altos: Rename 'core' to 'kernel'

[fw/altos] / src / kernel / ao_fec_tx.c

diff --git a/src/kernel/ao_fec_tx.c b/src/kernel/ao_fec_tx.c
new file mode 100644 (file)
index 0000000..4941d74
--- /dev/null
+++ b/src/kernel/ao_fec_tx.c
@@ -0,0 +1,134 @@
+/*
+ * Copyright © 2012 Keith Packard <keithp@keithp.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
+ */
+
+#include <ao_fec.h>
+#include <stdio.h>
+
+#if AO_FEC_DEBUG
+void
+ao_fec_dump_bytes(const uint8_t *bytes, uint16_t len, const char *name)
+{
+       uint16_t        i;
+
+       printf ("%s (%d):", name, len);
+       for (i = 0; i < len; i++) {
+               if ((i & 7) == 0)
+                       printf ("\n\t%02x:", i);
+               printf(" %02x", bytes[i]);
+       }
+       printf ("\n");
+}
+#endif
+
+uint16_t
+ao_fec_crc(const uint8_t *bytes, uint8_t len)
+{
+       uint16_t        crc = AO_FEC_CRC_INIT;
+
+       while (len--)
+               crc = ao_fec_crc_byte(*bytes++, crc);
+       return crc;
+}
+
+/*
+ * len is the length of the data; the crc will be
+ * the fist two bytes after that
+ */
+
+uint8_t
+ao_fec_check_crc(const 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;
+}
+
+/*
+ * Compute CRC and trellis-terminator/interleave-pad bytes
+ */
+static uint8_t
+ao_fec_prepare(const uint8_t *in, uint8_t len, uint8_t *extra)
+{
+       uint16_t        crc = ao_fec_crc (in, len);
+       uint8_t         i = 0;
+       uint8_t         num_fec;
+
+       /* Append 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--)
+               extra[i++] = AO_FEC_TRELLIS_TERMINATOR;
+       return i;
+}
+
+const uint8_t ao_fec_whiten_table[] = {
+#include "ao_whiten.h"
+};
+
+static const uint8_t ao_fec_encode_table[16] = {
+/* next 0  1     state */
+       0, 3,   /* 000 */
+       1, 2,   /* 001 */
+       3, 0,   /* 010 */
+       2, 1,   /* 011 */
+       3, 0,   /* 100 */
+       2, 1,   /* 101 */
+       0, 3,   /* 110 */
+       1, 2    /* 111 */
+};
+
+uint8_t
+ao_fec_encode(const uint8_t *in, uint8_t len, uint8_t *out)
+{
+       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;
+                       }
+               }
+
+               interleave = 0;
+               for (bit = 0; bit < 4 * 4; bit++) {
+                       uint8_t byte_shift = (bit & 0x3) << 3;
+                       uint8_t bit_shift = (bit & 0xc) >> 1;
+
+                       interleave = (interleave << 2) | ((encode >> (byte_shift + bit_shift)) & 0x3);
+               }
+               *out++ = interleave >> 24;
+               *out++ = interleave >> 16;
+               *out++ = interleave >> 8;
+               *out++ = interleave >> 0;
+       }
+       return (len + extra_len) * 2;
+}