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Revision 674

Wrote encoders.c and encoders.h Would GREATLY appreciate it if someone could check if I got the receive function correct. There was a lot of bit twiddling. Useful
functions still need to be written, however receiving raw encoder readings should work (not tested... so don't bet on it)

View differences:

encoders.c
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#include "encoders.h"
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#include "spi.h"
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#include <dragonfly_lib.h>
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//Dummy file for now.
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void encoder_recv(char data);
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unsigned short int left_data_buf;
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unsigned short int right_data_buf;
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char buf_index;
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unsigned short int left_data;
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unsigned short int right_data;
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void encoders_init(void){
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	spi_init(encoder_recv);
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	buf_index = 0;
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	left_data_buf = 0;
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	right_data_buf= 0;
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	left_data = -1;
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	right_data = -1;
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}
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int encoder_read(char encoder){
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	if(encoder==LEFT)
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		return left_data;
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	else if(encoder==RIGHT)
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		return right_data;
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	else return -1;
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}
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int encoder_change(char encoder){
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	return 0;
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}
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char encoder_direction(char encoder){
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	return 0;
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}
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//Full reads occur every 40 microseconds. This function should be called
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//every 8 microseconds.
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void encoder_recv(char data){
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	if(buf_index < 2)
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		right_data_buf |= (((short)data) << ((1-buf_index)*8)) & (0xF<<(1-buf_index));
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	else if (buf_index == 2)
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		left_data_buf |= (((short)data) << 9) & (0x7F << 9);
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	else if (buf_index == 3)
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		left_data_buf |= ((short)(data) << 1) & (0xFF<<1);
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	else if (buf_index == 4)
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		left_data_buf |= (data>>7) & 0x1;
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	buf_index = (buf_index + 1) % 5;
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	if(buf_index==0){
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		if(left_data_buf & (OCF | COF | LIN)) 
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			left_data = INVALID;
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		else if(((left_data_buf & MagINCn) > 0)  && ((left_data_buf & MagDECn) > 0)) 
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			left_data = MAGNET_FAILURE;
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		else left_data = (left_data_buf>>5) & 1023;
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		if(right_data_buf & (OCF | COF | LIN)) 
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			right_data = INVALID;
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		else if ( ((left_data_buf & MagINCn) > 0)  && ((left_data_buf & MagDECn) > 0)) 
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			left_data = MAGNET_FAILURE;
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		else right_data = (right_data_buf>>5) & 1023;
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		left_data_buf = 0;
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		right_data_buf = 0;
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	}
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}

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