source: rtems/c/src/lib/libcpu/powerpc/ppc403/clock/clock.c @ 5072b07

/*  clock.c
 *
 *  This routine initializes the interval timer on the
 *  PowerPC 403 CPU.  The tick frequency is specified by the bsp.
 *
 *  Author:     Andrew Bray <andy@i-cubed.demon.co.uk>
 *
 *  COPYRIGHT (c) 1995 by i-cubed ltd.
 *
 *  To anyone who acknowledges that this file is provided "AS IS"
 *  without any express or implied warranty:
 *      permission to use, copy, modify, and distribute this file
 *      for any purpose is hereby granted without fee, provided that
 *      the above copyright notice and this notice appears in all
 *      copies, and that the name of i-cubed limited not be used in
 *      advertising or publicity pertaining to distribution of the
 *      software without specific, written prior permission.
 *      i-cubed limited makes no representations about the suitability
 *      of this software for any purpose.
 *
 *  Derived from c/src/lib/libcpu/hppa1_1/clock/clock.c:
 *
 *  COPYRIGHT (c) 1989, 1990, 1991, 1992, 1993, 1994.
 *  On-Line Applications Research Corporation (OAR).
 *  All rights assigned to U.S. Government, 1994.
 *
 *  This material may be reproduced by or for the U.S. Government pursuant
 *  to the copyright license under the clause at DFARS 252.227-7013.  This
 *  notice must appear in all copies of this file and its derivatives.
 *
 *  clock.c,v 1.2 1995/05/31 16:59:06 joel Exp
 */

#include <bsp.h>
#include <clockdrv.h>

#include <stdlib.h>                     /* for atexit() */

extern rtems_cpu_table           Cpu_table;             /* owned by BSP */

volatile rtems_unsigned32 Clock_driver_ticks;
static rtems_unsigned32 pit_value, tick_time;
static rtems_boolean auto_restart;

rtems_device_driver Clock_initialize(
  rtems_device_major_number major,
  rtems_device_minor_number minor,
  void *pargp,
  rtems_id tid,
  rtems_unsigned32 *rval
)
{
    Install_clock(Clock_isr);
}


void
ReInstall_clock(rtems_isr_entry new_clock_isr)
{
    rtems_isr_entry previous_isr;
    rtems_unsigned32 isrlevel = 0;

    rtems_interrupt_disable(isrlevel);
    
    rtems_interrupt_catch(new_clock_isr, PPC_IRQ_PIT,
                          &previous_isr);

    rtems_interrupt_enable(isrlevel);
}

static INLINE rtems_unsigned32 get_itimer(void)
{
    register rtems_unsigned32 rc;

    asm volatile ("mftblo %0" : "=r" ((rc)));

    return rc;
}

void Install_clock(rtems_isr_entry clock_isr)
{
    rtems_isr_entry previous_isr;
    rtems_unsigned32 pvr, iocr;

    Clock_driver_ticks = 0;

    asm volatile ("mfiocr %0" : "=r" (iocr));
    iocr &= ~4;
    iocr |= 4;  /* Select external timer clock */
    asm volatile ("mtiocr %0" : "=r" (iocr) : "0" (iocr));

    asm volatile ("mfpvr %0" : "=r" ((pvr)));

    if (((pvr & 0xffff0000) >> 16) != 0x0020)
        return; /* Not a ppc403 */

    if ((pvr & 0xff00) == 0x0000) /* 403GA */
        auto_restart = (pvr & 0x00f0) > 0x0000 ? 1 : 0;
    else if ((pvr & 0xff00) == 0x0100) /* 403GB */
        auto_restart = 1;

    pit_value = BSP_Configuration.microseconds_per_tick *
        Cpu_table.clicks_per_usec;

    if (BSP_Configuration.ticks_per_timeslice)
    {
        register rtems_unsigned32 tcr;
        /*
         * initialize the interval here
         * First tick is set to right amount of time in the future
         * Future ticks will be incremented over last value set
         * in order to provide consistent clicks in the face of
         * interrupt overhead
         */

        rtems_interrupt_catch(clock_isr, PPC_IRQ_PIT,
                              &previous_isr);

        asm volatile ("mtpit %0" : : "r" (pit_value));

        asm volatile ("mftcr %0" : "=r" ((tcr)));

        tcr &= ~ 0x04400000;

        tcr |= (auto_restart ? 0x04400000 : 0x04000000);

        tick_time = get_itimer() + pit_value;

        asm volatile ("mttcr %0" : "=r" ((tcr)) : "0" ((tcr)));
    }
    atexit(Clock_exit);
}


rtems_isr
Clock_isr(rtems_vector_number vector)
{
    if (!auto_restart)
        {
            rtems_unsigned32 clicks_til_next_interrupt;
            rtems_unsigned32 itimer_value;

            /*
             * setup for next interrupt; making sure the new value is reasonably
             * in the future.... in case we lost out on an interrupt somehow
             */

            itimer_value = get_itimer();
            tick_time += pit_value;

            /*
             * how far away is next interrupt *really*
             * It may be a long time; this subtraction works even if
             * Clock_clicks_interrupt < Clock_clicks_low_order via
             * the miracle of unsigned math.
             */
            clicks_til_next_interrupt = tick_time - itimer_value;

            /*
             * If it is too soon then bump it up.
             * This should only happen if CPU_HPPA_CLICKS_PER_TICK is too small.
             * But setting it low is useful for debug, so...
             */

            if (clicks_til_next_interrupt < 400)
                {
                    tick_time = itimer_value + 1000;
                    clicks_til_next_interrupt = 1000;
                    /* XXX: count these! this should be rare */
                }

            /*
             * If it is too late, that means we missed the interrupt somehow.
             * Rather than wait 35-50s for a wrap, we just fudge it here.
             */
            
            if (clicks_til_next_interrupt > pit_value)
                {
                    tick_time = itimer_value + 1000;
                    clicks_til_next_interrupt = 1000;
                    /* XXX: count these! this should never happen :-) */
                }

            asm volatile ("mtpit %0" :: "r" (clicks_til_next_interrupt));
        }

    asm volatile ( "mttsr %0" :: "r" (0x08000000));

    Clock_driver_ticks++;

    rtems_clock_tick();
}

/*
 * Called via atexit()
 * Remove the clock interrupt handler by setting handler to NULL
 */

void
Clock_exit(void)
{
    if ( BSP_Configuration.ticks_per_timeslice )
    {
        register rtems_unsigned32 tcr;

        asm volatile ("mftcr %0" : "=r" ((tcr)));

        tcr &= ~ 0x04400000;

        asm volatile ("mttcr %0" : "=r" ((tcr)) : "0" ((tcr)));

        (void) set_vector(0, PPC_IRQ_PIT, 1);
    }
}