File content as of revision 2:3771b3195c7b:

#include "AngleEncoder.h"
#include "mbed.h"
 
AngleEncoder::AngleEncoder(PinName mosi, PinName miso, PinName sclk, PinName cs, int bits, int mode, int hz) :  
        _spi(mosi, miso, sclk), 
        _cs(cs) {
    // constructor
    _cs = 1;
    _spi.format(bits,mode);
    _spi.frequency(hz);
    
    wait_ms(1000); // Angle encoder requires 0.1 seconds to boot up, so I gave it an entire second.
    
}



/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 
 * 
 * Sends a NOP command.  This is a read command.
 *
 * Returns the 8 bit data read from the encoder.  
 *      0xA5 indicates communication is good, but no data to receive from encoder
 *      
 *      0x00 indicates that angle encoder probably wasn't read.  May need to 
 *      increase SPI_DELAY
 *  
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */ 
int AngleEncoder::nop() { // this function takes about 90us to complete (tested using Timer library)
    _cs = 0;
    wait_us(SPI_DELAY);
    int received = _spi.write(0x00);
    wait_us(SPI_DELAY);
    _cs = 1;
    wait_us(SPI_DELAY);
    return received;
}


/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 
 * 
 * Sets the current position as the zero point from which angles are calculated
 *  
 * Returns true if successful, false otherwise
 * 
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
bool AngleEncoder::set_zero() {
    char received;
    
    // send "set_zero_point" command
    _cs = 0;
    wait_us(SPI_DELAY);
    received = _spi.write(0x70); // send the command
    wait_us(SPI_DELAY);
    _cs = 1;
    wait_us(SPI_DELAY);
    
    // send NOP until reset is confirmed 
    while(received == 0xa5) received = nop();
    
    // 0x80 indicates that reset is confirmed
    if(received == 0x80) return true;
    else return false;
}


/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 
 * 
 *  Sets the current position as the zero point from which angles are calculated
 *  @param rotary_count  The address to the rotary_count variable, allowing this 
 *                       function to reset both the absolute and relative angles.
 *  
 *  Returns true if successful, false otherwise
 *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
bool AngleEncoder::set_zero(int* rotary_count) {
    
    *rotary_count = 0;  // reset relative counter
    return set_zero();  // reset absolute counter
}


/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 
 * 
 * Reads the absolute angle from the angle encoder via SPI
 * Returns the 12 bit angle (-2048, 2047)
 *  
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
int AngleEncoder::absolute_angle() { // this function takes about 500us to complete (tested using Timer library)
    char received;
    uint16_t absolute_pos;
    
    // send read command
    _cs = 0;
    wait_us(SPI_DELAY);
    received = _spi.write(0x10);
    wait_us(SPI_DELAY);
    _cs = 1;
    
    // wait for angle encoder to echo the command
    wait_us(SPI_DELAY);
    
    // read until encoder sends 0x10
    for(uint32_t i = 0; i < 100; i++)
    {
        received = nop();
        if(received == 0x10) break;
    }
    
    //while(received != 0x10) received = nop(); // read until 0x10 is received
        
    // the command should have been echoed back.  If so, then read the angle    
    if(received == 0x10)
    {
        // receive the most significatn 4 bits of the 12 bit angle
        absolute_pos = nop();  // read first 4 bits of absolute angle
        absolute_pos <<= 8; // shift the 4 bits into the right spot
        absolute_pos |= nop(); // receive the last 8 bits of absolute angle
        
        //make data symmetric around 0.
        //if(absolute_pos > 2048) absolute_pos -= 4096;
        //absolute_pos = ~absolute_pos + 1; // inverts the data
        return absolute_pos;
        }
    else return 0x00ff0000; // this is just a random number outside of the range of the encoder
}