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1 | 58d82c77 | Tom Mullins | /*
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2 | wiring.c - Partial implementation of the Wiring API for the ATmega8.
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3 | Part of Arduino - http://www.arduino.cc/
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4 | |||
5 | Copyright (c) 2005-2006 David A. Mellis
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6 | |||
7 | This library is free software; you can redistribute it and/or
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8 | modify it under the terms of the GNU Lesser General Public
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9 | License as published by the Free Software Foundation; either
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10 | version 2.1 of the License, or (at your option) any later version.
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11 | |||
12 | This library is distributed in the hope that it will be useful,
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13 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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15 | Lesser General Public License for more details.
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16 | |||
17 | You should have received a copy of the GNU Lesser General
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18 | Public License along with this library; if not, write to the
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19 | Free Software Foundation, Inc., 59 Temple Place, Suite 330,
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20 | Boston, MA 02111-1307 USA
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21 | |||
22 | $Id$
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23 | */
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24 | |||
25 | #include "wiring_private.h" |
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26 | |||
27 | // the prescaler is set so that timer0 ticks every 64 clock cycles, and the
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28 | // the overflow handler is called every 256 ticks.
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29 | #define MICROSECONDS_PER_TIMER0_OVERFLOW (clockCyclesToMicroseconds(64 * 256)) |
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30 | |||
31 | // the whole number of milliseconds per timer0 overflow
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32 | #define MILLIS_INC (MICROSECONDS_PER_TIMER0_OVERFLOW / 1000) |
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33 | |||
34 | // the fractional number of milliseconds per timer0 overflow. we shift right
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35 | // by three to fit these numbers into a byte. (for the clock speeds we care
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36 | // about - 8 and 16 MHz - this doesn't lose precision.)
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37 | #define FRACT_INC ((MICROSECONDS_PER_TIMER0_OVERFLOW % 1000) >> 3) |
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38 | #define FRACT_MAX (1000 >> 3) |
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39 | |||
40 | volatile unsigned long timer0_overflow_count = 0; |
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41 | volatile unsigned long timer0_millis = 0; |
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42 | static unsigned char timer0_fract = 0; |
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43 | |||
44 | #if defined(__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__)
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45 | SIGNAL(TIM0_OVF_vect) |
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46 | #else
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47 | SIGNAL(TIMER0_OVF_vect) |
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48 | #endif
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49 | { |
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50 | // copy these to local variables so they can be stored in registers
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51 | // (volatile variables must be read from memory on every access)
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52 | unsigned long m = timer0_millis; |
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53 | unsigned char f = timer0_fract; |
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54 | |||
55 | m += MILLIS_INC; |
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56 | f += FRACT_INC; |
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57 | if (f >= FRACT_MAX) {
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58 | f -= FRACT_MAX; |
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59 | m += 1;
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60 | } |
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61 | |||
62 | timer0_fract = f; |
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63 | timer0_millis = m; |
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64 | timer0_overflow_count++; |
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65 | } |
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66 | |||
67 | unsigned long millis() |
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68 | { |
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69 | unsigned long m; |
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70 | uint8_t oldSREG = SREG; |
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71 | |||
72 | // disable interrupts while we read timer0_millis or we might get an
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73 | // inconsistent value (e.g. in the middle of a write to timer0_millis)
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74 | cli(); |
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75 | m = timer0_millis; |
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76 | SREG = oldSREG; |
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77 | |||
78 | return m;
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79 | } |
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80 | |||
81 | unsigned long micros() { |
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82 | unsigned long m; |
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83 | uint8_t oldSREG = SREG, t; |
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84 | |||
85 | cli(); |
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86 | m = timer0_overflow_count; |
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87 | #if defined(TCNT0)
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88 | t = TCNT0; |
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89 | #elif defined(TCNT0L)
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90 | t = TCNT0L; |
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91 | #else
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92 | #error TIMER 0 not defined |
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93 | #endif
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94 | |||
95 | |||
96 | #ifdef TIFR0
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97 | if ((TIFR0 & _BV(TOV0)) && (t < 255)) |
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98 | m++; |
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99 | #else
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100 | if ((TIFR & _BV(TOV0)) && (t < 255)) |
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101 | m++; |
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102 | #endif
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103 | |||
104 | SREG = oldSREG; |
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105 | |||
106 | return ((m << 8) + t) * (64 / clockCyclesPerMicrosecond()); |
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107 | } |
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108 | |||
109 | void delay(unsigned long ms) |
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110 | { |
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111 | uint16_t start = (uint16_t)micros(); |
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112 | |||
113 | while (ms > 0) { |
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114 | if (((uint16_t)micros() - start) >= 1000) { |
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115 | ms--; |
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116 | start += 1000;
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117 | } |
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118 | } |
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119 | } |
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120 | |||
121 | /* Delay for the given number of microseconds. Assumes a 8 or 16 MHz clock. */
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122 | void delayMicroseconds(unsigned int us) |
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123 | { |
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124 | // calling avrlib's delay_us() function with low values (e.g. 1 or
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125 | // 2 microseconds) gives delays longer than desired.
