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/*
* This routine initializes the MC68360 Periodic Interval Timer
*
* The PIT has rather poor resolution, but it is easy to set up
* and requires no housekeeping once it is going.
*
* W. Eric Norum
* Saskatchewan Accelerator Laboratory
* University of Saskatchewan
* Saskatoon, Saskatchewan, CANADA
* eric@skatter.usask.ca
*/
#include <rtems.h>
#include <bsp.h>
#include <rtems/m68k/m68360.h>
#define CLOCK_VECTOR 120
#define CLOCK_IRQ_LEVEL 4
char M360DefaultWatchdogFeeder = 1;
/*
* RTEMS and hardware have different notions of clock rate.
*/
static unsigned long rtems_nsec_per_tick;
static unsigned long pit_nsec_per_tick;
static unsigned long nsec;
/*
* Periodic interval timer interrupt handler
* See if it's really time for a `tick'
* Perform a dummy read of DPRAM (work around bug in Rev. B of the 68360).
* Feed the watchdog
* Application code can override this by
* setting M360DefaultWatchdogFeeder to zero.
*/
#define Clock_driver_support_at_tick() \
do { \
nsec += pit_nsec_per_tick; \
if (nsec >= rtems_nsec_per_tick) \
return; \
nsec -= rtems_nsec_per_tick; \
m360.dpram0[0]; \
if (M360DefaultWatchdogFeeder) { \
m360.swsr = 0x55; \
m360.swsr = 0xAA; \
} \
} while (0) \
/*
* Attach clock interrupt handler
*/
#define Clock_driver_support_install_isr( _new ) \
set_vector(_new, CLOCK_VECTOR, 1)
/*
* Turn off the clock
*/
#define Clock_driver_support_shutdown_hardware() \
do { \
m360.pitr &= ~0xFF; \
} while(0)
/*
* Set up the clock hardware
* The rate at which the periodic interval timer
* can generate interrupts is almost certainly not
* the same as desired by the BSP configuration.
* Handle the difference by choosing the largest PIT
* interval which is less than or equal to the RTEMS
* interval and skipping some hardware interrupts.
* To reduce the jitter in the calls to RTEMS the
* hardware interrupt interval is never greater than
* the maximum non-prescaled value from the PIT.
*
* For a 25 MHz external clock the basic clock rate is
* 40 nsec * 128 * 4 = 20.48 usec/tick
*/
extern int m360_clock_rate;
#define Clock_driver_support_initialize_hardware() \
do { \
unsigned int divisor; \
unsigned long nsec_per_chip_tick = 1000000000 / m360_clock_rate; \
unsigned long nsec_per_pit_tick = 512 * nsec_per_chip_tick; \
rtems_nsec_per_tick = rtems_configuration_get_microseconds_per_tick() * 1000; \
divisor = rtems_nsec_per_tick / nsec_per_pit_tick; \
if (divisor > 255) \
divisor = 255; \
else if (divisor == 0) \
divisor = 1; \
pit_nsec_per_tick = nsec_per_pit_tick * divisor; \
m360.pitr &= ~0x1FF; \
m360.picr = (CLOCK_IRQ_LEVEL << 8) | CLOCK_VECTOR; \
m360.pitr |= divisor; \
} while (0)
#define CLOCK_DRIVER_USE_DUMMY_TIMECOUNTER
#include "../../../shared/clockdrv_shell.h"
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