esos_pic24_tick.c

Go to the documentation of this file.

/*
 * "Copyright (c) 2008 Robert B. Reese, Bryan A. Jones, J. W. Bruce ("AUTHORS")"
 * All rights reserved.
 * (R. Reese, reese_AT_ece.msstate.edu, Mississippi State University)
 * (B. A. Jones, bjones_AT_ece.msstate.edu, Mississippi State University)
 * (J. W. Bruce, jwbruce_AT_ece.msstate.edu, Mississippi State University)
 *
 * Permission to use, copy, modify, and distribute this software and its
 * documentation for any purpose, without fee, and without written agreement is
 * hereby granted, provided that the above copyright notice, the following
 * two paragraphs and the authors appear in all copies of this software.
 *
 * IN NO EVENT SHALL THE "AUTHORS" BE LIABLE TO ANY PARTY FOR
 * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT
 * OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF THE "AUTHORS"
 * HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * THE "AUTHORS" SPECIFICALLY DISCLAIMS ANY WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
 * ON AN "AS IS" BASIS, AND THE "AUTHORS" HAS NO OBLIGATION TO
 * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS."
 *
 * Please maintain this header in its entirety when copying/modifying
 * these files.
 *
 *
 */

// Documentation for this file. If the \file tag isn't present,
// this file won't be documented.
/**
* \file
* Hardware-specific file (Microchip PIC24 Family) to generate
* the ESOS system tick functions.
*/

//#include    "esos_irq.h"
#include    "esos_pic24.h"

volatile  uint32_t        esos_tick_count;
volatile  uint8_t         sub_tick;

// prototype for the ESOS timer service function
extern void __esos_tmrSvcsExecute(void);

/****************************************************/
/*
* \brief Increments the ESOS system tick
*
* \pre  TMR1 is initialized with __esos_hw_InitSystemTick
*
* This ISR provides the mechanism for incrementing ESOS's
* 1.0ms system tick.  Using Timer 1, we can call this ISR
* every 1.0ms and increment esos_tick_count.  Or, we can
* have T1 call this ISR every X ms, and increment the
* value esos_tick_count by X
*
* \note The ESOS system tick will overflow in 2^32 msec
********************************************************/
void _ISRFAST _T1Interrupt (void) {
  esos_tick_count++;            // increment the ESOS system tick by
  _T1IF = 0;                    // clear the timer interrupt bit
  __esos_tmrSvcsExecute();      // let ESOS implement the S/w tmr service
}

/****************************************************/
/*
* \brief Initializes the ESOS system tick.
*
* \pre None assumed
*
* \post Sets up the PIC24 MCU's Timer1 to generate the 1.0ms tick
* required by ESOS.
*
* The (platform-independent) ESOS initialization code will
* call this function to setup and init the hardware (PIC24
* MCU, in this case) to create the required IRQs to generate
* the 1.0ms ESOS system tick.
*
* \note We can either generate an IRQ every 1.0ms or longer period,
* we just need to make sure that ISR that increments the tick
* count is consistent.
********************************************************/
void    __esos_hw_InitSystemTick(void) {
  // FOR NOW, we will init our usual PIC24 development setup here.
  //  THIS REALLY DOESN'T BELONG HERE!!!!!!!
  configClock();                //config clock

  // TODO: testing an experimental tick using an external watch xtal
  //       on the PIC24 secondary oscillator (SOSC) pins.
#if 1
  /**********************************************
   * USE FCY (instruction clock) to drive T1
   *      operate during IDLE, use a 64x prescaler,
   *      and the internal clock
   ********************************************************/
  T1CON = T1_IDLE_CON + T1_PS_1_64 + T1_SOURCE_INT;
  PR1 = MS_TO_TICKS(1, 64);        // 1 ms interrupt interval
#else
  /**********************************************
   * USE 32.768kHz watch xtal (SOSC) to drive T1
   *      operate during IDLE, use a 1x prescaler,
   *      and the secondary oscillator (must enable
   *      it via LPOSCEN in the OSCCON register)
   *      Not exactly 1ms tick (but neither is the
   *      instruction clock version)
   ********************************************************/
  // a local copy of OSCCON register to manipulate
  OSCCONBITS        OSCCONBITS_copy;
  asm("DISI #0x3FFF"); // Disable interrupts for a long time
  OSCCONBITS_copy = OSCCONbits;        // Copy OSCCON register bits
  OSCCONBITS_copy.LPOSCEN = 1;         // ENABLE secondary oscillator
  // First write high byte, containing new clock source NOSC
  __builtin_write_OSCCONH(BITS2BYTEH(OSCCONBITS_copy));
  // Then write low byte, requesting clock switch with OSWEN
  __builtin_write_OSCCONL(BITS2BYTEL(OSCCONBITS_copy));
  asm("DISI #0");     // Re-enable IRQs at the next instruction

  T1CON = T1_IDLE_CON + T1_PS_1_1 + T1_SOURCE_EXT + T1_SYNC_EXT_OFF;
  PR1 = 32;        // 32/32.768 = 0.9765625ms interrupt
#endif

  TMR1  = 0;                       // clear T1's count
  _T1IF = 0;                       // clear interrupt flag

  /* set T1's priority to be the highest possible for a PIC24 user IRQ
  ** User IRQs (if used) will be a lower IRQ priority, so the tick will
  ** get serviced in a timely manner
  */
  _T1IP = 7;
  _T1IE = 1;                       // enable the interrupt
  T1CONbits.TON = 1;               // turn on the timer

} // end __esos_hw_InitSystemTick()

/****************************************************/
/*
* \brief Returns the ESOS system tick count.
*
* \pre ESOS system tick is running/working.
*
* \return A 32-bit value of the number of ESOS system ticks
* since the system has booted.
*
********************************************************/
uint32_t   __esos_hw_GetSystemTickCount(void) {
  return  esos_tick_count;
}  // end __esos_hw_GetSystemTickCount()