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 * 1. Redistributions of source code must retain the above copyright
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 *    used to endorse or promote products derived from this software
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/*
 * @file sumd.h
 *
 * RC protocol definition for Graupner HoTT transmitter (SUMD/SUMH Protocol)
 *
 * @author Marco Bauer <marco@wtns.de>
 */

#include <stdbool.h>
#include <stdio.h>
#include "sumd.h"


enum SUMD_DECODE_STATE {
	SUMD_DECODE_STATE_UNSYNCED = 0,
	SUMD_DECODE_STATE_GOT_HEADER,
	SUMD_DECODE_STATE_GOT_STATE,
	SUMD_DECODE_STATE_GOT_LEN,
	SUMD_DECODE_STATE_GOT_DATA,
	SUMD_DECODE_STATE_GOT_CRC,
	SUMD_DECODE_STATE_GOT_CRC16_BYTE_1,
	SUMD_DECODE_STATE_GOT_CRC16_BYTE_2
};

/*
const char *decode_states[] = {"UNSYNCED",
			       "GOT_HEADER",
			       "GOT_STATE",
			       "GOT_LEN",
			       "GOT_DATA",
			       "GOT_CRC",
			       "GOT_CRC16_BYTE_1",
			       "GOT_CRC16_BYTE_2"
			      };
*/

uint8_t 	_crc8 	= 0x00;
uint16_t 	_crc16 = 0x0000;
bool 		_sumd 		= true;
bool		_crcOK		= false;
bool		_debug		= false;


/* define range mapping here, -+100% -> 1000..2000 */
#define SUMD_RANGE_MIN 0.0f
#define SUMD_RANGE_MAX 4096.0f

#define SUMD_TARGET_MIN 1000.0f
#define SUMD_TARGET_MAX 2000.0f

/* pre-calculate the floating point stuff as far as possible at compile time */
#define SUMD_SCALE_FACTOR ((SUMD_TARGET_MAX - SUMD_TARGET_MIN) / (SUMD_RANGE_MAX - SUMD_RANGE_MIN))
#define SUMD_SCALE_OFFSET (int)(SUMD_TARGET_MIN - (SUMD_SCALE_FACTOR * SUMD_RANGE_MIN + 0.5f))

static enum SUMD_DECODE_STATE _decode_state = SUMD_DECODE_STATE_UNSYNCED;
static uint8_t _rxlen;

static ReceiverFcPacketHoTT _rxpacket;


uint16_t sumd_crc16(uint16_t crc, uint8_t value)
{
	int i;
	crc ^= (uint16_t)value << 8;
	for (i = 0; i < 8; i++) {
		crc = (crc & 0x8000) ? (crc << 1) ^ 0x1021 : (crc << 1);
	}
	return crc;
}

uint8_t sumd_crc8(uint8_t crc, uint8_t value)
{
	crc += value;
	return crc;
}

int sumd_decode(uint8_t byte, uint8_t *rssi, uint8_t *rx_count, uint16_t *channel_count, uint16_t *channels,
		    uint16_t max_chan_count)
{

	int ret = 1;
	switch (_decode_state) {
	case SUMD_DECODE_STATE_UNSYNCED:
		if(_debug)
			printf( " SUMD_DECODE_STATE_UNSYNCED \n") ;
			
		if (byte == SUMD_HEADER_ID) {
			_rxpacket.header = byte;
			_sumd = true;
			_rxlen = 0;
			_crc16 = 0x0000;
			_crc8 = 0x00;
			_crcOK = false;
			_crc16 = sumd_crc16(_crc16, byte);
			_crc8 = sumd_crc8(_crc8, byte);
			_decode_state = SUMD_DECODE_STATE_GOT_HEADER;
			if(_debug)
				printf( " SUMD_DECODE_STATE_GOT_HEADER: %x \n", byte) ;
				
		} else {
			ret = 3;
		}

		break;

	case SUMD_DECODE_STATE_GOT_HEADER:
		if (byte == SUMD_ID_SUMD || byte == SUMD_ID_SUMH) {
			_rxpacket.status = byte;
			if (byte == SUMD_ID_SUMH) {
				_sumd = false;
			}
			if (_sumd) {
				_crc16 = sumd_crc16(_crc16, byte);
			} else {
				_crc8 = sumd_crc8(_crc8, byte);	
			}
			_decode_state = SUMD_DECODE_STATE_GOT_STATE;
			if(_debug)
				printf( " SUMD_DECODE_STATE_GOT_STATE: %x \n", byte) ;

		} else {
			_decode_state = SUMD_DECODE_STATE_UNSYNCED;
		}

		break;

	case SUMD_DECODE_STATE_GOT_STATE:
		if (byte >= 2 && byte <= SUMD_MAX_CHANNELS) {
			_rxpacket.length = byte;
			if (_sumd) {
				_crc16 = sumd_crc16(_crc16, byte);
			} else {
				_crc8 = sumd_crc8(_crc8, byte);	
			}
			_rxlen++;
			_decode_state = SUMD_DECODE_STATE_GOT_LEN;
			if(_debug)
				printf( " SUMD_DECODE_STATE_GOT_LEN: %x (%d) \n", byte, byte) ;
				
		} else {
			_decode_state = SUMD_DECODE_STATE_UNSYNCED;
		}
		break;

	case SUMD_DECODE_STATE_GOT_LEN:
		_rxpacket.sumd_data[_rxlen] = byte;
		if (_sumd) {
			_crc16 = sumd_crc16(_crc16, byte);
		} else {
			_crc8 = sumd_crc8(_crc8, byte);	
		}
		_rxlen++;
		
		if (_rxlen <= ((_rxpacket.length*2) )) {
			if(_debug)
				printf( " SUMD_DECODE_STATE_GOT_DATA[%d]: %x\n", _rxlen-2, byte) ;

