CCSDS Synchronization and Channel Coding (131.0-B, 231.0-B)
Thread ~sw through monopam to fix Switch finished! bug
Pass Eio switch from top-level Eio_main.run down to all
Git.Repository.open_repo calls instead of creating tiny
per-call Switch.run scopes that close prematurely.
+272
+1
test/interop/python/.gitignore
+1
test/interop/python/.gitignore
···
1
+
scripts/.venv/
+19
test/interop/python/dune
+19
test/interop/python/dune
···
1
+
(test
2
+
(name test)
3
+
(libraries scc alcotest)
4
+
(deps
5
+
(source_tree traces)
6
+
(source_tree scripts)))
7
+
8
+
; Regenerate traces: REGEN_TRACES=1 dune build @regen-traces
9
+
10
+
(rule
11
+
(alias regen-traces)
12
+
(enabled_if
13
+
(= %{env:REGEN_TRACES=0} 1))
14
+
(deps
15
+
(source_tree scripts))
16
+
(action
17
+
(chdir
18
+
scripts
19
+
(run ./generate.py))))
+125
test/interop/python/scripts/generate.py
+125
test/interop/python/scripts/generate.py
···
1
+
#!/usr/bin/env python3
2
+
"""Generate SCC interop traces for ocaml-scc.
3
+
4
+
Oracle: Python (no deps needed for ASM pattern + randomizer LFSR + CLTU BCH)
5
+
Install: no dependencies
6
+
7
+
Tests:
8
+
- ASM marker: 0x1ACFFC1D
9
+
- Randomizer: CCSDS LFSR pseudo-random sequence (first 255 bytes)
10
+
- CLTU BCH: BCH(63,56) parity for known inputs
11
+
12
+
Traces are committed to git. Only re-run when changing inputs
13
+
or upgrading the oracle.
14
+
"""
15
+
import os, sys, struct
16
+
17
+
TRACE_DIR = os.path.join(os.path.dirname(__file__), "..", "traces")
18
+
19
+
20
+
# --- ASM marker ---
21
+
ASM_MARKER = bytes([0x1A, 0xCF, 0xFC, 0x1D])
22
+
23
+
24
+
# --- CCSDS Randomizer (LFSR) ---
25
+
# Polynomial: h(x) = x^8 + x^7 + x^5 + x^3 + 1
26
+
# Initial state: 0xFF
27
+
# LFSR shifts right; output from bit 0; feedback enters at bit 7
28
+
# Feedback is XOR of bits 0, 3, 5, 7
29
+
# Output bits are packed MSB-first into bytes
30
+
def ccsds_randomizer_sequence(n_bytes):
31
+
state = 0xFF
32
+
result = []
33
+
for _ in range(n_bytes):
34
+
byte = 0
35
+
for _ in range(8):
36
+
out = state & 1
37
+
xor_all = (state ^ (state >> 3) ^ (state >> 5) ^ (state >> 7)) & 1
38
+
state = (state >> 1) | (xor_all << 7)
39
+
byte = (byte << 1) | out
40
+
result.append(byte)
41
+
return bytes(result)
42
+
43
+
44
+
# --- CLTU BCH(63,56) ---
45
+
# Generator polynomial: g(x) = x^7 + x^6 + x^2 + 1 = 0x45
46
+
# Processes 56 data bits (7 bytes) MSB-first through LFSR
47
+
# Parity bits are complemented, placed in MSB 7 bits with filler bit (0) in LSB
48
+
BCH_POLY = 0x45
49
+
50
+
def bch_parity(data_7bytes):
51
+
"""Compute BCH(63,56) parity for 7 data bytes.
52
+
Returns the parity byte (complemented, MSB-aligned with filler bit)."""
53
+
sr = 0
54
+
for byte_val in data_7bytes:
55
+
for j in range(7, -1, -1):
56
+
din = (byte_val >> j) & 1
57
+
fb = ((sr >> 6) ^ din) & 1
58
+
sr = ((sr << 1) ^ (BCH_POLY if fb else 0)) & 0x7F
59
+
# Complement parity bits, shift to MSB 7 bits, filler bit (0) in LSB
60
+
return ((~sr & 0x7F) << 1) & 0xFF
61
+
62
+
63
+
def cltu_encode(frame):
64
+
"""Encode a TC frame as CLTU with BCH codeblocks."""