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126 | //delay_us(us);
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127 | |||
128 | #if F_CPU >= 16000000L |
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129 | // for the 16 MHz clock on most Arduino boards
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130 | |||
131 | // for a one-microsecond delay, simply return. the overhead
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132 | // of the function call yields a delay of approximately 1 1/8 us.
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133 | if (--us == 0) |
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134 | return;
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135 | |||
136 | // the following loop takes a quarter of a microsecond (4 cycles)
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137 | // per iteration, so execute it four times for each microsecond of
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138 | // delay requested.
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139 | us <<= 2;
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140 | |||
141 | // account for the time taken in the preceeding commands.
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142 | us -= 2;
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143 | #else
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144 | // for the 8 MHz internal clock on the ATmega168
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145 | |||
146 | // for a one- or two-microsecond delay, simply return. the overhead of
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147 | // the function calls takes more than two microseconds. can't just
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148 | // subtract two, since us is unsigned; we'd overflow.
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149 | if (--us == 0) |
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150 | return;
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151 | if (--us == 0) |
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152 | return;
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153 | |||
154 | // the following loop takes half of a microsecond (4 cycles)
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155 | // per iteration, so execute it twice for each microsecond of
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156 | // delay requested.
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157 | us <<= 1;
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158 | |||
159 | // partially compensate for the time taken by the preceeding commands.
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160 | // we can't subtract any more than this or we'd overflow w/ small delays.
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161 | us--; |
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162 | #endif
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163 | |||
164 | // busy wait
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165 | __asm__ __volatile__ ( |
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166 | "1: sbiw %0,1" "\n\t" // 2 cycles |
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167 | "brne 1b" : "=w" (us) : "0" (us) // 2 cycles |
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168 | ); |
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169 | } |
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170 | |||
171 | void init()
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172 | { |
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173 | // this needs to be called before setup() or some functions won't
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174 | // work there
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175 | sei(); |
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176 | |||
177 | // on the ATmega168, timer 0 is also used for fast hardware pwm
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178 | // (using phase-correct PWM would mean that timer 0 overflowed half as often
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179 | // resulting in different millis() behavior on the ATmega8 and ATmega168)
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180 | #if defined(TCCR0A) && defined(WGM01)
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181 | sbi(TCCR0A, WGM01); |
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182 | sbi(TCCR0A, WGM00); |
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183 | #endif
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184 | |||
185 | // set timer 0 prescale factor to 64
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186 | #if defined(__AVR_ATmega128__)
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187 | // CPU specific: different values for the ATmega128
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188 | sbi(TCCR0, CS02); |
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189 | #elif defined(TCCR0) && defined(CS01) && defined(CS00)
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190 | // this combination is for the standard atmega8
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191 | sbi(TCCR0, CS01); |
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192 | sbi(TCCR0, CS00); |
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193 | #elif defined(TCCR0B) && defined(CS01) && defined(CS00)
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194 | // this combination is for the standard 168/328/1280/2560
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195 | sbi(TCCR0B, CS01); |
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196 | sbi(TCCR0B, CS00); |
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197 | #elif defined(TCCR0A) && defined(CS01) && defined(CS00)
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198 | // this combination is for the __AVR_ATmega645__ series
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199 | sbi(TCCR0A, CS01); |
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200 | sbi(TCCR0A, CS00); |
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201 | #else
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202 | #error Timer 0 prescale factor 64 not set correctly |
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203 | #endif
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204 | |||
205 | // enable timer 0 overflow interrupt
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206 | #if defined(TIMSK) && defined(TOIE0)
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207 | sbi(TIMSK, TOIE0); |
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208 | #elif defined(TIMSK0) && defined(TOIE0)
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209 | sbi(TIMSK0, TOIE0); |
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210 | #else
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211 | #error Timer 0 overflow interrupt not set correctly |
