/****************************************************************************
* arch/avr/src/atmega/atmega_timerisr.c
*
* Copyright (C) 2011 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name NuttX nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <stdint.h>
#include <time.h>
#include <debug.h>
#include <nuttx/arch.h>
#include <arch/board/board.h>
#include <avr/io.h>
#include "up_arch.h"
#include "atmega_internal.h"
/****************************************************************************
* Definitions
****************************************************************************/
/* The CPU frequency is given by BOARD_CPU_CLOCK (defined in board.h). The
* desired interrupt frequency is given by CONFIG_MSEC_PER_TICK. An unscaled
* ideal match is given by:
*
* CLOCK = CPU_CLOCK / DIVISOR # CPU clocks/sec
* MATCH = CLOCK / CLOCKS_PER_SEC # CPU clocks/timer tick
* MATCH = CPU_CLOCK / DIVISOR / CLOCKS_PER_SEC # CPU clocks/timer tick
*
* But we only have 16-bits of accuracy so we need to pick the smallest
* divisor using the following brute force calculation:
*/
#define MATCH1 (( BOARD_CPU_CLOCK + CLOCKS_PER_SEC/2) / CLOCKS_PER_SEC)
#define MATCH8 ((((BOARD_CPU_CLOCK + 4) / 8) + CLOCKS_PER_SEC/2) / CLOCKS_PER_SEC)
#define MATCH64 ((((BOARD_CPU_CLOCK + 8) / 64) + CLOCKS_PER_SEC/2) / CLOCKS_PER_SEC)
#define MATCH256 ((((BOARD_CPU_CLOCK + 128) / 256) + CLOCKS_PER_SEC/2) / CLOCKS_PER_SEC)
#define MATCH1024 ((((BOARD_CPU_CLOCK + 512) / 1024) + CLOCKS_PER_SEC/2) / CLOCKS_PER_SEC)
#if MATCH1 <= 65536
# define MATCH (MATCH1-1)
# define PRESCALE 1
#elif MATCH8 <= 65536
# define MATCH (MATCH8-1)
# define PRESCALE 2
#elif MATCH64 <= 65536
# define MATCH (MATCH64-1)
# define PRESCALE 3
#elif MATCH256 <= 65536
# define MATCH (MATCH256-1)
# define PRESCALE 4
#elif MATCH1024 <= 65536
# define MATCH (MATCH1024-1)
# define PRESCALE 5
#else
# error "Cannot represent this timer frequency"
#endif
/*
* Eg. CPU_CLOCK = 8MHz, CLOCKS_PER_SEC = 100
*
* MATCH1 ((8000000 + 50) / 100) = 80,000 FREQ=100.0Hz
* MATCH8 ((1000000 + 50) / 100) = 10,000 FREQ=100.0Hz <-- this one
* MATCH64 (( 125000 + 50) / 100) = 1,250 FREQ=100.0Hz
* MATCH256 (( 31250 + 50) / 100) = 313 FREQ=99.8Hz
* MATCH1024 (( 7804 + 50) / 100) = 78 FREQ=100.1Hz
*/
/****************************************************************************
* Private Types
****************************************************************************/
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Global Functions
****************************************************************************/
/****************************************************************************
* Function: up_timerisr
*
* Description:
* The timer ISR will perform a variety of services for various portions
* of the systems.
*
****************************************************************************/
int up_timerisr(int irq, uint32_t *regs)
{
/* Process timer interrupt */
sched_process_timer();
return 0;
}
/****************************************************************************
* Function: up_timerinit
*
* Description:
* This function is called during start-up to initialize the timer
* interrupt. NOTE: This function depends on setup of OSC32 by
* up_clkinitialize().
*
****************************************************************************/
void up_timerinit(void)
{
/* Setup timer 1 compare match A to generate a tick interrupt.
*
* First, setup the match value for compare match A.
*/
OCR1AH = (uint8_t)((uint16_t)MATCH >> 8);
OCR1AL = (uint8_t)((uint16_t)MATCH & 0xff);
/* Setup clock source and compare match behaviour. */
TCCR1A = 0x08 | PRESCALE;
/* Attach the timer interrupt vector */
(void)irq_attach(AT90USB_IRQ_T2COMPA, (xcpt_t)up_timerisr);
/* Enable the interrupt on compare match A */
TIMSK1 |= 0x10;
}
