From 917a7f7754e47567bf9102b6c26b6649ae6b28dd Mon Sep 17 00:00:00 2001
From: Josh Allen <axlecrusher@gmail.com>
Date: Fri, 10 Feb 2017 06:33:38 -0500
Subject: add initial ootx decoder

---
 tools/ootx_decode/ootx_decoder.c | 112 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 112 insertions(+)
 create mode 100644 tools/ootx_decode/ootx_decoder.c

(limited to 'tools/ootx_decode/ootx_decoder.c')

diff --git a/tools/ootx_decode/ootx_decoder.c b/tools/ootx_decode/ootx_decoder.c
new file mode 100644
index 0000000..70a88b5
--- /dev/null
+++ b/tools/ootx_decode/ootx_decoder.c
@@ -0,0 +1,112 @@
+// (C) 2016 Joshua Allen, MIT/x11 License.
+//
+//All MIT/x11 Licensed Code in this file may be relicensed freely under the GPL or LGPL licenses.
+
+/* ootx data decoder */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <assert.h>
+#include "ootx_decoder.h"
+
+//char* fmt_str = "L Y HMD %d 5 1 206230 %d\n";
+
+#define MAX_BUFF_SIZE 1024
+uint8_t* buffer = NULL;
+uint16_t buf_offset = 0;
+uint8_t bits_written = 0;
+uint16_t* payload_size = NULL;
+
+void (*ootx_packet_clbk)(ootx_packet* packet) = NULL;
+
+void ootx_init_buffer() {
+	buffer = (uint8_t*)malloc(MAX_BUFF_SIZE);
+	payload_size = (uint16_t*)buffer;
+	*payload_size = 0;
+}
+
+uint8_t ootx_decode_bit(uint32_t length) {
+	length = ((length/500)*500)+500;
+
+	length-=3000;
+	if (length>=2000) { length-=2000; }
+	if (length>=1000)  { return 0x01; }
+
+	return 0x00;
+}
+
+uint8_t ootx_detect_preamble(uint8_t dbit) {
+	static uint32_t preamble = 0x00;
+	preamble <<= 1;
+	preamble |= dbit;
+	if ((preamble & 0x0001ffff) == 0x01) return 1;
+	return 0;
+}
+
+void ootx_reset_buffer() {
+	buf_offset = 0;
+	buffer[buf_offset] = 0;
+	bits_written = 0;
+	*payload_size = 0;
+}
+
+void ootx_inc_buffer_offset() {
+	++buf_offset;
+//	if (buf_offset>=MAX_BUFF_SIZE) buf_offset = 0;
+	assert(buf_offset<MAX_BUFF_SIZE);
+	buffer[buf_offset] = 0;
+}
+
+void ootx_write_to_buffer(uint8_t dbit) {
+	uint8_t *current_byte = buffer+buf_offset;
+//	printf("%d\n", dbit);
+	*current_byte >>= 1;
+	*current_byte |= (0x80 * dbit);
+	++bits_written;
+	if (bits_written>7) {
+		bits_written=0;
+//		printf("%d\n", *current_byte);
+		ootx_inc_buffer_offset();
+	}
+}
+
+void ootx_process_bit(uint32_t length) {
+	static uint8_t bits_processed = 0;
+
+	uint8_t dbit = ootx_decode_bit(length);
+	++bits_processed;
+
+//	printf("z %d %d\n", bits_processed,dbit);
+//	printf("d %d\n", bits_processed,dbit);
+
+	if ( ootx_detect_preamble(dbit) ) {
+		/*	data stream can start over at any time so we must
+			always look for preamble bits */
+//		printf("Preamble found\n");
+		ootx_reset_buffer();
+		bits_processed = 0;
+	}
+	else if(bits_processed>16) {
+		//every 17th bit needs to be dropped
+//		printf("drop %d\n", dbit);
+		bits_processed = 0;
+	}
+	else
+	{
+		ootx_write_to_buffer(dbit);
+
+		if (buf_offset >= (*payload_size+6)) {
+			/*	once we have a complete ootx packet, send it out in the callback */
+			ootx_packet op;
+
+			op.length = *(uint16_t*)buffer;
+			op.data = buffer+2;
+			op.crc32 = *(uint32_t*)(buffer+2+op.length);
+			if (ootx_packet_clbk) ootx_packet_clbk(&op);
+
+			ootx_reset_buffer();
+		}
+	}
+}
+
-- 
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