Diff: AngleEncoder.cpp

Revision:

2:3771b3195c7b

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/AngleEncoder.cpp	Thu Oct 29 17:15:20 2015 +0000
@@ -0,0 +1,126 @@
+#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
+}