drivers/timer/altera_avalon_timer.c

/*
 * Copyright (c) 2016 Intel Corporation
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <kernel.h>
#include <arch/cpu.h>
#include <device.h>
#include <system_timer.h>

/* STATUS register */
#define ALTERA_AVALON_TIMER_STATUS_REG              0
#define ALTERA_AVALON_TIMER_STATUS_TO_MSK           (0x1)
#define ALTERA_AVALON_TIMER_STATUS_TO_OFST          (0)
#define ALTERA_AVALON_TIMER_STATUS_RUN_MSK          (0x2)
#define ALTERA_AVALON_TIMER_STATUS_RUN_OFST         (1)

/* CONTROL register */
#define ALTERA_AVALON_TIMER_CONTROL_REG             1
#define ALTERA_AVALON_TIMER_CONTROL_ITO_MSK         (0x1)
#define ALTERA_AVALON_TIMER_CONTROL_ITO_OFST        (0)
#define ALTERA_AVALON_TIMER_CONTROL_CONT_MSK        (0x2)
#define ALTERA_AVALON_TIMER_CONTROL_CONT_OFST       (1)
#define ALTERA_AVALON_TIMER_CONTROL_START_MSK       (0x4)
#define ALTERA_AVALON_TIMER_CONTROL_START_OFST      (2)
#define ALTERA_AVALON_TIMER_CONTROL_STOP_MSK        (0x8)
#define ALTERA_AVALON_TIMER_CONTROL_STOP_OFST       (3)

/* Period and SnapShot Register for COUNTER_SIZE = 32 */
/*----------------------------------------------------*/
/* PERIODL register */
#define ALTERA_AVALON_TIMER_PERIODL_REG             2
#define ALTERA_AVALON_TIMER_PERIODL_MSK             (0xFFFF)
#define ALTERA_AVALON_TIMER_PERIODL_OFST            (0)

/* PERIODH register */
#define ALTERA_AVALON_TIMER_PERIODH_REG             3
#define ALTERA_AVALON_TIMER_PERIODH_MSK             (0xFFFF)
#define ALTERA_AVALON_TIMER_PERIODH_OFST            (0)

/* SNAPL register */
#define ALTERA_AVALON_TIMER_SNAPL_REG               4
#define ALTERA_AVALON_TIMER_SNAPL_MSK               (0xFFFF)
#define ALTERA_AVALON_TIMER_SNAPL_OFST              (0)

/* SNAPH register */
#define ALTERA_AVALON_TIMER_SNAPH_REG               5
#define ALTERA_AVALON_TIMER_SNAPH_MSK               (0xFFFF)
#define ALTERA_AVALON_TIMER_SNAPH_OFST              (0)

static u32_t accumulated_cycle_count;

static void timer_irq_handler(void *unused)
{
	ARG_UNUSED(unused);

	/* Clear the interrupt */
	_nios2_reg_write((void *)TIMER_0_BASE, ALTERA_AVALON_TIMER_STATUS_REG,
			 0);
	accumulated_cycle_count += sys_clock_hw_cycles_per_tick;

	_sys_clock_tick_announce();
}


#ifdef CONFIG_TICKLESS_IDLE
#error "Tickless idle not yet implemented for Avalon timer"
#endif


int _sys_clock_driver_init(struct device *device)
{
	ARG_UNUSED(device);

#if TIMER_0_FIXED_PERIOD
#error "Can't set timer period!"
#else
	_nios2_reg_write((void *)TIMER_0_BASE, ALTERA_AVALON_TIMER_PERIODL_REG,
			 sys_clock_hw_cycles_per_tick & 0xFFFF);
	_nios2_reg_write((void *)TIMER_0_BASE, ALTERA_AVALON_TIMER_PERIODH_REG,
			 (sys_clock_hw_cycles_per_tick >> 16) & 0xFFFF);
#endif

	IRQ_CONNECT(TIMER_0_IRQ, 0, timer_irq_handler, NULL, 0);
	irq_enable(TIMER_0_IRQ);

	/* Initial configuration: Generate interrupts, run continuously,
	 * start running
	 */
	_nios2_reg_write((void *)TIMER_0_BASE, ALTERA_AVALON_TIMER_CONTROL_REG,
			 ALTERA_AVALON_TIMER_CONTROL_ITO_MSK  |
			 ALTERA_AVALON_TIMER_CONTROL_CONT_MSK |
			 ALTERA_AVALON_TIMER_CONTROL_START_MSK);
	return 0;
}


u32_t _timer_cycle_get_32(void)
{
	/* XXX Per the Altera Embedded IP Peripherals guide, you cannot
	 * use a timer instance for both the system clock and timestamps
	 * at the same time.
	 *
	 * Having this function return accumulated_cycle_count + get_snapshot()
	 * does not work reliably. It's possible for the current countdown
	 * to reset to the next interval before the timer interrupt is
	 * delivered (and accumulated cycle count gets updated). The result
	 * is an unlucky call to this function will appear to jump backward
	 * in time.
	 *
	 * To properly obtain timestamps, the CPU must be configured with
	 * a second timer peripheral instance that is configured to
	 * count down from some large initial 64-bit value. This
	 * is currently unimplemented.
	 */
	return accumulated_cycle_count;
}