ti-driverlib/driverlib/systick.c

//*****************************************************************************
//
// systick.c - Driver for the SysTick timer in NVIC.
//
// Copyright (c) 2005-2012 Texas Instruments Incorporated.  All rights reserved.
// Software License Agreement
//
//   Redistribution and use in source and binary forms, with or without
//   modification, are permitted provided that the following conditions
//   are met:
//
//   Redistributions of source code must retain the above copyright
//   notice, this list of conditions and the following disclaimer.
//
//   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.
//
//   Neither the name of Texas Instruments Incorporated 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
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// This is part of revision 9453 of the Stellaris Peripheral Driver Library.
//
//*****************************************************************************

//*****************************************************************************
//
//! \addtogroup systick_api
//! @{
//
//*****************************************************************************

#include "inc/hw_ints.h"
#include "inc/hw_nvic.h"
#include "inc/hw_types.h"
#include "driverlib/debug.h"
#include "driverlib/interrupt.h"
#include "driverlib/systick.h"

//*****************************************************************************
//
//! Enables the SysTick counter.
//!
//! This function starts the SysTick counter.  If an interrupt handler has been
//! registered, it is called when the SysTick counter rolls over.
//!
//! \note Calling this function causes the SysTick counter to (re)commence
//! counting from its current value.  The counter is not automatically reloaded
//! with the period as specified in a previous call to SysTickPeriodSet().  If
//! an immediate reload is required, the \b NVIC_ST_CURRENT register must be
//! written to force the reload.  Any write to this register clears the SysTick
//! counter to 0 and causes a reload with the supplied period on the next
//! clock.
//!
//! \return None.
//
//*****************************************************************************
void
SysTickEnable(void)
{
    //
    // Enable SysTick.
    //
    HWREG(NVIC_ST_CTRL) |= NVIC_ST_CTRL_CLK_SRC | NVIC_ST_CTRL_ENABLE;
}

//*****************************************************************************
//
//! Disables the SysTick counter.
//!
//! This function stops the SysTick counter.  If an interrupt handler has been
//! registered, it is not called until SysTick is restarted.
//!
//! \return None.
//
//*****************************************************************************
void
SysTickDisable(void)
{
    //
    // Disable SysTick.
    //
    HWREG(NVIC_ST_CTRL) &= ~(NVIC_ST_CTRL_ENABLE);
}

//*****************************************************************************
//
//! Registers an interrupt handler for the SysTick interrupt.
//!
//! \param pfnHandler is a pointer to the function to be called when the
//! SysTick interrupt occurs.
//!
//! This function registers the handler to be called when a SysTick interrupt
//! occurs.
//!
//! \sa IntRegister() for important information about registering interrupt
//! handlers.
//!
//! \return None.
//
//*****************************************************************************
void
SysTickIntRegister(void (*pfnHandler)(void))
{
    //
    // Register the interrupt handler, returning an error if an error occurs.
    //
    IntRegister(FAULT_SYSTICK, pfnHandler);

    //
    // Enable the SysTick interrupt.
    //
    HWREG(NVIC_ST_CTRL) |= NVIC_ST_CTRL_INTEN;
}

//*****************************************************************************
//
//! Unregisters the interrupt handler for the SysTick interrupt.
//!
//! This function unregisters the handler to be called when a SysTick interrupt
//! occurs.
//!
//! \sa IntRegister() for important information about registering interrupt
//! handlers.
//!
//! \return None.
//
//*****************************************************************************
void
SysTickIntUnregister(void)
{
    //
    // Disable the SysTick interrupt.
    //
    HWREG(NVIC_ST_CTRL) &= ~(NVIC_ST_CTRL_INTEN);

    //
    // Unregister the interrupt handler.
    //
    IntUnregister(FAULT_SYSTICK);
}

//*****************************************************************************
//
//! Enables the SysTick interrupt.
//!
//! This function enables the SysTick interrupt, allowing it to be
//! reflected to the processor.
//!
//! \note The SysTick interrupt handler is not required to clear the SysTick
//! interrupt source because it is cleared automatically by the NVIC when the
//! interrupt handler is called.
//!
//! \return None.
//
//*****************************************************************************
void
SysTickIntEnable(void)
{
    //
    // Enable the SysTick interrupt.
    //
    HWREG(NVIC_ST_CTRL) |= NVIC_ST_CTRL_INTEN;
}

//*****************************************************************************
//
//! Disables the SysTick interrupt.
//!
//! This function disables the SysTick interrupt, preventing it from being
//! reflected to the processor.
//!
//! \return None.
//
//*****************************************************************************
void
SysTickIntDisable(void)
{
    //
    // Disable the SysTick interrupt.
    //
    HWREG(NVIC_ST_CTRL) &= ~(NVIC_ST_CTRL_INTEN);
}

//*****************************************************************************
//
//! Sets the period of the SysTick counter.
//!
//! \param ulPeriod is the number of clock ticks in each period of the SysTick
//! counter and must be between 1 and 16,777,216, inclusive.
//!
//! This function sets the rate at which the SysTick counter wraps, which
//! equates to the number of processor clocks between interrupts.
//!
//! \note Calling this function does not cause the SysTick counter to reload
//! immediately.  If an immediate reload is required, the \b NVIC_ST_CURRENT
//! register must be written.  Any write to this register clears the SysTick
//! counter to 0 and causes a reload with the \e ulPeriod supplied here on
//! the next clock after SysTick is enabled.
//!
//! \return None.
//
//*****************************************************************************
void
SysTickPeriodSet(unsigned long ulPeriod)
{
    //
    // Check the arguments.
    //
    ASSERT((ulPeriod > 0) && (ulPeriod <= 16777216));

    //
    // Set the period of the SysTick counter.
    //
    HWREG(NVIC_ST_RELOAD) = ulPeriod - 1;
}

//*****************************************************************************
//
//! Gets the period of the SysTick counter.
//!
//! This function returns the rate at which the SysTick counter wraps, which
//! equates to the number of processor clocks between interrupts.
//!
//! \return Returns the period of the SysTick counter.
//
//*****************************************************************************
unsigned long
SysTickPeriodGet(void)
{
    //
    // Return the period of the SysTick counter.
    //
    return(HWREG(NVIC_ST_RELOAD) + 1);
}

//*****************************************************************************
//
//! Gets the current value of the SysTick counter.
//!
//! This function returns the current value of the SysTick counter, which is
//! a value between the period - 1 and zero, inclusive.
//!
//! \return Returns the current value of the SysTick counter.
//
//*****************************************************************************
unsigned long
SysTickValueGet(void)
{
    //
    // Return the current value of the SysTick counter.
    //
    return(HWREG(NVIC_ST_CURRENT));
}

//*****************************************************************************
//
// Close the Doxygen group.
//! @}
//
//*****************************************************************************