Diff: main.cpp

Revision:

0:4347647932ee

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Mon Dec 29 16:18:23 2014 +0000
@@ -0,0 +1,105 @@
+#include "mbed.h"
+
+  PinName const SDA = PTE25;
+  PinName const SCL = PTE24;
+  
+  I2C i2c(SDA,SCL);
+
+#define REG_WHO_AM_I      0x0D
+#define REG_CTRL_REG_1    0x2A
+#define REG_OUT_X_MSB     0x01
+#define REG_OUT_Y_MSB     0x03
+#define REG_OUT_Z_MSB     0x05
+
+#define MMA8451_I2C_ADDRESS (0x1d<<1)
+
+// #define UINT14_MAX        16383
+#define UINT14_MAX        16384
+
+    PwmOut rled(LED_RED);
+    PwmOut gled(LED_GREEN);
+    PwmOut bled(LED_BLUE);
+
+static const float redx=0.0f;
+static const float redy=1.0f;
+static const float greenx=sqrt(3.0f)/2.0f;
+static const float greeny=-0.5f;
+static const float bluex=-sqrt(3.0f)/2.0f;
+static const float bluey=-0.5f;
+
+static const float twothirds=2.0f/3.0f;
+
+
+float acclnread(uint8_t reg)
+{
+  // Normalisation here seems wrong
+  char t[1]= {reg};
+  i2c.write(MMA8451_I2C_ADDRESS,t,1,true);
+  uint8_t xbits[2] = {0,0};
+  i2c.read(MMA8451_I2C_ADDRESS,(char *)xbits,2);
+  int16_t xint = 0;
+  xint=(xbits[0]<<6)|(xbits[1]>>2);
+  // this sign flip code looks wrong, UINT14_MAX maps to 0
+  // UINT14_MAX=16383, should it be UINT14_MAX=16384 
+  if (xint > UINT14_MAX>>1)
+    xint -= UINT14_MAX;
+  return float(xint)/4096.0f;
+  //  return float(xint);
+}
+
+int main(void)
+{
+  // initialise the accelerometer
+  {
+    uint8_t data[2] = {REG_CTRL_REG_1, 0x01};
+    i2c.write(MMA8451_I2C_ADDRESS,(char *)data,2);
+  }
+  
+  // read the who am i register
+  {
+    // this sets the pointer in the I2C decice (accelerometer)
+    // to point to the who_am_i register
+    char t[1] = {REG_WHO_AM_I};
+    i2c.write(MMA8451_I2C_ADDRESS,t,1,true);
+    // and this reads the register
+    uint8_t who_am_i = 0;
+    i2c.read(MMA8451_I2C_ADDRESS,(char *)&who_am_i,1);
+    printf("\r\nMMA8451 ID: %d\r\n", who_am_i );
+  }
+  // initially set leds off
+  rled=1.0f;
+  gled=1.0f;
+  bled=1.0f;
+  // 1ms pwm frequency
+  rled.period(0.001f);
+  gled.period(0.001f);
+  bled.period(0.001f);
+  
+  while (true) {
+
+    float xaccln,yaccln;
+    xaccln=acclnread(REG_OUT_X_MSB);
+    yaccln=acclnread(REG_OUT_Y_MSB);
+    float norm=sqrt(xaccln*xaccln + yaccln*yaccln);
+    float xacclnorm=xaccln/norm;
+    float yacclnorm=yaccln/norm;
+    
+    rled=twothirds*(1.0f-(xacclnorm*redx+yacclnorm*redy));
+    gled=twothirds*(1.0f-(xacclnorm*greenx+yacclnorm*greeny));
+    bled=twothirds*(1.0f-(xacclnorm*bluex+yacclnorm*bluey));
+    
+    //    rled = 1.0f + xaccln;
+    //    gled = 1.0f + yaccln;
+
+    printf("X: %1.4f, Y: %1.4f Norm: %1.4f R: %1.4f G: %1.4f B: %1.4f\r\n",
+	   xaccln, yaccln,
+	   norm,
+	   1.0f-rled.read(),1.0f-gled.read(),1.0f-bled.read());
+    wait(0.1f);
+    // sleep(); // keeps the pwm alive
+    // deepsleep(); // also keeps pwm alive
+    //  __WFI();
+
+  }
+}
+