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1 //////////////////////////////////////////////////////////////////////////////
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2 // HISTORY
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3 // 2012-12-01 [jDG] Creation
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4 // 2012-12-23 [jDG] Added filtering.
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5 // 2012-12-30 [jDG] Added calibration (spherical best fit).
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6
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7 #include "compass.h"
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8
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9 //////////////////////////////////////////////////////////////////////////////
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10 // mH: Crude work-around, needs to be made right
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11 #ifndef UNIX
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12 # pragma udata overlay bank8=0x800
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13 static char C_STACK[256]; // Overlay C-code data stack here.
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14 # define RESET_C_STACK \
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15 _asm \
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16 LFSR 1, 0x800 \
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17 LFSR 2, 0x800 \
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18 _endasm
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19 # pragma udata overlay bank9_compass
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20 #else
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21 # define RESET_C_STACK
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22 #endif
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23
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24 //////////////////////////////////////////////////////////////////////////////
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25 // fifth order of polynomial approximation of atan(), giving 0.05 deg max error
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26 //
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27 #define K1 (5701) // Needs K1/2**16
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28 #define K2 (1645) // Needs K2/2**48 WAS NEGATIV
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29 #define K3 ( 446) // Needs K3/2**80
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30
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31 //////////////////////////////////////////////////////////////////////////////
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32 // Interface to assembleur multiplies
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33 Int16 umul(PARAMETER Int16 a, PARAMETER Int16 b)
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34 {
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35 extern Int16 compass_umul(void);
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36 extern Int16 compass_a, compass_b;
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37 compass_a = a;
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38 compass_b = b;
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39 return compass_umul();
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40 }
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41
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42 Int16 imul(PARAMETER Int16 a, PARAMETER Int16 b)
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43 {
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44 extern Int16 compass_imul(void);
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45 extern Int16 compass_a, compass_b;
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46 compass_a = a;
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47 compass_b = b;
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48 return compass_imul();
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49 }
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50
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51 //////////////////////////////////////////////////////////////////////////////
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52 /// Returns a / b * 2**16
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53 ///
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54 /// A 16/16 -> 16 bits divide, returning a scalled result.
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55 /// Used to multiply fractional numbers in the range 0..1,
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56 /// represented as 0..32767.
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57 Int16 udiv(PARAMETER Int16 a, PARAMETER Int16 b)
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58 {
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59 OVERLAY Int16 d, r;
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60
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61 //---- Pre-scale both numerator and denominator --------------------------
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62 while( (((a>>8) | (b>>8)) & 0xC0) == 0 )
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63 {
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64 a <<= 1;
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65 b <<= 1;
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66 }
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67
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68 //---- Make division trials ----------------------------------------------
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69 d = 0x4000; // Starts with 0.5, because 1.0 is sign bit.
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70 b >>= 1; // Hence pre-shift b.
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71 r = 0;
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72 do {
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73 if( a >= b ) { // a is big enough ?
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74 a -= b; // then count d times b out of it.
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75 r |= d; // and accumulate that bit.
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76 }
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77 b >>= 1; // then loop trying twice smaller.
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78 d >>= 1;
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79 } while( b );
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80 return r;
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81 }
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82
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83 //////////////////////////////////////////////////////////////////////////////
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84 /// Computes atan(y/x) in Angle, for x, y in range 0..32767
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85 ///
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86 /// Results a single quadrant Angle, in the range 0 .. Q_PI/2
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87 Angle utan(PARAMETER Int16 y, PARAMETER Int16 x)
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88 {
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89 OVERLAY Int16 ratio, angle, x2, x3;
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90
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91 //---- Handle zero divisor -----------------------------------------------
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92 if( x == 0 )
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93 return (y == 0) ? 0 : Q_PIO2;
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94
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95 //---- Make it half-quadrant : 0 .. 45 deg -------------------------------
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96 ratio = (x > y) ? udiv(y, x) : udiv(x, y);
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97
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98 //---- Then apply the polynomial approximation ---------------------------
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99 angle = umul(K1, ratio); // r*K1 / 2**16
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100 x2 = umul(ratio, ratio); // r**2 / 2**16
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101 x3 = umul(x2, ratio); // r**3 / 2**32
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102 angle -= umul(x3, K2); // K2*r**3 / 2**48: NEGATIV.
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103
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104 x3 = umul(x3, x2); // r**5 / 2**64
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105 angle += umul(x3, K3); // K3*r**5 / 2**80
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106
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107 //---- Recover the full quadrant -----------------------------------------
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108 return (x < y) ? (Angle)(Q_PIO2 - angle)
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109 : (Angle)(angle);
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110 }
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111
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112 //////////////////////////////////////////////////////////////////////////////
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113 /// Computes atan2(y/x) in Angle, for x, y in range -32768 to 32767
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114 ///
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115 /// Results a four quadrant Angle, in the range -Q_PI .. +Q_PI
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116 Angle itan(PARAMETER Int16 y, PARAMETER Int16 x)
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117 {
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118 // Beware: -32768 is not properly handled (sgn error).
