Tick.c

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// ////////////////////////////////////////////////////////////////////////////
// ////////////////////////////////////////////////////////////////////////////
/*********************************************************************
 * Software License Agreement
 *
 * Copyright (C) 2002-2008 Microchip Technology Inc.  All rights 
 * reserved.
 *
 * Microchip licenses to you the right to use, modify, copy, and 
 * distribute: 
 * (i)  the Software when embedded on a Microchip microcontroller or 
 *      digital signal controller product ("Device") which is 
 *      integrated into Licensee's product; or
 * (ii) ONLY the Software driver source files ENC28J60.c and 
 *      ENC28J60.h ported to a non-Microchip device used in 
 *      conjunction with a Microchip ethernet controller for the 
 *      sole purpose of interfacing with the ethernet controller. 
 *
 * You should refer to the license agreement accompanying this 
 * Software for additional information regarding your rights and 
 * obligations.
 *
 * THE SOFTWARE AND DOCUMENTATION ARE PROVIDED "AS IS" WITHOUT 
 * WARRANTY OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT 
 * LIMITATION, ANY WARRANTY OF MERCHANTABILITY, FITNESS FOR A 
 * PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT SHALL 
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 *
 *
 * Author               Date        Comment
 *~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 * Nilesh Rajbharti     6/28/01     Original        (Rev 1.0)
 * Nilesh Rajbharti     2/9/02      Cleanup
 * Nilesh Rajbharti     5/22/02     Rev 2.0 (See version.log for detail)
 * Howard Schlunder     6/13/07     Changed to use timer without 
 *                                  writing for perfect accuracy.
********************************************************************/
#define __TICK_C

#include "TCPIP.h"

// Internal counter to store Ticks.
static DWORD dwInternalTicks = 0;

// 6-byte value to store Ticks.  Allows for use over longer periods of time.
static BYTE vTickReading[6];

static void GetTickCopy(void);
void HighISR(void);

/*****************************************************************************
  Function:
    void TickInit(void)

  Summary:
    Initializes the Tick manager module.

  Description:
    Configures the Tick module and any necessary hardware resources.

  Precondition:
    None

  Parameters:
    None

  Returns:
    None
    
  Remarks:
    This function is called only one during lifetime of the application.
  ***************************************************************************/
void TickInit(void)
{
    // Use Timer0
    // Initialize the time
    TMR0H = 0;
    TMR0L = 0;

    // Set up the timer interrupt
    INTCON2bits.TMR0IP = 1;     // High priority (MODIFIX: From low priority)
    INTCONbits.TMR0IF = 0;
    INTCONbits.TMR0IE = 1;      // Enable interrupt

    // Timer0 on, 16-bit, internal timer, 1:256 prescaler
    T0CON = 0x87;
}

/*****************************************************************************
  Function:
    static void GetTickCopy(void)

  Summary:
    Reads the tick value.

  Description:
    This function performs an interrupt-safe and synchronized read of the 
    48-bit Tick value.

  Precondition:
    None

  Parameters:
    None

  Returns:
    None
  ***************************************************************************/
static void GetTickCopy(void)
{
    // Perform an Interrupt safe and synchronized read of the 48-bit 
    // tick value
    do
    {
        INTCONbits.TMR0IE = 1;      // Enable interrupt
        Nop();
        INTCONbits.TMR0IE = 0;      // Disable interrupt
        vTickReading[0] = TMR0L;
        vTickReading[1] = TMR0H;
        *((DWORD*)&vTickReading[2]) = dwInternalTicks;
    } while(INTCONbits.TMR0IF);
    INTCONbits.TMR0IE = 1;          // Enable interrupt
}


/*****************************************************************************
  Function:
    DWORD TickGet(void)

  Summary:
    Obtains the current Tick value.

  Description:
    This function retrieves the current Tick value, allowing timing and
    measurement code to be written in a non-blocking fashion.  This function
    retrieves the least significant 32 bits of the internal tick counter, 
    and is useful for measuring time increments ranging from a few 
    microseconds to a few hours.  Use TickGetDiv256 or TickGetDiv64K for
    longer periods of time.

  Precondition:
    None

  Parameters:
    None

  Returns:
    Lower 32 bits of the current Tick value.
  ***************************************************************************/
DWORD TickGet(void)
{
    GetTickCopy();
    return *((DWORD*)&vTickReading[0]);
}

/*****************************************************************************
  Function:
    DWORD TickGetDiv256(void)

  Summary:
    Obtains the current Tick value divided by 256.

  Description:
    This function retrieves the current Tick value, allowing timing and
    measurement code to be written in a non-blocking fashion.  This function
    retrieves the middle 32 bits of the internal tick counter, 
    and is useful for measuring time increments ranging from a few 
    minutes to a few weeks.  Use TickGet for shorter periods or TickGetDiv64K
    for longer ones.

  Precondition:
    None

  Parameters:
    None

  Returns:
    Middle 32 bits of the current Tick value.
  ***************************************************************************/
DWORD TickGetDiv256(void)
{
    DWORD_VAL ret;

    GetTickCopy();
    ret.v[0] = vTickReading[1]; // Note: This copy must be done one 
    ret.v[1] = vTickReading[2]; // byte at a time to prevent misaligned 
    ret.v[2] = vTickReading[3]; // memory reads, which will reset the PIC.
    ret.v[3] = vTickReading[4];
    
    return ret.Val;
}

// MODIFIX: Removed the function TickGetDiv64K because not needed by eWicht.
// MODIFIX: Removed the function TickConvertToMilliseconds because not needed 
//          by eWicht. The ticks of eWicht are milliseconds!


// MODIFIX: The TickUpdate function is replaced by a high prior ISR routine.

// High prior Interrupt Service Routine

#pragma code high_vector=0x08
void high_interrupt (void)
{
    _asm GOTO HighISR _endasm
}
#pragma code

#pragma interrupt HighISR
void HighISR(void)
{
    // Increment internal high tick counter
    dwInternalTicks++;

    // Reset interrupt flag
    INTCONbits.TMR0IF = 0;
}

// MODIFIX: Removed the function _T1Interrupt because not needed by eWicht.

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