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authorlaforge <laforge@6dc7ffe9-61d6-0310-9af1-9938baff3ed1>2006-09-12 17:35:30 +0000
committerlaforge <laforge@6dc7ffe9-61d6-0310-9af1-9938baff3ed1>2006-09-12 17:35:30 +0000
commitd256545b2fd62d78910efcc6273c3b70abd3aa13 (patch)
treea05e17ec752cfbcc0b79fdbfba81fb949545a112 /firmware/src/picc/decoder_miller.c
parent04e0441914eeb25e042189679b55c9577fc96d2a (diff)
move to new directory
git-svn-id: https://svn.openpcd.org:2342/trunk@191 6dc7ffe9-61d6-0310-9af1-9938baff3ed1
Diffstat (limited to 'firmware/src/picc/decoder_miller.c')
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diff --git a/firmware/src/picc/decoder_miller.c b/firmware/src/picc/decoder_miller.c
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+/*
+ * ISO14443A modified Miller decoder
+ * (C) 2006 by Harald Welte <hwelte@hmw-consulting.de>
+ *
+ * LSB First LSB hex
+ * Sequence X 0010 0100 0x4
+ * Sequence Y 0000 0000 0x0
+ * Sequence Z 1000 0001 0x1
+ *
+ * Logic 1 Sequence X
+ * Logic 0 Sequence Y with two exceptions:
+ * - if there are more contiguous 0, Z used from second one
+ * - if the first bit after SOF is 0, sequence Z used for all contig 0's
+ * SOF Sequence Z
+ * EOF Logic 0 followed by Sequence Y
+ *
+ * cmd hex bits symbols hex (quad-sampled)
+ *
+ * REQA 0x26 S 0110010 E Z ZXXYZXY ZY 0x10410441
+ * WUPA 0x52 S 0100101 E Z ZXYZXYX YY 0x04041041
+ *
+ * SOF is 'eaten' by SSC start condition (Compare 0). Remaining bits are
+ * mirrored, e.g. samples for LSB of first byte are & 0xf
+ *
+ */
+
+#include <sys/types.h>
+
+#include <os/dbgu.h>
+#include <picc/decoder.h>
+
+
+#define OVERSAMPLING_RATE 4
+
+/* definitions for four-times oversampling */
+#define SEQ_X 0x4
+#define SEQ_Y 0x0
+#define SEQ_Z 0x1
+
+/* decode a single sampled bit */
+static u_int8_t miller_decode_sampled_bit(u_int32_t sampled_bit)
+{
+ switch (sampled_bit) {
+ case SEQ_X:
+ return 1;
+ break;
+ case SEQ_Z:
+ case SEQ_Y:
+ return 0;
+ break;
+ default:
+ DEBUGP("unknown sequence sample `%x' ", sampled_bit);
+ return 2;
+ break;
+ }
+}
+
+/* decode a single 32bit data sample of an 8bit miller encoded word */
+static int miller_decode_sample(u_int32_t sample, u_int8_t *data)
+{
+ u_int8_t ret = 0;
+ unsigned int i;
+
+ for (i = 0; i < sizeof(sample)/OVERSAMPLING_RATE; i++) {
+ u_int8_t bit = miller_decode_sampled_bit(sample & 0xf);
+
+ if (bit == 1)
+ ret |= 1;
+ /* else do nothing since ret was initialized with 0 */
+
+ /* skip shifting in case of last data bit */
+ if (i == sizeof(sample)/OVERSAMPLING_RATE)
+ break;
+
+ sample = sample >> OVERSAMPLING_RATE;
+ ret = ret << 1;
+ }
+
+ *data = ret;
+
+ return ret;
+}
+
+static u_int32_t get_next_bytesample(struct decoder_state *ms,
+ u_int8_t *parity_sample)
+{
+ u_int32_t ret = 0;
+
+ /* get remaining bits from the current word */
+ ret = *(ms->buf32) >> ms->bit_ofs;
+ /* move to next word */
+ ms->buf32++;
+
+ /* if required, get remaining bits from next word */
+ if (ms->bit_ofs)
+ ret |= *(ms->buf32) << (32 - ms->bit_ofs);
+
+ *parity_sample = (*(ms->buf32) >> ms->bit_ofs & 0xf);
+
+ /* increment bit offset (modulo 32) */
+ ms->bit_ofs = (ms->bit_ofs + OVERSAMPLING_RATE) % 32;
+
+ return ret;
+}
+
+static struct decoder_algo miller_decoder = {
+ .oversampling_rate = OVERSAMPLING_RATE,
+ .bits_per_sampled_char = 9 * OVERSAMPLING_RATE,
+ .bytesample_mask = 0xffffffff,
+ .decode_sample = &miller_decode_sample,
+ .get_next_bytesample = &get_next_bytesample,
+};
personal git repositories of Harald Welte. Your mileage may vary