timer_avr.c

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#include <drv/timer_avr.h>
#include <cfg/macros.h> // BV()

#include <cpu/types.h>
#include <cpu/irq.h>

#include <avr/interrupt.h>
#include <avr/io.h>

#if CPU_AVR_ATMEGA1281 || CPU_AVR_ATMEGA168
    #define REG_TIFR0 TIFR0
    #define REG_TIFR2 TIFR2

    #define REG_TIMSK0 TIMSK0
    #define REG_TIMSK2 TIMSK2

    #define REG_TCCR2A TCCR2A
    #define REG_TCCR2B TCCR2B

    #define REG_OCR2A  OCR2A

    #define BIT_OCF0A  OCF0A
    #define BIT_OCF2A  OCF2A

    #define BIT_OCIE0A OCIE0A
    #define BIT_OCIE2A OCIE2A
#else
    #define REG_TIFR0 TIFR
    #define REG_TIFR2 TIFR

    #define REG_TIMSK0 TIMSK
    #define REG_TIMSK2 TIMSK

    #define REG_TCCR2A TCCR2
    #define REG_TCCR2B TCCR2

    #define REG_OCR2A  OCR2

    #define BIT_OCF0A  OCF0
    #define BIT_OCF2A  OCF2

    #define BIT_OCIE0A OCIE0
    #define BIT_OCIE2A OCIE2
#endif


#if (CONFIG_TIMER == TIMER_ON_OUTPUT_COMPARE0)

    static void timer_hw_init(void)
    {
        cpuflags_t flags;
        IRQ_SAVE_DISABLE(flags);

        /* Reset Timer flags */
        REG_TIFR0 = BV(BIT_OCF0A) | BV(TOV0);

        /* Setup Timer/Counter interrupt */
        ASSR = 0x00;                  /* Internal system clock */
        TCCR0 = BV(WGM01)             /* Clear on Compare match */
            #if TIMER_PRESCALER == 64
                | BV(CS02)
            #else
                #error Unsupported value of TIMER_PRESCALER
            #endif
        ;
        TCNT0 = 0x00;                 /* Initialization of Timer/Counter */
        OCR0 = OCR_DIVISOR;           /* Timer/Counter Output Compare Register */

        /* Enable timer interrupts: Timer/Counter2 Output Compare (OCIE2) */
        REG_TIMSK0 &= ~BV(TOIE0);
        REG_TIMSK0 |= BV(OCIE0);

        IRQ_RESTORE(flags);
    }

    INLINE hptime_t timer_hw_hpread(void)
    {
        return TCNT0;
    }

#elif (CONFIG_TIMER == TIMER_ON_OVERFLOW1)

    static void timer_hw_init(void)
    {
        cpuflags_t flags;
        IRQ_SAVE_DISABLE(flags);

        /* Reset Timer overflow flag */
        TIFR |= BV(TOV1);

        /* Fast PWM mode, 9 bit, 24 kHz, no prescaling. */
        #if (TIMER_PRESCALER == 1) && (TIMER_HW_BITS == 9)
            TCCR1A |= BV(WGM11);
            TCCR1A &= ~BV(WGM10);
            TCCR1B |= BV(WGM12) | BV(CS10);
            TCCR1B &= ~(BV(WGM13) | BV(CS11) | BV(CS12));
        /* Fast PWM mode, 8 bit, 24 kHz, no prescaling. */
        #elif (TIMER_PRESCALER == 1) && (TIMER_HW_BITS == 8)
            TCCR1A |= BV(WGM10);
            TCCR1A &= ~BV(WGM11);
            TCCR1B |= BV(WGM12) | BV(CS10);
            TCCR1B &= ~(BV(WGM13) | BV(CS11) | BV(CS12));
        #else
            #error Unsupported value of TIMER_PRESCALER or TIMER_HW_BITS
        #endif

        TCNT1 = 0x00;         /* initialization of Timer/Counter */

        /* Enable timer interrupt: Timer/Counter1 Overflow */
        TIMSK |= BV(TOIE1);

        IRQ_RESTORE(flags);
    }

    INLINE hptime_t timer_hw_hpread(void)
    {
        return TCNT1;
    }

#elif (CONFIG_TIMER == TIMER_ON_OUTPUT_COMPARE2)
    static void timer_hw_init(void)
    {
        cpuflags_t flags;
        IRQ_SAVE_DISABLE(flags);

        /* Reset Timer flags */
        REG_TIFR2 = BV(BIT_OCF2A) | BV(TOV2);

        /* Setup Timer/Counter interrupt */
        REG_TCCR2A = 0; // TCCR2 reg could be separate or a unique register with both A & B values, this is needed to
        REG_TCCR2B = 0; // ensure correct initialization.

        REG_TCCR2A = BV(WGM21);
        #if TIMER_PRESCALER == 64
        #if CPU_AVR_ATMEGA1281 || CPU_AVR_ATMEGA168
            // ATMega1281 & ATMega168 have undocumented differences in timer2 prescaler!
            REG_TCCR2B |= BV(CS22);
        #else
            REG_TCCR2B |= BV(CS21) | BV(CS20);
        #endif
        #else
            #error Unsupported value of TIMER_PRESCALER
        #endif

        /* Clear on Compare match & prescaler = 64, internal sys clock.
           When changing prescaler change TIMER_HW_HPTICKS_PER_SEC too */
        TCNT2 = 0x00;         /* initialization of Timer/Counter */
        REG_OCR2A = OCR_DIVISOR;   /* Timer/Counter Output Compare Register */

        /* Enable timer interrupts: Timer/Counter2 Output Compare (OCIE2) */
        REG_TIMSK2 &= ~BV(TOIE2);
        REG_TIMSK2 |= BV(BIT_OCIE2A);

        IRQ_RESTORE(flags);
    }

    INLINE hptime_t timer_hw_hpread(void)
    {
        return TCNT2;
    }
#elif (CONFIG_TIMER == TIMER_ON_OVERFLOW3)

    static void timer_hw_init(void)
    {
        cpuflags_t flags;
        IRQ_SAVE_DISABLE(flags);

        /* Reset Timer overflow flag */
        TIFR |= BV(TOV3);

        /* Fast PWM mode, 9 bit, 24 kHz, no prescaling. */
        #if (TIMER_PRESCALER == 1) && (TIMER_HW_BITS == 9)
            TCCR3A |= BV(WGM31);
            TCCR3A &= ~BV(WGM30);
            TCCR3B |= BV(WGM32) | BV(CS30);
            TCCR3B &= ~(BV(WGM33) | BV(CS31) | BV(CS32));
        /* Fast PWM mode, 8 bit, 24 kHz, no prescaling. */
        #elif (TIMER_PRESCALER == 1) && (TIMER_HW_BITS == 8)
            TCCR3A |= BV(WGM30);
            TCCR3A &= ~BV(WGM31);
            TCCR3B |= BV(WGM32) | BV(CS30);
            TCCR3B &= ~(BV(WGM33) | BV(CS31) | BV(CS32));
        #else
            #error Unsupported value of TIMER_PRESCALER or TIMER_HW_BITS
        #endif

        TCNT3 = 0x00;         /* initialization of Timer/Counter */

        /* Enable timer interrupt: Timer/Counter3 Overflow */
        /* ATTENTION! TOIE3 is only on ETIMSK, not TIMSK */
        ETIMSK |= BV(TOIE3);

        IRQ_RESTORE(flags);
    }

    INLINE hptime_t timer_hw_hpread(void)
    {
        return TCNT3;
    }

#else
    #error Unimplemented value for CONFIG_TIMER
#endif /* CONFIG_TIMER */