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1 //////////////////////////////////////////////////////////////////////////////
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2 /// compass.c
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3 /// Compute north direction from magnetic/acceleration measures.
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4 /// Copyright (c) 2012-2015, JD Gascuel, HeinrichsWeikamp, all right reserved.
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5 //////////////////////////////////////////////////////////////////////////////
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6 // HISTORY
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7 // 2012-12-01 [jDG] Creation
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8 // 2012-12-23 [jDG] Added filtering.
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9 // 2012-12-30 [jDG] Added calibration (spherical best fit).
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282
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10 // 2015-05-22 [jDG] Minor cleanups. Smaller calibration code.
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11
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12 #include "compass.h"
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13
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14 //////////////////////////////////////////////////////////////////////////////
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15 // mH: Crude work-around, needs to be made right
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16 #ifndef UNIX
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17 # pragma udata overlay bank8=0x800
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18 static char C_STACK[256]; // Overlay C-code data stack here.
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19 # define RESET_C_STACK \
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20 _asm \
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21 LFSR 1, 0x800 \
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22 LFSR 2, 0x800 \
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23 _endasm
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24 # pragma udata overlay bank9_compass
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282
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25 # pragma code compass_run
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26 #else
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282
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27 # define RESET_C_STACK
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0
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28 #endif
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29
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30 //////////////////////////////////////////////////////////////////////////////
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31 // fifth order of polynomial approximation of atan(), giving 0.05 deg max error
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32 //
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33 #define K1 (5701) // Needs K1/2**16
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34 #define K2 (1645) // Needs K2/2**48 WAS NEGATIV
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35 #define K3 ( 446) // Needs K3/2**80
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36
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37 //////////////////////////////////////////////////////////////////////////////
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38 // Interface to assembleur multiplies
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39 Int16 umul(PARAMETER Int16 a, PARAMETER Int16 b)
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40 {
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41 extern Int16 compass_umul(void);
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42 extern Int16 compass_a, compass_b;
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43 compass_a = a;
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44 compass_b = b;
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45 return compass_umul();
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46 }
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47
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48 Int16 imul(PARAMETER Int16 a, PARAMETER Int16 b)
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49 {
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50 extern Int16 compass_imul(void);
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51 extern Int16 compass_a, compass_b;
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52 compass_a = a;
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53 compass_b = b;
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54 return compass_imul();
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55 }
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56
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57 //////////////////////////////////////////////////////////////////////////////
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58 /// Returns a / b * 2**16
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59 ///
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60 /// A 16/16 -> 16 bits divide, returning a scalled result.
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61 /// Used to multiply fractional numbers in the range 0..1,
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62 /// represented as 0..32767.
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63 Int16 udiv(PARAMETER Int16 a, PARAMETER Int16 b)
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64 {
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65 OVERLAY Int16 d, r;
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66
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67 //---- Pre-scale both numerator and denominator --------------------------
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68 while( (((a>>8) | (b>>8)) & 0xC0) == 0 )
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69 {
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70 a <<= 1;
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71 b <<= 1;
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72 }
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73
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74 //---- Make division trials ----------------------------------------------
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75 d = 0x4000; // Starts with 0.5, because 1.0 is sign bit.
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76 b >>= 1; // Hence pre-shift b.
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77 r = 0;
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78 do {
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79 if( a >= b ) { // a is big enough ?
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80 a -= b; // then count d times b out of it.
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81 r |= d; // and accumulate that bit.
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82 }
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83 b >>= 1; // then loop trying twice smaller.
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84 d >>= 1;
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85 } while( b );
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86 return r;
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87 }
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88
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89 //////////////////////////////////////////////////////////////////////////////
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90 /// Computes atan(y/x) in Angle, for x, y in range 0..32767
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91 ///
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92 /// Results a single quadrant Angle, in the range 0 .. Q_PI/2
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93 Angle utan(PARAMETER Int16 y, PARAMETER Int16 x)
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94 {
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95 OVERLAY Int16 ratio, angle, x2, x3;
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96
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97 //---- Handle zero divisor -----------------------------------------------
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98 if( x == 0 )
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99 return (y == 0) ? 0 : Q_PIO2;
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100
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101 //---- Make it half-quadrant : 0 .. 45 deg -------------------------------
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102 ratio = (x > y) ? udiv(y, x) : udiv(x, y);
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103
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104 //---- Then apply the polynomial approximation ---------------------------
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105 angle = umul(K1, ratio); // r*K1 / 2**16
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106 x2 = umul(ratio, ratio); // r**2 / 2**16
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107 x3 = umul(x2, ratio); // r**3 / 2**32
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108 angle -= umul(x3, K2); // K2*r**3 / 2**48: NEGATIV.
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109
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110 x3 = umul(x3, x2); // r**5 / 2**64
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111 angle += umul(x3, K3); // K3*r**5 / 2**80
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112
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113 //---- Recover the full quadrant -----------------------------------------
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114 return (x < y) ? (Angle)(Q_PIO2 - angle)
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115 : (Angle)(angle);
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116 }
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117
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118 //////////////////////////////////////////////////////////////////////////////
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119 /// Computes atan2(y/x) in Angle, for x, y in range -32768 to 32767
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120 ///
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121 /// Results a four quadrant Angle, in the range -Q_PI .. +Q_PI
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122 Angle itan(PARAMETER Int16 y, PARAMETER Int16 x)
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123 {
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124 // Beware: -32768 is not properly handled (sgn error).
