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-rw-r--r--src/core/ao_fec.h26
-rw-r--r--src/core/ao_fec_tx.c118
-rw-r--r--src/core/ao_viterbi.c46
3 files changed, 136 insertions, 54 deletions
diff --git a/src/core/ao_fec.h b/src/core/ao_fec.h
index d4f64b74..f3f55fa8 100644
--- a/src/core/ao_fec.h
+++ b/src/core/ao_fec.h
@@ -24,13 +24,23 @@
#define AO_FEC_TRELLIS_TERMINATOR 0x0b
#define AO_FEC_PREPARE_EXTRA 4
+extern const uint8_t ao_fec_whiten_table[];
+
void
-ao_fec_dump_bytes(uint8_t *bytes, uint8_t len, char *name);
+ao_fec_dump_bytes(uint8_t *bytes, uint16_t len, char *name);
uint16_t
ao_fec_crc(uint8_t *bytes, uint8_t len);
/*
+ * 'len' is the length of the original data; 'bytes'
+ * must be four bytes longer than that, and the first
+ * two after 'len' must be the received crc
+ */
+uint8_t
+ao_fec_check_crc(uint8_t *bytes, uint8_t len);
+
+/*
* Append CRC and terminator bytes, returns resulting length.
* 'out' must be at least len + AO_FEC_PREPARE_EXTRA bytes long
*/
@@ -46,18 +56,12 @@ void
ao_fec_whiten(uint8_t *in, uint8_t len, uint8_t *out);
/*
- * Encode data. 'out' must be len*2 bytes long
+ * Encode and interleave data. 'out' must be len*2 bytes long
*/
uint8_t
ao_fec_encode(uint8_t *in, uint8_t len, uint8_t *out);
/*
- * Interleave data. 'out' must be 'len' bytes long
- */
-uint8_t
-ao_fec_interleave(uint8_t *in, uint8_t len, uint8_t *out);
-
-/*
* Decode data. 'in' is one byte per bit, soft decision
* 'out' must be len/8 bytes long
*/
@@ -65,4 +69,10 @@ ao_fec_interleave(uint8_t *in, uint8_t len, uint8_t *out);
uint8_t
ao_fec_decode(uint8_t *in, uint16_t in_len, uint8_t *out);
+/*
+ * Interleave data packed in bytes. 'out' must be 'len' bytes long.
+ */
+uint16_t
+ao_fec_interleave_bytes(uint8_t *in, uint16_t len, uint8_t *out);
+
#endif /* _AO_FEC_H_ */
diff --git a/src/core/ao_fec_tx.c b/src/core/ao_fec_tx.c
index c5f410b8..c9c0a3d6 100644
--- a/src/core/ao_fec_tx.c
+++ b/src/core/ao_fec_tx.c
@@ -19,9 +19,9 @@
#include <stdio.h>
void
-ao_fec_dump_bytes(uint8_t *bytes, uint8_t len, char *name)
+ao_fec_dump_bytes(uint8_t *bytes, uint16_t len, char *name)
{
- uint8_t i;
+ uint16_t i;
printf ("%s (%d):", name, len);
for (i = 0; i < len; i++) {
@@ -57,41 +57,76 @@ ao_fec_crc(uint8_t *bytes, uint8_t len)
return crc;
}
+/*
+ * len is the length of the data; the crc will be
+ * the fist two bytes after that
+ */
+
uint8_t
-ao_fec_prepare(uint8_t *in, uint8_t len, uint8_t *out)
+ao_fec_check_crc(uint8_t *bytes, uint8_t len)
+{
+ uint16_t computed_crc = ao_fec_crc(bytes, len);
+ uint16_t received_crc = (bytes[len] << 8) | (bytes[len+1]);
+
+ return computed_crc == received_crc;
+}
+
+uint8_t
+ao_fec_prepare(uint8_t *in, uint8_t len, uint8_t *extra)