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212 | #endif
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213 | |||
214 | // timers 1 and 2 are used for phase-correct hardware pwm
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215 | // this is better for motors as it ensures an even waveform
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216 | // note, however, that fast pwm mode can achieve a frequency of up
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217 | // 8 MHz (with a 16 MHz clock) at 50% duty cycle
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218 | |||
219 | #if defined(TCCR1B) && defined(CS11) && defined(CS10)
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220 | TCCR1B = 0;
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221 | |||
222 | // set timer 1 prescale factor to 64
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223 | sbi(TCCR1B, CS11); |
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224 | #if F_CPU >= 8000000L |
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225 | sbi(TCCR1B, CS10); |
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226 | #endif
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227 | #elif defined(TCCR1) && defined(CS11) && defined(CS10)
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228 | sbi(TCCR1, CS11); |
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229 | #if F_CPU >= 8000000L |
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230 | sbi(TCCR1, CS10); |
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231 | #endif
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232 | #endif
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233 | // put timer 1 in 8-bit phase correct pwm mode
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234 | #if defined(TCCR1A) && defined(WGM10)
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235 | sbi(TCCR1A, WGM10); |
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236 | #elif defined(TCCR1)
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237 | #warning this needs to be finished
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238 | #endif
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239 | |||
240 | // set timer 2 prescale factor to 64
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241 | #if defined(TCCR2) && defined(CS22)
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242 | sbi(TCCR2, CS22); |
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243 | #elif defined(TCCR2B) && defined(CS22)
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244 | sbi(TCCR2B, CS22); |
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245 | #else
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246 | #warning Timer 2 not finished (may not be present on this CPU) |
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247 | #endif
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248 | |||
249 | // configure timer 2 for phase correct pwm (8-bit)
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250 | #if defined(TCCR2) && defined(WGM20)
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251 | sbi(TCCR2, WGM20); |
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252 | #elif defined(TCCR2A) && defined(WGM20)
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253 | sbi(TCCR2A, WGM20); |
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254 | #else
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255 | #warning Timer 2 not finished (may not be present on this CPU) |
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256 | #endif
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257 | |||
258 | #if defined(TCCR3B) && defined(CS31) && defined(WGM30)
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259 | sbi(TCCR3B, CS31); // set timer 3 prescale factor to 64
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260 | sbi(TCCR3B, CS30); |
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261 | sbi(TCCR3A, WGM30); // put timer 3 in 8-bit phase correct pwm mode
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262 | #endif
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263 | |||
264 | #if defined(TCCR4B) && defined(CS41) && defined(WGM40)
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265 | sbi(TCCR4B, CS41); // set timer 4 prescale factor to 64
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266 | sbi(TCCR4B, CS40); |
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267 | sbi(TCCR4A, WGM40); // put timer 4 in 8-bit phase correct pwm mode
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268 | #endif
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269 | |||
270 | #if defined(TCCR5B) && defined(CS51) && defined(WGM50)
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271 | sbi(TCCR5B, CS51); // set timer 5 prescale factor to 64
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272 | sbi(TCCR5B, CS50); |
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273 | sbi(TCCR5A, WGM50); // put timer 5 in 8-bit phase correct pwm mode
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274 | #endif
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275 | |||
276 | #if defined(ADCSRA)
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277 | // set a2d prescale factor to 128
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278 | // 16 MHz / 128 = 125 KHz, inside the desired 50-200 KHz range.
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279 | // XXX: this will not work properly for other clock speeds, and
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280 | // this code should use F_CPU to determine the prescale factor.
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281 | sbi(ADCSRA, ADPS2); |
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282 | sbi(ADCSRA, ADPS1); |
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283 | sbi(ADCSRA, ADPS0); |
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284 | |||
285 | // enable a2d conversions
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286 | sbi(ADCSRA, ADEN); |
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287 | #endif
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288 | |||
289 | // the bootloader connects pins 0 and 1 to the USART; disconnect them
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290 | // here so they can be used as normal digital i/o; they will be
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291 | // reconnected in Serial.begin()
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292 | #if defined(UCSRB)
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293 | UCSRB = 0;
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294 | #elif defined(UCSR0B)
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295 | UCSR0B = 0;
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296 | #endif
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297 | } |