1 files changed, 91 insertions, 0 deletions
diff --git a/firmware/src/picc/decoder_nrzl.c b/firmware/src/picc/decoder_nrzl.c
new file mode 100644
index 0000000..a1b79aa
--- /dev/null
+++ b/firmware/src/picc/decoder_nrzl.c
@@ -0,0 +1,91 @@
+/* ISO 14443 B Rx (PCD->PICC) implementation
+ * (C) 2006 by Harald Welte <hwelte@hmw-consulting.de>
+ *
+ * speed(kbps)	106	212	424	848
+ * etu		128/fc	64/fc	32/fc	16/fc
+ * etu(usec)	9.4	4.7	2.35	1.18
+ *
+ * NRZ-L coding with logic level
+ *
+ * logic 1:	carrier high field amplitude (no modulation)
+ * logic 0:	carrier low field amplitude
+ *
+ * Character transmission format:
+ *	start bit:	logic 0
+ *	data:		eight bits, lsb first
+ *	stop bit	logic 1
+ *
+ * Frame Format:
+ *
+ * 		SOF char [EGT char, ...] EOF
+ *
+ * 	SOF: falling edge, 10..11 etu '0', rising edge in 1etu, 2..3etu '1'
+ *	EGT: between 0 and 57uS 
+ *	EOF: falling edge, 10..11 etu '0', rising edge in 1etu
+ *
+ *
+ * Sampling
+ * - sample once per bit clock, exactly in the middle of it
+ * - synchronize CARRIER_DIV TC0 to first falling edge
+ * - Configure CARRIER_DIV RA compare (rising edge) to be at
+ *   etu/2 carrier clocks.
+ * - problem: SOF 12..14etu length, therefore we cannot specify
+ *            SOF as full start condition and then sample with 10bit
+ *            frames :(
+ * 
+ */
+
+#include <errno.h>
+#include <sys/types.h>
+#include <os/dbgu.h>
+#include <picc/decoder.h>
+
+/* currently this code will only work with oversampling_rate == 1 */
+#define OVERSAMPLING_RATE 1
+
+static u_int32_t get_next_bytesample(struct decoder_state *st,
+				     u_int8_t *parity_sample)
+{
+	u_int32_t ret = 0;
+	u_int8_t bits_per_sampled_char = st->algo->bits_per_sampled_char;
+	u_int8_t bytesample_mask = st->algo->bytesample_mask;
+
+	/* FIXME: shift start and stop bit into parity_sample and just
+	 * return plain 8-bit data word */
+	
+	/* first part of 10-databit bytesample */
+	ret = (*(st->buf32) >> st->bit_ofs) & bytesample_mask;
+
+	if (st->bit_ofs > 32 - bits_per_sampled_char) {
+		/* second half of 10-databit bytesample */
+		st->buf32++;
+		ret |= (*(st->buf32) << (32 - st->bit_ofs));
+	}
+	st->bit_ofs = (st->bit_ofs + bits_per_sampled_char) % 32;
+
+	return ret & bytesample_mask;
+}
+
+static int nrzl_decode_sample(const u_int32_t sample, u_int8_t *data)
+{
+	*data = (sample >> 1) & 0xff;
+
+	if (!(sample & 0x01)) {
+		DEBUGPCRF("invalid start bit 0!");
+		return -EIO;
+	}
+	if (sample & 0x20) {
+		DEBUGPCRF("invalid stop bit 1!");
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static struct decoder_algo nrzl_decoder = {
+	.oversampling_rate = OVERSAMPLING_RATE,
+	.bits_per_sampled_char = 10 * OVERSAMPLING_RATE,
+	.bytesample_mask = 0x3ff,
+	.decode_sample = &nrzl_decode_sample,
+	.get_next_bytesample = &get_next_bytesample,
+};