{
uint16_t crc = ao_fec_crc (in, len);
- uint8_t i;
+ uint8_t i = 0;
uint8_t num_fec;
- /* Copy data */
- for (i = 0; i < len; i++)
- out[i] = in[i];
-
/* Append CRC */
- out[i++] = crc >> 8;
- out[i++] = crc;
+ extra[i++] = crc >> 8;
+ extra[i++] = crc;
/* Append FEC -- 1 byte if odd, two bytes if even */
num_fec = 2 - (i & 1);
while (num_fec--)
- out[i++] = AO_FEC_TRELLIS_TERMINATOR;
+ extra[i++] = AO_FEC_TRELLIS_TERMINATOR;
return i;
}
-static const uint8_t whiten[] = {
+const uint8_t ao_fec_whiten_table[] = {
#include "ao_whiten.h"
};
+#if 0
void
ao_fec_whiten(uint8_t *in, uint8_t len, uint8_t *out)
{
- const uint8_t *w = whiten;
+ const uint8_t *w = ao_fec_whiten_table;
while (len--)
*out++ = *in++ ^ *w++;
}
+/*
+ * Unused as interleaving is now built in to ao_fec_encode
+ */
+
+static void
+ao_fec_interleave(uint8_t *d, uint8_t len)
+{
+ uint8_t i, j;
+
+ for (i = 0; i < len; i += 4) {
+ uint32_t interleaved = 0;
+
+ for (j = 0; j < 4 * 4; j++) {
+ interleaved <<= 2;
+ interleaved |= (d[i + (~j & 0x3)] >> (2 * ((j & 0xc) >> 2))) & 0x03;
+ }
+ d[i+0] = interleaved >> 24;
+ d[i+1] = interleaved >> 16;
+ d[i+2] = interleaved >> 8;
+ d[i+3] = interleaved;
+ }
+}
+#endif
+
static const uint8_t ao_fec_encode_table[16] = {
/* next 0 1 state */
0, 3, /* 000 */
@@ -107,38 +142,37 @@ static const uint8_t ao_fec_encode_table[16] = {
uint8_t
ao_fec_encode(uint8_t *in, uint8_t len, uint8_t *out)
{
- uint16_t fec = 0, output;
- uint8_t byte, bit;
-
- for (byte = 0; byte < len; byte++) {
- fec = (fec & 0x700) | in[byte];
- output = 0;
- for (bit = 0; bit < 8; bit++) {
- output = output << 2 | ao_fec_encode_table[fec >> 7];
- fec = (fec << 1) & 0x7ff;
+ uint8_t extra[AO_FEC_PREPARE_EXTRA];
+ uint8_t extra_len;
+ uint32_t encode, interleave;
+ uint8_t pair, byte, bit;
+ uint16_t fec = 0;
+ const uint8_t *whiten = ao_fec_whiten_table;
+
+ extra_len = ao_fec_prepare(in, len, extra);
+ for (pair = 0; pair < len + extra_len; pair += 2) {
+ encode = 0;
+ for (byte = 0; byte < 2; byte++) {
+ if (pair + byte == len)
+ in = extra;
+ fec |= *in++ ^ *whiten++;
+ for (bit = 0; bit < 8; bit++) {
+ encode = encode << 2 | ao_fec_encode_table[fec >> 7];
+ fec = (fec << 1) & 0x7ff;
+ }
}
- out[byte * 2] = output >> 8;
- out[byte * 2 + 1] = output;
- }
- return len * 2;
-}
-uint8_t
-ao_fec_interleave(uint8_t *in, uint8_t len, uint8_t *out)
-{
- uint8_t i, j;
-
- for (i = 0; i < len; i += 4) {
- uint32_t interleaved = 0;
+ interleave = 0;
+ for (bit = 0; bit < 4 * 4; bit++) {
+ uint8_t byte_shift = (bit & 0x3) << 3;
+ uint8_t bit_shift = (bit & 0xc) >> 1;
- for (j = 0; j < 4 * 4; j++) {
- interleaved <<= 2;
