/*
* arch/v850/kernel/highres_timer.c -- High resolution timing routines
*
* Copyright (C) 2001,02,03 NEC Electronics Corporation
* Copyright (C) 2001,02,03 Miles Bader <miles@gnu.org>
*
* This file is subject to the terms and conditions of the GNU General
* Public License. See the file COPYING in the main directory of this
* archive for more details.
*
* Written by Miles Bader <miles@gnu.org>
*/
#include <asm/system.h>
#include <asm/v850e_timer_d.h>
#include <asm/highres_timer.h>
#define HIGHRES_TIMER_USEC_SHIFT 12
/* Pre-calculated constant used for converting ticks to real time
units. We initialize it to prevent it being put into BSS. */
static u32 highres_timer_usec_prescale = 1;
void highres_timer_slow_tick_irq (void) __attribute__ ((noreturn));
void highres_timer_slow_tick_irq (void)
{
/* This is an interrupt handler, so it must be very careful to
not to trash any registers. At this point, the stack-pointer
(r3) has been saved in the chip ram location ENTRY_SP by the
interrupt vector, so we can use it as a scratch register; we
must also restore it before returning. */
asm ("ld.w %0[r0], sp;"
"add 1, sp;"
"st.w sp, %0[r0];"
"ld.w %1[r0], sp;" /* restore pre-irq stack-pointer */
"reti"
::
"i" (HIGHRES_TIMER_SLOW_TICKS_ADDR),
"i" (ENTRY_SP_ADDR)
: "memory");
}
void highres_timer_reset (void)
{
V850E_TIMER_D_TMD (HIGHRES_TIMER_TIMER_D_UNIT) = 0;
HIGHRES_TIMER_SLOW_TICKS = 0;
}
void highres_timer_start (void)
{
u32 fast_tick_rate;
/* Start hardware timer. */
v850e_timer_d_configure (HIGHRES_TIMER_TIMER_D_UNIT,
HIGHRES_TIMER_SLOW_TICK_RATE);
fast_tick_rate =
(V850E_TIMER_D_BASE_FREQ
>> V850E_TIMER_D_DIVLOG2 (HIGHRES_TIMER_TIMER_D_UNIT));
/* The obvious way of calculating microseconds from fast ticks
is to do:
usec = fast_ticks * 10^6 / fast_tick_rate
However, divisions are much slower than multiplications, and
the above calculation can overflow, so we do this instead:
usec = fast_ticks * (10^6 * 2^12 / fast_tick_rate) / 2^12
since we can pre-calculate (10^6 * (2^12 / fast_tick_rate))
and use a shift for dividing by 2^12, this avoids division,
and is almost as accurate (it differs by about 2 microseconds
at the extreme value of the fast-tick counter's ranger). */
highres_timer_usec_prescale = ((1000000 << HIGHRES_TIMER_USEC_SHIFT)
/ fast_tick_rate);
/* Enable the interrupt (which is hardwired to this use), and
give it the highest priority. */
V850E_INTC_IC (IRQ_INTCMD (HIGHRES_TIMER_TIMER_D_UNIT)) = 0;
}
void highres_timer_stop (void)
{
/* Stop the timer. */
V850E_TIMER_D_TMCD (HIGHRES_TIMER_TIMER_D_UNIT) =
V850E_TIMER_D_TMCD_CAE;
/* Disable its interrupt, just in case. */
v850e_intc_disable_irq (IRQ_INTCMD (HIGHRES_TIMER_TIMER_D_UNIT));
}
inline void highres_timer_read_ticks (u32 *slow_ticks, u32 *fast_ticks)
{
int flags;
u32 fast_ticks_1, fast_ticks_2, _slow_ticks;
local_irq_save (flags);
fast_ticks_1 = V850E_TIMER_D_TMD (HIGHRES_TIMER_TIMER_D_UNIT);
_slow_ticks = HIGHRES_TIMER_SLOW_TICKS;
fast_ticks_2 = V850E_TIMER_D_TMD (HIGHRES_TIMER_TIMER_D_UNIT);
local_irq_restore (flags);
if (fast_ticks_2 < fast_ticks_1)
_slow_ticks++;
*slow_ticks = _slow_ticks;
*fast_ticks = fast_ticks_2;
}
inline void highres_timer_ticks_to_timeval (u32 slow_ticks, u32 fast_ticks,
struct timeval *tv)
{
unsigned long sec, sec_rem, usec;
usec = ((fast_ticks * highres_timer_usec_prescale)
>> HIGHRES_TIMER_USEC_SHIFT);
sec = slow_ticks / HIGHRES_TIMER_SLOW_TICK_RATE;
sec_rem = slow_ticks % HIGHRES_TIMER_SLOW_TICK_RATE;
usec += sec_rem * (1000000 / HIGHRES_TIMER_SLOW_TICK_RATE);
tv->tv_sec = sec;
tv->tv_usec = usec;
}
void highres_timer_read (struct timeval *tv)
{
u32 fast_ticks, slow_ticks;
highres_timer_read_ticks (&slow_ticks, &fast_ticks);
highres_timer_ticks_to_timeval (slow_ticks, fast_ticks, tv);
}
