.connectionId(31 downto 0) := r.headerData (47 downto 16);
v.synEof := r.tspSsiMaster.eof;
v.synEofe := r.tspSsiMaster.eofe;

-- Tsp parameters
v.tspSsiSlave := SSI_SLAVE_NOTRDY_C;
Expand All @@ -489,9 +513,13 @@ begin
-- Checksum
s_chksumOk = '1' and
-- Check length
r.rxHeadLen = toSlv(24, 8)
r.rxHeadLen = toSlv(24, 8) and
-- Check frame boundary
r.synEof = '1' and
r.synEofe = '0'
) then
-- Header is valid
v.rxParam := r.synParam;
v.tspState := VALID_S;
else
-- Header not valid
Expand Down Expand Up @@ -534,7 +562,7 @@ begin
v.windowArray(conv_integer(r.rxBufferAddr)).keep := tspSsiMaster_i.keep(RSSI_WORD_WIDTH_C-1 downto 0);

-- Save packet length (+1 because it has not incremented for EOF yet)
v.windowArray(conv_integer(r.rxBufferAddr)).segSize := conv_integer(r.rxSegmentAddr(SEGMENT_ADDR_SIZE_G-1 downto 0))+1;
v.windowArray(conv_integer(r.rxBufferAddr)).segSize := conv_integer(v.rxSegmentAddr(SEGMENT_ADDR_SIZE_G-1 downto 0));

-- Check EOF Error
if (tspSsiMaster_i.eofe = '0') then
Expand Down Expand Up @@ -658,41 +686,14 @@ begin
) then
--
v.txBufferAddr := r.txBufferAddr;

if (appSsiSlave_i.pause = '0') then

v.appSsiMaster.sof := '1';
v.appSsiMaster.valid := '1';
v.appSsiMaster.strb := (others => '1');
v.appSsiMaster.dest := (others => '0');
v.appSsiMaster.keep(RSSI_WORD_WIDTH_C-1 downto 0) := r.windowArray(conv_integer(r.txBufferAddr)).keep;
v.appSsiMaster.eof := '1';
v.appSsiMaster.eofe := '0';
v.appSsiMaster.data(RSSI_WORD_WIDTH_C*8-1 downto 0) := rdBuffData_i;
v.txSegmentAddr := r.txSegmentAddr;

v.appState := SENT_S;
end if;
v.appState := READ_S;
-- Data segment in buffer longer than one word go to DATA_S
elsif (r.windowArray(conv_integer(r.txBufferAddr)).occupied = '1' and
r.windowArray(conv_integer(r.txBufferAddr)).segType = "001" -- Data segment type
) then
--
v.txBufferAddr := r.txBufferAddr;

if (appSsiSlave_i.pause = '0') then

v.appSsiMaster.sof := '1';
v.appSsiMaster.valid := '1';
v.appSsiMaster.strb := (others => '1');
v.appSsiMaster.dest := (others => '0');
v.appSsiMaster.eof := '0';
v.appSsiMaster.eofe := '0';
v.appSsiMaster.data(RSSI_WORD_WIDTH_C*8-1 downto 0) := rdBuffData_i;
v.txSegmentAddr := r.txSegmentAddr + 1;

v.appState := DATA_S;
end if;
v.appState := READ_S;
-- None data segment type (Go directly to SENT_S)
elsif (r.windowArray(conv_integer(r.txBufferAddr)).occupied = '1') then
--
Expand All @@ -706,24 +707,56 @@ begin
v.appState := CHECK_BUFFER_S;
end if;
----------------------------------------------------------------------
when DATA_S =>
when READ_S =>
v.rxAppState := x"1";

