drivers/delay_timer/generic_delay_timer.c

/*
 * Copyright (c) 2016, ARM Limited and Contributors. All rights reserved.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include <arch_helpers.h>
#include <assert.h>
#include <bl_common.h>
#include <debug.h>
#include <delay_timer.h>
#include <platform.h>

/* Ticks elapsed in one second by a signal of 1 MHz */
#define MHZ_TICKS_PER_SEC 1000000

static timer_ops_t ops;

static uint32_t get_timer_value(void)
{
	/*
	 * Generic delay timer implementation expects the timer to be a down
	 * counter. We apply bitwise NOT operator to the tick values returned
	 * by read_cntpct_el0() to simulate the down counter. The value is
	 * clipped from 64 to 32 bits.
	 */
	return (uint32_t)(~read_cntpct_el0());
}

void generic_delay_timer_init_args(uint32_t mult, uint32_t div)
{
	ops.get_timer_value	= get_timer_value;
	ops.clk_mult		= mult;
	ops.clk_div		= div;

	timer_init(&ops);

	VERBOSE("Generic delay timer configured with mult=%u and div=%u\n",
		mult, div);
}

void generic_delay_timer_init(void)
{
	/* Value in ticks */
	unsigned int mult = MHZ_TICKS_PER_SEC;

	/* Value in ticks per second (Hz) */
	unsigned int div  = plat_get_syscnt_freq2();

	/* Reduce multiplier and divider by dividing them repeatedly by 10 */
	while ((mult % 10 == 0) && (div % 10 == 0)) {
		mult /= 10;
		div /= 10;
	}

	generic_delay_timer_init_args(mult, div);
}