1 files changed, 67 insertions, 0 deletions
diff --git a/src/fecmodem.h b/src/fecmodem.h
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+++ b/src/fecmodem.h
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+/*
+ * Copyright (C) 2016 by Daniel Friesel
+ *
+ * License: You may use, redistribute and/or modify this file under the terms
+ * of either:
+ * * The GNU LGPL v3 (see COPYING and COPYING.LESSER), or
+ * * The 3-clause BSD License (see COPYING.BSD)
+ *
+ */
+
+#include <avr/io.h>
+#include <stdlib.h>
+
+#ifndef FECMODEM_H_
+#define FECMODEM_H_
+
+#include "hamming.h"
+#include "modem.h"
+
+/**
+ * Receive-only modem with forward error correction.
+ * Uses the Modem class to read raw modem data and uses the Hamming 2416
+ * algorithm to detect and, if possible, correct transmission errors.
+ * Exposes a global modem object for convenience.
+ */
+class FECModem : public Modem {
+	private:
+		enum HammingState : uint8_t {
+			FIRST_BYTE,
+			SECOND_BYTE
+		};
+		HammingState hammingState;
+		uint8_t buf_byte;
+
+		uint8_t parity128(uint8_t byte);
+		uint8_t parity2416(uint8_t byte1, uint8_t byte2);
+		uint8_t correct128(uint8_t *byte, uint8_t parity);
+		uint8_t hamming2416(uint8_t *byte1, uint8_t *byte2, uint8_t parity);
+	public:
+		FECModem() : Modem() {};
+
+		/**
+		 * Enable the modem. Resets the internal Hamming state and calls
+		 * Modem::enable().
+		 */
+		void enable(void);
+
+		/**
+		 * Checks if there are unprocessed bytes in the receive buffer.
+		 * Parity bytes are accounted for, so if three raw bytes (two data,
+		 * one parity) were received by Modem::receive(), this function will
+		 * return 2.
+		 * @return number of unprocessed data bytes
+		 */
+		uint8_t buffer_available(void);
+
+		/**
+		 * Get next byte from the receive buffer.
+		 * @return received byte (0 if it contained uncorrectable errors
+		 *         or the buffer is empty)
+		 */
+		uint8_t buffer_get(void);
+};
+
+extern FECModem modem;
+
+#endif /* FECMODEM_H_ */