-- Counters
v.txBufferAddr := r.txBufferAddr;
v.rxLastSeqN := r.rxLastSeqN;

if (appSsiSlave_i.pause = '0') then
v.appSsiMaster.sof := '1';
v.appSsiMaster.valid := '1';
v.appSsiMaster.strb := (others => '1');
v.appSsiMaster.dest := (others => '0');
v.appSsiMaster.eofe := '0';
v.appSsiMaster.data(RSSI_WORD_WIDTH_C*8-1 downto 0) := rdBuffData_i;

if (r.windowArray(conv_integer(r.txBufferAddr)).segSize = 0) then
v.appSsiMaster.keep(RSSI_WORD_WIDTH_C-1 downto 0) := r.windowArray(conv_integer(r.txBufferAddr)).keep;
v.appSsiMaster.eof := '1';
v.txSegmentAddr := r.txSegmentAddr;
v.appState := SENT_S;
else
v.appSsiMaster.keep(RSSI_WORD_WIDTH_C-1 downto 0) := (others => '1');
v.appSsiMaster.eof := '0';
v.txSegmentAddr := r.txSegmentAddr + 1;
v.appState := DATA_S;
end if;
else
v.appSsiMaster.valid := '0';
v.txSegmentAddr := r.txSegmentAddr;
end if;
----------------------------------------------------------------------
when DATA_S =>
v.rxAppState := x"2";

-- Counters
v.txBufferAddr := r.txBufferAddr;
v.rxLastSeqN := r.rxLastSeqN;

-- SSI parameters
v.appSsiMaster.sof := '0';
v.appSsiMaster.strb := (others => '1');
v.appSsiMaster.keep(RSSI_WORD_WIDTH_C-1 downto 0) := (others => '1');
v.appSsiMaster.dest := (others => '0');
v.appSsiMaster.eof := '0';
v.appSsiMaster.eofe := '0';
v.appSsiMaster.data(RSSI_WORD_WIDTH_C*8-1 downto 0) := rdBuffData_i;

-- Next state condition
-- When segment address reaches segment size then go to SENT_S
if (r.txSegmentAddr >= r.windowArray(conv_integer(r.txBufferAddr)).segSize) then
if (r.txSegmentAddr >= r.windowArray(conv_integer(r.txBufferAddr)).segSize and appSsiSlave_i.pause = '0') then

-- Send EOF at the end of the segment
v.appSsiMaster.valid := '1';
Expand All @@ -748,7 +781,7 @@ begin
end if;
----------------------------------------------------------------------
when SENT_S =>
v.rxAppState := x"2";
v.rxAppState := x"3";

-- Register the sent SeqN (this means that the place has been freed and the SeqN can be Acked)
v.rxLastSeqN := r.windowArray(conv_integer(r.txBufferAddr)).seqN;
Expand Down Expand Up @@ -781,6 +814,10 @@ begin
----------------------------------------------------------------------
end case;

if (v.segmentWe = '1') then
v.segmentData := tspSsiMaster_i.data(RSSI_WORD_WIDTH_C*8-1 downto 0);
end if;

-- Combinatorial outputs before the reset
rdBuffAddr_o <= v.txBufferAddr & v.txSegmentAddr(SEGMENT_ADDR_SIZE_G-1 downto 0);
-- Transport side SSI output
Expand All @@ -797,7 +834,11 @@ begin
-- Write and read ports
wrBuffAddr_o <= r.rxBufferAddr & r.rxSegmentAddr(SEGMENT_ADDR_SIZE_G-1 downto 0);
wrBuffWe_o <= r.segmentWe;
wrBuffData_o <= r.tspSsiMaster.data(RSSI_WORD_WIDTH_C*8-1 downto 0);
if r.segmentWe = '1' then
wrBuffData_o <= r.segmentData;
else
wrBuffData_o <= r.tspSsiMaster.data(RSSI_WORD_WIDTH_C*8-1 downto 0);
end if;

-- Assign outputs
rxFlags_o <= r.rxF;
Expand All @@ -824,5 +865,7 @@ begin
r <= rin after TPD_G;
end if;
end process seq;

---------------------------------------------------------------------

end architecture rtl;
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