1 files changed, 96 insertions, 0 deletions
diff --git a/src/fecmodem.cc b/src/fecmodem.cc
new file mode 100644
index 0000000..a75c27b
--- /dev/null
+++ b/src/fecmodem.cc
@@ -0,0 +1,96 @@
+/*
+ * 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>
+#include "fecmodem.h"
+
+uint8_t FECModem::parity128(uint8_t byte)
+{
+	return pgm_read_byte(&hammingParityLow[byte & 0x0f]) ^ pgm_read_byte(&hammingParityHigh[byte >> 4]);
+}
+
+uint8_t FECModem::parity2416(uint8_t byte1, uint8_t byte2)
+{
+	return parity128(byte1) | (parity128(byte2) << 4);
+}
+
+uint8_t FECModem::correct128(uint8_t *byte, uint8_t err)
+{
+	uint8_t result = pgm_read_byte(&hammingParityCheck[err & 0x0f]);
+
+	if (result != NO_ERROR) {
+		if (byte == NULL)
+			return 3;
+		if (result == UNCORRECTABLE) {
+			*byte = 0;
+			return 3;
+		}
+		if (result != ERROR_IN_PARITY) {
+			*byte ^= result;
+		}
+		return 1;
+	}
+	return 0;
+}
+
+uint8_t FECModem::hamming2416(uint8_t *byte1, uint8_t *byte2, uint8_t parity)
+{
+	uint8_t err;
+
+	if (byte1 == NULL || byte2 == NULL) {
+		return 3;
+	}
+
+	err = parity2416(*byte1, *byte2) ^ parity;
+
+	if (err) {
+		return correct128(byte1, err) + correct128(byte2, err >> 4);
+	}
+
+	return 0;
+}
+
+void FECModem::enable()
+{
+	this->Modem::enable();
+	hammingState = FIRST_BYTE;
+}
+
+uint8_t FECModem::buffer_available()
+{
+//   XXX this reset implementation is _completely_ broken
+//	if (newTransmission())
+//		hammingState = FIRST_BYTE;
+	if (this->Modem::buffer_available() >= 3)
+		return 2;
+	if (hammingState == SECOND_BYTE)
+		return 1;
+	return 0;
+}
+
+uint8_t FECModem::buffer_get()
+{
+	uint8_t byte1, parity;
+	if (hammingState == SECOND_BYTE) {
+		hammingState = FIRST_BYTE;
+		return buf_byte;
+	}
+	hammingState = SECOND_BYTE;
+	byte1 = this->Modem::buffer_get();
+	buf_byte = this->Modem::buffer_get();
+	parity = this->Modem::buffer_get();
+
+	hamming2416(&byte1, &buf_byte, parity);
+
+	return byte1;
+}
+
+FECModem modem;