Pat Hickey
12 years ago
committed by
Andrew Tridgell
4 changed files with 189 additions and 162 deletions
@ -0,0 +1,161 @@
@@ -0,0 +1,161 @@
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#include <avr/io.h> |
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#include <avr/interrupt.h> |
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#include "HAL_AVR.h" |
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#include "Scheduler.h" |
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using namespace AP_HAL_AVR; |
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#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit)) |
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#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit)) |
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static volatile uint32_t timer0_overflow_count = 0; |
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static volatile uint32_t timer0_millis = 0; |
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static uint8_t timer0_fract = 0; |
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void AVRTimer::init() { |
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// this needs to be called before setup() or some functions won't
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// work there
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sei(); |
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// set timer 0 prescale factor to 64
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// this combination is for the standard 168/328/1280/2560
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sbi(TCCR0B, CS01); |
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sbi(TCCR0B, CS00); |
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// enable timer 0 overflow interrupt
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sbi(TIMSK0, TOIE0); |
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// timers 1 and 2 are used for phase-correct hardware pwm
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// this is better for motors as it ensures an even waveform
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// note, however, that fast pwm mode can achieve a frequency of up
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// 8 MHz (with a 16 MHz clock) at 50% duty cycle
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TCCR1B = 0; |
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// set timer 1 prescale factor to 64
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sbi(TCCR1B, CS11); |
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sbi(TCCR1B, CS10); |
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// put timer 1 in 8-bit phase correct pwm mode
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sbi(TCCR1A, WGM10); |
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sbi(TCCR3B, CS31); // set timer 3 prescale factor to 64
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sbi(TCCR3B, CS30); |
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sbi(TCCR3A, WGM30); // put timer 3 in 8-bit phase correct pwm mode
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sbi(TCCR4B, CS41); // set timer 4 prescale factor to 64
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sbi(TCCR4B, CS40); |
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sbi(TCCR4A, WGM40); // put timer 4 in 8-bit phase correct pwm mode
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sbi(TCCR5B, CS51); // set timer 5 prescale factor to 64
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sbi(TCCR5B, CS50); |
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sbi(TCCR5A, WGM50); // put timer 5 in 8-bit phase correct pwm mode
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// set a2d prescale factor to 128
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// 16 MHz / 128 = 125 KHz, inside the desired 50-200 KHz range.
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// XXX: this will not work properly for other clock speeds, and
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// this code should use F_CPU to determine the prescale factor.
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sbi(ADCSRA, ADPS2); |
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sbi(ADCSRA, ADPS1); |
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sbi(ADCSRA, ADPS0); |
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// enable a2d conversions
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sbi(ADCSRA, ADEN); |
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// the bootloader connects pins 0 and 1 to the USART; disconnect them
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// here so they can be used as normal digital i/o; they will be
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// reconnected in Serial.begin()
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UCSR0B = 0; |
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} |
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#define clockCyclesPerMicrosecond() ( F_CPU / 1000000L ) |
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#define clockCyclesToMicroseconds(a) ( ((a) * 1000L) / (F_CPU / 1000L) ) |
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// the prescaler is set so that timer0 ticks every 64 clock cycles, and the
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// the overflow handler is called every 256 ticks.
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#define MICROSECONDS_PER_TIMER0_OVERFLOW (clockCyclesToMicroseconds(64 * 256)) |
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// the whole number of milliseconds per timer0 overflow
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#define MILLIS_INC (MICROSECONDS_PER_TIMER0_OVERFLOW / 1000) |
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// the fractional number of milliseconds per timer0 overflow. we shift right
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// by three to fit these numbers into a byte. (for the clock speeds we care
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// about - 8 and 16 MHz - this doesn't lose precision.)
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#define FRACT_INC ((MICROSECONDS_PER_TIMER0_OVERFLOW % 1000) >> 3) |
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#define FRACT_MAX (1000 >> 3) |
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SIGNAL(TIMER0_OVF_vect) |
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{ |
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// copy these to local variables so they can be stored in registers
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// (volatile variables must be read from memory on every access)
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uint32_t m = timer0_millis; |
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uint8_t f = timer0_fract; |
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m += MILLIS_INC; |
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f += FRACT_INC; |
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if (f >= FRACT_MAX) { |
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f -= FRACT_MAX; |
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m += 1; |
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} |
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timer0_fract = f; |
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timer0_millis = m; |
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timer0_overflow_count++; |
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} |
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uint32_t AVRTimer::millis() |
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{ |
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uint32_t m; |
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uint8_t oldSREG = SREG; |
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// disable interrupts while we read timer0_millis or we might get an
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// inconsistent value (e.g. in the middle of a write to timer0_millis)
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cli(); |
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m = timer0_millis; |
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SREG = oldSREG; |
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return m; |
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} |
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uint32_t AVRTimer::micros() { |
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uint32_t m; |
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uint8_t t; |
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uint8_t oldSREG = SREG; |
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cli(); |
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m = timer0_overflow_count; |
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t = TCNT0; |
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if ((TIFR0 & _BV(TOV0)) && (t < 255)) |
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m++; |
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SREG = oldSREG; |
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return ((m << 8) + t) * (64 / clockCyclesPerMicrosecond()); |
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} |
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/* Delay for the given number of microseconds. Assumes a 16 MHz clock. */ |
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void AVRTimer::delay_microseconds(uint16_t us) |
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{ |
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// for the 16 MHz clock on most Arduino boards
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// for a one-microsecond delay, simply return. the overhead
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// of the function call yields a delay of approximately 1 1/8 us.
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if (--us == 0) |
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return; |
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// the following loop takes a quarter of a microsecond (4 cycles)
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// per iteration, so execute it four times for each microsecond of
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// delay requested.
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us <<= 2; |
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// account for the time taken in the preceeding commands.
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us -= 2; |
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// busy wait
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__asm__ __volatile__ ( |
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"1: sbiw %0,1" "\n\t" // 2 cycles
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"brne 1b" : "=w" (us) : "0" (us) // 2 cycles
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); |
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} |
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