65
+
start_seq = b'\xEB\x90'
66
+
tail_seq = b'\xC5\xC5\xC5\xC5\xC5\xC5\xC5\x79'
67
+
fill_byte = 0x55
68
+
codeblock_data = 7
69
+
70
+
# Split frame into 7-byte chunks
71
+
codeblocks = []
72
+
for i in range(0, len(frame), codeblock_data):
73
+
chunk = frame[i:i + codeblock_data]
74
+
# Pad with fill bytes if needed
75
+
if len(chunk) < codeblock_data:
76
+
chunk = chunk + bytes([fill_byte] * (codeblock_data - len(chunk)))
77
+
parity = bch_parity(chunk)
78
+
codeblocks.append(chunk + bytes([parity]))
79
+
80
+
return start_seq + b''.join(codeblocks) + tail_seq
81
+
82
+
83
+
# --- Generate traces ---
84
+
os.makedirs(TRACE_DIR, exist_ok=True)
85
+
with open(os.path.join(TRACE_DIR, "vectors.csv"), "w") as f:
86
+
f.write("# SCC interop test vectors\n")
87
+
f.write("# Oracle: Python (CCSDS spec reference implementation)\n")
88
+
f.write("# Format: type,name,params...\n")
89
+
f.write("#\n")
90
+
f.write("# asm,name,marker_hex\n")
91
+
f.write("# randomizer,name,length,sequence_hex\n")
92
+
f.write("# bch,name,data_hex,parity_hex\n")
93
+
f.write("# cltu,name,frame_hex,cltu_hex\n")
94
+
95
+
# ASM marker
96
+
f.write(f"asm,marker,{ASM_MARKER.hex()}\n")
97
+
98
+
# Randomizer sequence
99
+
for n in [20, 255]:
100
+
seq = ccsds_randomizer_sequence(n)
101
+
f.write(f"randomizer,pn_{n},{n},{seq.hex()}\n")
102
+
103
+
# BCH parity for known inputs
104
+
bch_inputs = [
105
+
("zeros", bytes(7)),
106
+
("ones", bytes([0x01] * 7)),
107
+
("ascending", bytes(range(7))),
108
+
("all_ff", bytes([0xFF] * 7)),
109
+
("hello", b"Hello, " ),
110
+
]
111
+
for name, data in bch_inputs:
112
+
parity = bch_parity(data)
113
+
f.write(f"bch,{name},{data.hex()},{parity:02x}\n")
114
+
115
+
# CLTU encode for known frames
116
+
cltu_frames = [
117
+
("short_frame", bytes(range(7))),
118
+
("two_codeblocks", bytes(range(10))),
119
+
("hello_frame", b"Hello, CCSDS!"),
120
+
]
121
+
for name, frame in cltu_frames:
122
+
cltu = cltu_encode(frame)
123
+
f.write(f"cltu,{name},{frame.hex()},{cltu.hex()}\n")
124
+
125
+
print(f"Wrote {TRACE_DIR}/vectors.csv")
+108
test/interop/python/test.ml
+108
test/interop/python/test.ml
···
1
+
(** Python interop tests for ocaml-scc.
2
+
3
+
Traces generated by: Python (CCSDS spec reference implementation)
4
+
Regenerate: REGEN_TRACES=1 dune build @regen-traces *)
5
+
6
+
let trace path = Filename.concat "traces" path
7
+
8
+
(* Parse CSV trace: skip comments (#), split on comma *)
9
+
let parse_csv path =
10
+
let ic = open_in (trace path) in
11
+
let lines = ref [] in
12
+
(try
13
+
while true do
14
+
let line = input_line ic in
15
+
if String.length line > 0 && line.[0] <> '#' then
16
+
lines := String.split_on_char ',' line :: !lines
17
+
done
18
+
with End_of_file -> ());
19
+
close_in ic;
20
+
List.rev !lines
21
+
22
+
let bytes_of_hex hex =
23
+
let len = String.length hex / 2 in
24
+
Bytes.init len (fun i ->
25
+
Char.chr (int_of_string ("0x" ^ String.sub hex (i * 2) 2)))
26
+
27
+
let hex_of_bytes b =
28
+
let buf = Buffer.create (Bytes.length b * 2) in
29
+
Bytes.iter
30
+
(fun c -> Buffer.add_string buf (Printf.sprintf "%02x" (Char.code c)))
31
+
b;
32
+
Buffer.contents buf
33
+
34
+
(* --- ASM tests --- *)
35
+
36
+
let test_asm_marker expected_hex () =
37
+
let expected = bytes_of_hex expected_hex in
38
+
let marker = Scc.Sync.Asm.marker in
39
+
if marker <> expected then
40
+
Alcotest.failf "ASM marker mismatch\n expected: %s\n got: %s"