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119 if( x == -32768 ) x = -32767;
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120 if( y == -32768 ) y = -32767;
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121
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122 if( x >= 0 )
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123 if( y >= 0 ) // First quadrant: 0..90 deg.
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124 return utan(y,x);
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125 else // Fourth quadrant: 0..-90 deg
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126 return -utan(-y,x);
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127 else
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128 if( y >= 0 ) // Second quadrant: 90..180 deg
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129 return Q_PI - utan(y, -x);
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130 else // Third quadrant: -90..-180 deg;
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131 return -Q_PI + utan(-y, -x);
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132 }
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133
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134 //////////////////////////////////////////////////////////////////////////////
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135 /// Computes cos(theta) = sqrtf(x2/h2),
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136 /// when theta = atan(y/x) and h2=x*x+y*y
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137 ///
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138 Int16 cosxh(PARAMETER Int16 x2, PARAMETER Int16 h2)
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139 {
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140 OVERLAY Int16 r = 0;
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141 OVERLAY Int16 d = 0x4000;
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142
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143 do {
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144 OVERLAY Int16 a = r + d;
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145 a = umul(a, a);
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146 a = umul(a, h2);
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147 if( a <= x2 ) r += d;
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148 d >>= 1;
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149 } while( d );
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150
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151 return r;
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152 }
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153
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154 //////////////////////////////////////////////////////////////////////////////
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155 /// Computes both sin and cos of angle y/x,
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156 /// with h = sqrt(x**2+y**2).
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157 ///
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158 void sincos(PARAMETER Int16 x, PARAMETER Int16 y, Int16* sin, Int16* cos)
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159 {
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160 OVERLAY Int16 x2, y2, h2;
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161
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162 //---- Fold into one quadant ---------------------------------------------
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163 OVERLAY char neg = 0;
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164 if( x < 0 )
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165 {
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166 neg |= 1;
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167 x = -x;
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168 }
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169 if( y < 0 )
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170 {
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171 neg |= 2;
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172 y = -y;
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173 }
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174
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175 //---- Pre-scale both numerator and denominator ----------------------
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176 while( (((x>>8) | (y>>8)) & 0xE0) == 0 )
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177 {
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178 x <<= 1;
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179 y <<= 1;
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180 }
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181
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182 //---- Uses trig() to do the stuff one on quadrant -------------------
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183 x2 = umul(x,x);
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184 y2 = umul(y,y);
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185 h2 = x2 + y2;
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186 x2 = cosxh(x2, h2);
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187
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188 //---- Results back in four quadrants --------------------------------
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189 *cos = (neg & 1) ? -x2 : x2;
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190 y2 = cosxh(y2, h2);
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191 *sin = (neg & 2) ? -y2 : y2;
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192 }
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193
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194 //////////////////////////////////////////////////////////////////////////////
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195 //
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196
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197 void compass(void)
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198 {
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199 OVERLAY Int16 sin, cos;
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200 OVERLAY Int16 iBfx, iBfy, Gz;
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201 OVERLAY Int16 iBpx, iBpy, iBpz;
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202 RESET_C_STACK;
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203
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204 //---- Make hard iron correction -----------------------------------------
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205 // Measured magnetometer orientation, measured ok.
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206 // From matthias drawing: (X,Y,Z) --> (X,Y,Z) : no rotation.
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207 iBpx = compass_DX_f - compass_CX_f; // X
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208 iBpy = compass_DY_f - compass_CY_f; // Y
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209 iBpz = compass_DZ_f - compass_CZ_f; // Z
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210
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211 //---- Calculate sine and cosine of roll angle Phi -----------------------
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212 sincos(accel_DZ_f, accel_DY_f, &sin, &cos);
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214
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213 // compass_roll = itan(sin, cos) / 100;
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214
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215 //---- rotate by roll angle (-Phi) ---------------------------------------
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216 iBfy = imul(iBpy, cos) - imul(iBpz, sin);
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217 iBpz = imul(iBpy, sin) + imul(iBpz, cos);
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218 Gz = imul(accel_DY_f, sin) + imul(accel_DZ_f, cos);
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219
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220 //---- calculate sin and cosine of pitch angle Theta ---------------------
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221 sincos(Gz, -accel_DX_f, &sin, &cos); // NOTE: changed sin sign.
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214
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222 // compass_pitch = itan(sin, cos) / 100;
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223
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224 /* correct cosine if pitch not in range -90 to 90 degrees */
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225 if( cos < 0 ) cos = -cos;
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226
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227 ///---- de-rotate by pitch angle Theta -----------------------------------
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228 iBfx = imul(iBpx, cos) + imul(iBpz, sin);
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229
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230 //---- Detect uncalibrated compass ---------------------------------------
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231 if( !compass_CX_f && !compass_CY_f && !compass_CZ_f )
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232 {
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233 compass_heading = -1;
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234 return;
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235 }
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236
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237 //---- calculate current yaw = e-compass angle Psi -----------------------
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238 // Result in degree (no need of 0.01 deg precision...
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239 compass_heading = itan(-iBfy, iBfx) / 100;
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240
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241 // Result in 0..360 range:
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242 if( compass_heading < 0 )
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243 compass_heading += 360;
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244 }
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