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/**
* @file timer.c
*
* GBA Timer driver.
*/
/*
* RTEMS GBA BSP
*
* Copyright (c) 2002 by Jay Monkman <jtm@smoothsmoothie.com>
*
* Copyright (c) 2004 Markku Puro <markku.puro@kopteri.net>
*
* The license and distribution terms for this file may be
* found in found in the file LICENSE in this distribution or at
* http://www.rtems.com/license/LICENSE.
*
*
* Notes:
* This file manages the benchmark timer used by the RTEMS Timing Test
* Suite. Each measured time period is demarcated by calls to
* Timer_initialize() and Read_timer(). Read_timer() usually returns
* the number of microseconds since Timer_initialize() exitted.
*
* It is important that the timer start/stop overhead be determined
* when porting or modifying this code.
*
* $Id$
*/
#include <rtems.h>
#include <bsp.h>
#include <irq.h>
#include <gba.h>
/*
* Set up the timer hardware
* 1 / 16.78Mhz => 59.595 ns
* 64 / 16.78Mhz => 3.814 us
* 256 / 16.78Mhz => 15.256 us
* 1024 / 16.78Mhz => 61.025 us
*/
#define __TimePreScaler 1
#define __TickTime_ns ((1000000000L/__ClockFrequency)*__TimePreScaler)
#define __TickTime_us ((1000000L/__ClockFrequency)*__TimePreScaler)
#if (__TimePreScaler==1)
#define GBA_TM0CNT_PS 0x0000
#elif (__TimePreScaler==64)
#define GBA_TM0CNT_PS 0x0001
#elif (__TimePreScaler==256)
#define GBA_TM0CNT_PS 0x0002
#elif (__TimePreScaler==1024)
#define GBA_TM0CNT_PS 0x0003
#else
#define GBA_TM0CNT_PS 0x0003
#endif
rtems_boolean Timer_driver_Find_average_overhead;
/**
* @brief Timer_initialize start TM0 and TM1
*
* @param None
* @return None
*/
void Timer_initialize( void )
{
GBA_REG_TM1CNT = 0x0000; /* Stop Counters */
GBA_REG_TM0CNT = 0x0000;
GBA_REG_TM1D = 0x0000; /* Reset Counters */
GBA_REG_TM0D = 0x0000;
/* Start Counters */
GBA_REG_TM1CNT = 0x0084; /* Start Count Up timing */
GBA_REG_TM0CNT = (0x0080|GBA_TM0CNT_PS); /* Start Count */
}
/*
* The following controls the behavior of Read_timer().
*
* AVG_OVEREHAD is the overhead for starting and stopping the timer. It
* is usually deducted from the number returned.
*
* LEAST_VALID is the lowest number this routine should trust. Numbers
* below this are "noise" and zero is returned.
*/
#define AVG_OVERHEAD 3 /**< It typically takes 3 microseconds */
#define LEAST_VALID 1 /**< Don't trust a clicks value lower than this */
/**
* @brief Read_timer return timer countervalue in microseconds.
*
* Used in Timing Test Suite.
*
* @param None
* @return Timer value in microseconds
*/
uint32_t Read_timer( void )
{
uint32_t ticks;
uint32_t total;
/* Stop Counters */
GBA_REG_TM0CNT = 0x0000;
GBA_REG_TM1CNT = 0x0000;
/* Read Counters */
ticks = (GBA_REG_TM1D<<16) | GBA_REG_TM0D;
if ( ticks < LEAST_VALID ) {
return 0; /* below timer resolution */
}
/* convert to uS */
total = ((ticks * __TickTime_ns) / 1000);
if ( Timer_driver_Find_average_overhead == 1 ) {
return total; /* in microseconds */
}
else {
if ( total < AVG_OVERHEAD ) {
return 0;
}
return (total - AVG_OVERHEAD);
}
}
/**
* @brief Empty function
*
* Empty function call used in loops to measure basic cost of looping
* in Timing Test Suite.
*
* @param None
* @return RTEMS_SUCCESSFUL
*/
rtems_status_code Empty_function( void )
{
return RTEMS_SUCCESSFUL;
}
/**
* @brief Set Timer_driver_Find_average_overhead flag.
*
* Used in Timing Test Suite.
*
* @param find_flag boolean find_flag
* @return None
*/
void Set_find_average_overhead(rtems_boolean find_flag)
{
Timer_driver_Find_average_overhead = find_flag;
}
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