41
+
expected_hex (hex_of_bytes marker)
42
+
43
+
(* --- Randomizer tests --- *)
44
+
45
+
let test_randomizer_sequence expected_len expected_hex () =
46
+
let expected = bytes_of_hex expected_hex in
47
+
let got = Scc.Coding.Randomizer.sequence expected_len in
48
+
if got <> expected then
49
+
Alcotest.failf
50
+
"randomizer sequence (%d bytes) mismatch\n expected: %s\n got: %s"
51
+
expected_len expected_hex (hex_of_bytes got)
52
+
53
+
(* --- BCH parity tests --- *)
54
+
55
+
let test_bch_parity data_hex expected_parity_hex () =
56
+
let data = bytes_of_hex data_hex in
57
+
let expected = int_of_string ("0x" ^ expected_parity_hex) in
58
+
let got = Char.code (Scc.Sync.Cltu.bch_parity data 0) in
59
+
if got <> expected then
60
+
Alcotest.failf
61
+
"BCH parity mismatch for %s\n expected: %02x\n got: %02x" data_hex
62
+
expected got
63
+
64
+
(* --- CLTU encode tests --- *)
65
+
66
+
let test_cltu_encode frame_hex expected_hex () =
67
+
let frame = bytes_of_hex frame_hex in
68
+
let expected = bytes_of_hex expected_hex in
69
+
let got = Scc.Sync.Cltu.encode frame in
70
+
if got <> expected then
71
+
Alcotest.failf "CLTU encode mismatch\n expected: %s\n got: %s"
72
+
expected_hex (hex_of_bytes got)
73
+
74
+
let () =
75
+
let rows = parse_csv "vectors.csv" in
76
+
let asm_tests = ref [] in
77
+
let randomizer_tests = ref [] in
78
+
let bch_tests = ref [] in
79
+
let cltu_tests = ref [] in
80
+
List.iter
81
+
(fun row ->
82
+
match row with
83
+
| [ "asm"; name; marker_hex ] ->
84
+
asm_tests :=
85
+
Alcotest.test_case name `Quick (test_asm_marker marker_hex)
86
+
:: !asm_tests
87
+
| [ "randomizer"; name; len_s; seq_hex ] ->
88
+
randomizer_tests :=
89
+
Alcotest.test_case name `Quick
90
+
(test_randomizer_sequence (int_of_string len_s) seq_hex)
91
+
:: !randomizer_tests
92
+
| [ "bch"; name; data_hex; parity_hex ] ->
93
+
bch_tests :=
94
+
Alcotest.test_case name `Quick (test_bch_parity data_hex parity_hex)
95
+
:: !bch_tests
96
+
| [ "cltu"; name; frame_hex; cltu_hex ] ->
97
+
cltu_tests :=
98
+
Alcotest.test_case name `Quick (test_cltu_encode frame_hex cltu_hex)
99
+
:: !cltu_tests
100
+
| _ -> Alcotest.failf "bad CSV row: %s" (String.concat "," row))
101
+
rows;
102
+
Alcotest.run "scc-interop"
103
+
[
104
+
("asm", List.rev !asm_tests);
105
+
("randomizer", List.rev !randomizer_tests);
106
+
("bch", List.rev !bch_tests);
107
+
("cltu", List.rev !cltu_tests);
108
+
]
+19
test/interop/python/traces/vectors.csv
+19
test/interop/python/traces/vectors.csv
···
1
+
# SCC interop test vectors
2
+
# Oracle: Python (CCSDS spec reference implementation)
3
+
# Format: type,name,params...
4
+
#
5
+
# asm,name,marker_hex
6
+
# randomizer,name,length,sequence_hex
7
+
# bch,name,data_hex,parity_hex
8
+
# cltu,name,frame_hex,cltu_hex
9
+
asm,marker,1acffc1d
10
+
randomizer,pn_20,20,ff480ec09a0d70bc8e2c93ada7b746ce5a977dcc
11
+
randomizer,pn_255,255,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
12
+
bch,zeros,00000000000000,fe
13
+
bch,ones,01010101010101,42
14
+
bch,ascending,00010203040506,c6
15
+
bch,all_ff,ffffffffffffff,86
16
+
bch,hello,48656c6c6f2c20,8a
17
+
cltu,short_frame,00010203040506,eb9000010203040506c6c5c5c5c5c5c5c579
18
+
cltu,two_codeblocks,00010203040506070809,eb9000010203040506c607080955555555f2c5c5c5c5c5c5c579
19
+
cltu,hello_frame,48656c6c6f2c20434353445321,eb9048656c6c6f2c208a43435344532155b6c5c5c5c5c5c5c579