Diff: main.cpp

Revision:

0:1f873630ed4f

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Thu Feb 07 12:18:49 2019 +0000
@@ -0,0 +1,98 @@
+#include "mbed.h"
+
+Serial pc(SERIAL_TX, SERIAL_RX);
+
+
+/* This example uses pins A0, A1 and A2 as SSC interface pins */
+DigitalOut SCK( A0 );
+DigitalInOut DATA( A2 );
+DigitalOut CSQ( A1 );
+
+
+
+/*Functions for bit level access to SSC bus */
+
+inline void ssc_write_bit( int value ){
+    SCK = 0;
+    wait_us(1);
+    SCK = 1;
+    wait_us(1);
+    if( value != 0 ){ DATA = 1; } else { DATA = 0; }
+    wait_us(1);
+    SCK = 0;
+    }
+
+inline int ssc_read_bit(){
+    int out = 0;
+    SCK = 0;
+    wait_us(1);
+    SCK = 1;
+    
+    wait_us(1);
+    SCK = 0;
+    if( DATA.read() != 0 ){ out = 1; }
+    
+    
+    return out;
+    }
+
+/* Functions to read & write 16bit words via SSC */
+
+void ssc_write_word( uint16_t word ){
+    DATA.output();
+    wait_us(1);
+    for( int i = 0; i < 16 ; ++i ){
+        ssc_write_bit( word & 0x8000 );
+        word <<= 1;
+        }
+    }
+
+uint16_t ssc_read_word(){
+    uint16_t word = 0;
+    DATA.input();
+    wait_us(1);
+    for( int i = 0; i < 16; ++i ){
+        word <<= 1;
+        word |= ssc_read_bit();
+        }
+   
+    return word; 
+    }
+
+/* And function to read angle from GMR sensor  */
+float encoder_read_angle(){
+    uint16_t data[2] = {10,10};
+    uint16_t cmd = 0x8000 | (2<<4) | 1;
+    float angle;
+    
+    /* Request new measurement */    
+    SCK = 0;
+    CSQ = 0;
+    wait_us(2);
+    CSQ = 1;
+    wait_us(2);
+    
+    /* Read angle register */
+    SCK = 0;
+    CSQ = 0;
+    ssc_write_word( cmd );
+    wait_us(2);
+    data[0] = ssc_read_word(); /* angle */
+    data[1] = ssc_read_word(); /* checksum */
+    CSQ = 1;
+    
+    /* compute angle from measurement */
+    angle = (0x7fff & data[0]) * 360.0f/(32768.0f);    
+    
+    return angle;
+    }
+
+int main() {
+    pc.baud( 115200 );
+    
+    while(1) {
+        float angle = encoder_read_angle();
+        pc.printf( "Angle: %.2f deg\r\n", angle );
+        wait( 0.25 );
+        }
+    }