- interleaved |= (in[i + (~j & 0x3)] >> (2 * ((j & 0xc) >> 2))) & 0x03;
+ interleave = (interleave << 2) | ((encode >> (byte_shift + bit_shift)) & 0x3);
}
- out[i+0] = interleaved >> 24;
- out[i+1] = interleaved >> 16;
- out[i+2] = interleaved >> 8;
- out[i+3] = interleaved;
+ *out++ = interleave >> 24;
+ *out++ = interleave >> 16;
+ *out++ = interleave >> 8;
+ *out++ = interleave >> 0;
}
- return len;
+ return (len + extra_len) * 2;
}
diff --git a/src/core/ao_viterbi.c b/src/core/ao_viterbi.c
index 17464cd1..bb93bc83 100644
--- a/src/core/ao_viterbi.c
+++ b/src/core/ao_viterbi.c
@@ -18,6 +18,35 @@
#include <ao_fec.h>
#include <stdio.h>
+/*
+ * byte order repeats through 3 2 1 0
+ *
+ * bit-pair order repeats through
+ *
+ * 1/0 3/2 5/4 7/6
+ *
+ * So, the over all order is:
+ *
+ * 3,1/0 2,1/0 1,1/0 0,1/0
+ * 3,3/2 2,3/2 1,3/2 0,3/2
+ * 3,5/4 2,5/4 1,5/4 0,5/4
+ * 3,7/6 2,7/6 1,7/6 0,7/6
+ *
+ * The raw bit order is thus
+ *
+ * 1e/1f 16/17 0e/0f 06/07
+ * 1c/1d 14/15 0c/0d 04/05
+ * 1a/1b 12/13 0a/0b 02/03
+ * 18/19 10/11 08/09 00/01
+ */
+
+static inline uint16_t ao_interleave_index(uint16_t i) {
+ uint8_t l = i & 0x1e;
+ uint16_t h = i & ~0x1e;
+ uint8_t o = 0x1e ^ (((l >> 2) & 0x6) | ((l << 2) & 0x18));
+ return h | o;
+}
+
struct ao_soft_sym {
uint8_t a, b;
};
@@ -70,6 +99,9 @@ ao_fec_decode(uint8_t *in, uint16_t len, uint8_t *out)
uint8_t n; /* next cost/bits index */
uint8_t state; /* state index */
uint8_t bit; /* original encoded bit index */
+ const uint8_t *whiten = ao_fec_whiten_table;
+ uint16_t interleave; /* input byte array index */
+ struct ao_soft_sym s; /* input symbol pair */
p = 0;
for (state = 0; state < NUM_STATE; state++) {
@@ -82,7 +114,13 @@ ao_fec_decode(uint8_t *in, uint16_t len, uint8_t *out)
for (i = 0; i < len; i += 2) {
b = i/2;
n = p ^ 1;
- struct ao_soft_sym s = { .a = in[i], .b = in[i+1] };
+
+ /* Fetch one pair of input bytes, de-interleaving
+ * the input.
+ */
+ interleave = ao_interleave_index(i);
+ s.a = in[interleave];
+ s.b = in[interleave+1];
/* Reset next costs to 'impossibly high' values so that
* the first path through this state is cheaper than this
@@ -159,10 +197,10 @@ ao_fec_decode(uint8_t *in, uint16_t len, uint8_t *out)
}
#if 0
- printf ("\tbit %3d min_cost %5d old bit %3d old_state %x bits %02x\n",
- i/2, min_cost, o + 8, min_state, (bits[p][min_state] >> dist) & 0xff);
+ printf ("\tbit %3d min_cost %5d old bit %3d old_state %x bits %02x whiten %0x\n",
+ i/2, min_cost, o + 8, min_state, (bits[p][min_state] >> dist) & 0xff, *whiten);
#endif
- out[o >> 3] = bits[p][min_state] >> dist;
+ *out++ = (bits[p][min_state] >> dist) ^ *whiten++;
o += 8;
}
}
generated by cgit v1.2.3 (git 2.39.1) at 2025-10-22 19:19:09 +0000