rtctempcompensation.c

MSP430 RTC temperature compensation

/*
 *  Project                     MSP430 RTC Temperature Compensation
 *
 *  Software Name               FLASH-resident Main Application Software
 *
 *  Software Part Number        tbd
 *
 *  Module Filename             RtcTempCompensation.c
 *
 *  Module Description          RTC Temperature Compensation Source File
 *
 *  Module Language             ANSI C
 *
 *  Start Date                  13/10/2004      WH Molesworth   Initialed:
 *
 *  Check Date                  --/--/----      -               Initialed:
 *
 *  Last Code Mod. Date         09/10/2006      WH Molesworth   Initialed:
 *
 *  Revision Status             Version 1.00    (See Revision History below)
 *
 *  Manufacturer:               TI (Retro Watch Development Kit)
 *                              <www.ti.com>
 *
 *  Author:                     Hugh Molesworth    [e-mail]
 *                              Tel. US [phone]
 *
 *  Source by Hugh Molesworth. All Rights Reserved. Provided for guidance,
 *  feel free to use provided this notice is included.
 *
 *  Revision History:
 *  =================
 *
 *   Evaluation Release for TI MSP430 Design Contest
 *   ===============================================
 *   HM 00.01 09/10/2006 - Initial Release
 */

#include  <msp430x43x.h>
#include  "RtcTempCompensation.h"

// External references from original TI MSP430 Retro Watch Demo code:
extern void getTemp(void);       // Gets the current temperature
extern short bcd_add_short(short arg1,short arg2);
extern signed int tempF;         // Temperature variable
extern unsigned char seconds, minutes, hours; // The time values

#if defined (OPTION_USING_TEMPERATURE_COMPENSATION_FOR_RTC)

// The raw ADC Temperature value for the later compensation
uint16 SampledAdcRawValue = 0;

volatile byte UpdateTempCorrectionFlag = 0;

const byte FrequencyCorrectionTable[];


// Initialize RTC temperature cal index at (typically) 25 degrees C
uint16 RtcCorrectionTime;
//volatile byte RtcCorrectionIndex = CENTER_RTC_CALIBRATION_INDEX;

/*
 * RTC Time Error Analysis
 * =======================
 * There are 4 primary sources of error in any crystal-derived RTC:
 *
 * 1. Initial frequency error, usually expressed in parts-per-million (ppm),
 *    typically +-20ppm (53 secs/month) or +-5ppm (13 secs/month). Cheaper
 *    crystals can be as much as +-100ppm (265 secs/month).
 * 2. Load capacitance error (perhaps 10 secs/month), and delta load
 *    capacitance error, the latter capacitance change due to temperature,
 *    which is small enough to neglect.
 * 3. Temperature-dependant error from the typically 25癈 nominal, usually
 *    expressed in ppm/