		} else {
			_decode_state = SUMD_DECODE_STATE_GOT_DATA;
			if(_debug)
				printf( " SUMD_DECODE_STATE_GOT_DATA -- finish --\n") ;
				
		}

		break;

	case SUMD_DECODE_STATE_GOT_DATA:
		_rxpacket.crc16_high = byte;
		if(_debug)
			printf( " SUMD_DECODE_STATE_GOT_CRC16[1]: %x   [%x]\n", byte, ((_crc16 >> 8) & 0xff)) ;
			
		if (_sumd) {
			_decode_state = SUMD_DECODE_STATE_GOT_CRC;
		} else {
			_decode_state = SUMD_DECODE_STATE_GOT_CRC16_BYTE_1;
		}

		break;

	case SUMD_DECODE_STATE_GOT_CRC16_BYTE_1:
		_rxpacket.crc16_low = byte;
		if(_debug)
			printf( " SUMD_DECODE_STATE_GOT_CRC16[2]: %x   [%x]\n", byte, (_crc16 & 0xff)) ;
			
		_decode_state = SUMD_DECODE_STATE_GOT_CRC16_BYTE_2;

		break;

	case SUMD_DECODE_STATE_GOT_CRC16_BYTE_2:
		_rxpacket.telemetry = byte;
		if(_debug)
			printf( " SUMD_DECODE_STATE_GOT_SUMH_TELEMETRY: %x\n", byte) ;
			
		_decode_state = SUMD_DECODE_STATE_GOT_CRC;

		break;
		
	case SUMD_DECODE_STATE_GOT_CRC:
		if (_sumd) {
			_rxpacket.crc16_low = byte;
			if(_debug)
				printf( " SUMD_DECODE_STATE_GOT_CRC[2]: %x   [%x]\n\n", byte, (_crc16 & 0xff)) ;
				
			if (_crc16 == (uint16_t)(_rxpacket.crc16_high<<8)+_rxpacket.crc16_low) {
				_crcOK = true;
			}
		} else {
			_rxpacket.crc8 = byte;
			if(_debug)
				printf( " SUMD_DECODE_STATE_GOT_CRC8_SUMH: %x   [%x]\n\n", byte, _crc8) ;
				
			if (_crc8 == _rxpacket.crc8) {
				_crcOK = true;
			}
		}
		
		if (_crcOK) {
			if(_debug)
				printf( " CRC - OK \n") ;

			if (_sumd) {
				if(_debug)
					printf( " Got valid SUMD Packet\n") ;
					
			} else {
				if(_debug)
					printf( " Got valid SUMH Packet\n") ;
					
			}
			
			if(_debug)
				printf( " RXLEN: %d  [Chans: %d] \n\n", _rxlen-1, (_rxlen-1)/2) ;

			ret = 0;
			unsigned i;
			uint8_t _cnt = *rx_count + 1;
			*rx_count = _cnt;
		
			*rssi = 255;

			/* received Channels */
			if ((uint16_t)_rxpacket.length > max_chan_count) {
				_rxpacket.length = (uint8_t) max_chan_count;
			}
			*channel_count = (uint16_t)_rxpacket.length;

			/* decode the actual packet */
			/* reorder first 4 channels */

			/* ch1 = roll -> sumd = ch2 */
			channels[0] = (uint16_t)((_rxpacket.sumd_data[1*2+1]<<8) | _rxpacket.sumd_data[1*2+2])>>3;
			/* ch2 = pitch -> sumd = ch2 */
			channels[1] = (uint16_t)((_rxpacket.sumd_data[2*2+1]<<8) | _rxpacket.sumd_data[2*2+2])>>3;
			/* ch3 = throttle -> sumd = ch2 */
			channels[2] = (uint16_t)((_rxpacket.sumd_data[0*2+1]<<8) | _rxpacket.sumd_data[0*2+2])>>3;
			/* ch4 = yaw -> sumd = ch2 */
			channels[3] = (uint16_t)((_rxpacket.sumd_data[3*2+1]<<8) | _rxpacket.sumd_data[3*2+2])>>3;

			/* we start at channel 5(index 4) */
			unsigned chan_index = 4;

			for (i = 4; i < _rxpacket.length; i++) {
				if(_debug)
					printf( "ch[%d] : %x %x [ %x    %d ]\n", i+1, _rxpacket.sumd_data[i*2+1], _rxpacket.sumd_data[i*2+2], ((_rxpacket.sumd_data[i*2+1]<<8) | _rxpacket.sumd_data[i*2+2])>>3, ((_rxpacket.sumd_data[i*2+1]<<8) | _rxpacket.sumd_data[i*2+2])>>3);
					
				channels[chan_index] = (uint16_t)((_rxpacket.sumd_data[i*2+1]<<8) | _rxpacket.sumd_data[i*2+2])>>3;
				/* convert values to 1000-2000 ppm encoding in a not too sloppy fashion */
				//channels[chan_index] = (uint16_t)(channels[chan_index] * SUMD_SCALE_FACTOR + .5f) + SUMD_SCALE_OFFSET;

				chan_index++;
			}

		} else {
			/* decoding failed */
			ret = 4;
			if(_debug)
				printf( " CRC - fail \n") ;

		}

		_decode_state = SUMD_DECODE_STATE_UNSYNCED;
		break;
	}

	return ret;
}