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125 if( x == -32768 ) x = -32767;
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126 if( y == -32768 ) y = -32767;
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127
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128 if( x >= 0 )
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129 if( y >= 0 ) // First quadrant: 0..90 deg.
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130 return utan(y,x);
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131 else // Fourth quadrant: 0..-90 deg
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132 return -utan(-y,x);
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133 else
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134 if( y >= 0 ) // Second quadrant: 90..180 deg
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135 return Q_PI - utan(y, -x);
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136 else // Third quadrant: -90..-180 deg;
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137 return -Q_PI + utan(-y, -x);
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138 }
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139
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140 //////////////////////////////////////////////////////////////////////////////
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141 /// Computes cos(theta) = sqrtf(x2/h2),
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142 /// when theta = atan(y/x) and h2=x*x+y*y
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143 ///
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144 Int16 cosxh(PARAMETER Int16 x2, PARAMETER Int16 h2)
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145 {
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146 OVERLAY Int16 r = 0;
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147 OVERLAY Int16 d = 0x4000;
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148
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149 do {
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150 OVERLAY Int16 a = r + d;
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151 a = umul(a, a);
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152 a = umul(a, h2);
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153 if( a <= x2 ) r += d;
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154 d >>= 1;
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155 } while( d );
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156
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157 return r;
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158 }
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159
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160 //////////////////////////////////////////////////////////////////////////////
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161 /// Computes both sin and cos of angle y/x,
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162 /// with h = sqrt(x**2+y**2).
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163 ///
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164 void sincos(PARAMETER Int16 x, PARAMETER Int16 y, Int16* sin, Int16* cos)
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165 {
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166 OVERLAY Int16 x2, y2, h2;
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167
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168 //---- Fold into one quadant ---------------------------------------------
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169 OVERLAY char neg = 0;
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170 if( x < 0 )
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171 {
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172 neg |= 1;
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173 x = -x;
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174 }
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175 if( y < 0 )
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176 {
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177 neg |= 2;
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178 y = -y;
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179 }
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180
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181 //---- Pre-scale both numerator and denominator ----------------------
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182 while( (((x>>8) | (y>>8)) & 0xE0) == 0 )
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183 {
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184 x <<= 1;
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185 y <<= 1;
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186 }
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187
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188 //---- Uses trig() to do the stuff one on quadrant -------------------
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189 x2 = umul(x,x);
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190 y2 = umul(y,y);
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191 h2 = x2 + y2;
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192 x2 = cosxh(x2, h2);
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193
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194 //---- Results back in four quadrants --------------------------------
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195 *cos = (neg & 1) ? -x2 : x2;
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196 y2 = cosxh(y2, h2);
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197 *sin = (neg & 2) ? -y2 : y2;
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198 }
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199
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200 //////////////////////////////////////////////////////////////////////////////
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201 //
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202
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203 void compass(void)
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204 {
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205 OVERLAY Int16 sin, cos;
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206 OVERLAY Int16 iBfx, iBfy, Gz;
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207 OVERLAY Int16 iBpx, iBpy, iBpz;
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208 RESET_C_STACK;
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209
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210 //---- Make hard iron correction -----------------------------------------
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211 // Measured magnetometer orientation, measured ok.
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212 // From matthias drawing: (X,Y,Z) --> (X,Y,Z) : no rotation.
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213 iBpx = compass_DX_f - compass_CX_f; // X
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214 iBpy = compass_DY_f - compass_CY_f; // Y
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215 iBpz = compass_DZ_f - compass_CZ_f; // Z
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216
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217 //---- Calculate sine and cosine of roll angle Phi -----------------------
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218 sincos(accel_DZ_f, accel_DY_f, &sin, &cos);
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219
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220 //---- rotate by roll angle (-Phi) ---------------------------------------
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221 iBfy = imul(iBpy, cos) - imul(iBpz, sin);
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222 iBpz = imul(iBpy, sin) + imul(iBpz, cos);
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223 Gz = imul(accel_DY_f, sin) + imul(accel_DZ_f, cos);
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224
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225 //---- calculate sin and cosine of pitch angle Theta ---------------------
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226 sincos(Gz, -accel_DX_f, &sin, &cos); // NOTE: changed sin sign.
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227
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228 /* correct cosine if pitch not in range -90 to 90 degrees */
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229 if( cos < 0 ) cos = -cos;
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230
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231 ///---- de-rotate by pitch angle Theta -----------------------------------
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232 iBfx = imul(iBpx, cos) + imul(iBpz, sin);
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233
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234 //---- Detect uncalibrated compass ---------------------------------------
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235 if( !compass_CX_f && !compass_CY_f && !compass_CZ_f )
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236 {
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237 compass_heading = -1;
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238 return;
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239 }
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240
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241 //---- calculate current yaw = e-compass angle Psi -----------------------
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242 // Result in degree (no need of 0.01 deg precision...
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243 compass_heading = itan(-iBfy, iBfx) / 100;
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244
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245 // Result in 0..360 range:
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246 if( compass_heading < 0 )
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247 compass_heading += 360;
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248 }
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