calib_32kHz.c File Reference

---

Detailed Description

Main routine and all functions.

Application note:

AVR055: Using a 32 kHz crystal to calibrate the internal RC oscillator

Documentation

For comprehensive code documentation, supported compilers, compiler settings and supported devices see readme.html

Author:

Atmel Corporation: http://www.atmel.com
Support email: avr@atmel.com

Name

RELEASE_1_1

Revision

1.2

RCSfile

calib_32kHz.c,v

Date

2006/02/17 12:49:26

Definition in file calib_32kHz.c.

#include "calib_values.h"
#include "device_specific.h"
#include <inavr.h>
#include <ioavr.h>

Include dependency graph for calib_32kHz.c:

Go to the source code of this file.

Functions
void	BinarySearch (unsigned int ct)
	The binary search method.
void	CalibrateInternalRc (void)
	Calibration function.
void	CalibrationInit (void)
	Initializes the calibration.
unsigned int	Counter (void)
	The Counter function.
void	main (void)
	Program entry point.
void	NeighborSearch (void)
	The neighbor search method.
Variables
unsigned char	bestCountDiff = 0xFF
	The lowest difference between desired and measured counter value.
unsigned char	bestCountDiff_first
	Stores the lowest difference between desired and measured counter value for the first search.
unsigned char	bestOSCCAL
	The OSCCAL value corresponding to the bestCountDiff.
unsigned char	bestOSCCAL_first
	Stores the OSCCAL value corresponding to the bestCountDiff for the first search.
unsigned int	calibration
	Calibration status.
unsigned char	calStep
	The binary search step size.
unsigned int	countVal
	The desired counter value.
unsigned char	neighborsSearched
	Holds the number of neighbors searched.
signed char	sign
	Stores the direction of the binary step (-1 or 1).

---

Function Documentation

void BinarySearch (  unsigned int  ct  )

The binary search method. This function uses the binary search method to find the correct OSSCAL value. Definition at line 200 of file calib_32kHz.c. References calibration, calStep, countVal, FINISHED, NOP, and sign. Referenced by CalibrateInternalRc(). { if (ct > countVal) // Check if count is larger than desired value { sign = -1; // Saves the direction OSCCAL -= calStep; // Decrease OSCCAL if count is too high NOP(); } else if (ct < countVal) // Opposite procedure for lower value { sign = 1; OSCCAL += calStep; NOP(); } else // Perfect match, OSCCAL stays unchanged { calibration = FINISHED; } calStep >>= 1; }

void CalibrateInternalRc (  void   )

Calibration function. Performs the calibration according to calibration method chosen. Compares different calibration results in order to achieve optimal results. Definition at line 116 of file calib_32kHz.c. References ABS, bestCountDiff, bestOSCCAL, BinarySearch(), calibration, calStep, Counter(), countVal, FINISHED, NeighborSearch(), neighborsSearched, NOP, and RUNNING. Referenced by main(). { unsigned int count; #ifdef CALIBRATION_METHOD_SIMPLE // Simple search method unsigned char cycles = 0x80; do{ count = Counter(); if (count > countVal) OSCCAL--; // If count is more than count value corresponding to the given frequency: NOP(); // - decrease speed if (count < countVal) OSCCAL++; NOP(); // If count is less: - increase speed if (count == countVal) cycles=1; } while(--cycles); // Calibrate using 128(0x80) calibration cycles #else // Binary search with or without neighbor search unsigned char countDiff; unsigned char neighborSearchStatus = FINISHED; while(calibration == RUNNING){ count = Counter(); // Counter returns the count value after external ticks on XTAL if (calStep != 0) { BinarySearch(count); // Do binary search until stepsize is zero } else { if(neighborSearchStatus == RUNNING) { countDiff = ABS((signed int)count-(signed int)countVal); if (countDiff < bestCountDiff) // Store OSCCAL if higher accuracy is achieved { bestCountDiff = countDiff; bestOSCCAL = OSCCAL; } NeighborSearch(); // Do neighbor search } else // Prepare and start neighbor search { #ifdef CALIBRATION_METHOD_BINARY_WITHOUT_NEIGHBOR // No neighbor search if deselected calibration = FINISHED; countDiff = ABS((signed int)count-(signed int)countVal); bestCountDiff = countDiff; bestOSCCAL = OSCCAL; #else neighborSearchStatus = RUNNING; // Do neighbor search by default neighborsSearched = 0; countDiff = ABS((signed int)count-(signed int)countVal); bestCountDiff = countDiff; bestOSCCAL = OSCCAL; #endif } } } #endif } Here is the call graph for this function:

void CalibrationInit (  void   )

Initializes the calibration. Computes the count value needed to compare the desired internal oscillator speed with the external watch crystal, and sets up the asynchronous timer. Definition at line 101 of file calib_32kHz.c. References COMPUTE_COUNT_VALUE, DEFAULT_OSCCAL, NOP, and SETUP_ASYNC_TIMER. Referenced by main(). { COMPUTE_COUNT_VALUE(); // Computes countVal for use in the calibration OSCCAL = DEFAULT_OSCCAL; NOP(); SETUP_ASYNC_TIMER(); // Asynchronous timer setup }

unsigned int Counter (  void   )

The Counter function. This function increments a counter for a given ammount of ticks on on the external watch crystal. Definition at line 182 of file calib_32kHz.c. References EXTERNAL_TICKS. Referenced by CalibrateInternalRc(). { unsigned int cnt; cnt = 0; // Reset counter TIMER = 0x00; // Reset async timer/counter while (ASSR & ((1<<OUTPUT_COMPARE_UPDATE_BUSY)|(1<<TIMER_UPDATE_BUSY)|(1<<ASYNC_TIMER_CONTROL_UPDATE_BUSY))); // Wait until async timer is updated (Async Status reg. busy flags). do{ // cnt++: Increment counter - the add immediate to word (ADIW) takes 2 cycles of code. cnt++; // Devices with async TCNT in I/0 space use 1 cycle reading, 2 for devices with async TCNT in extended I/O space } while (TIMER < EXTERNAL_TICKS); // CPI takes 1 cycle, BRCS takes 2 cycles, resulting in: 2+1(or 2)+1+2=6(or 7) CPU cycles return cnt; // NB! Different compilers may give different CPU cycles! } // Until 32.7KHz (XTAL FREQUENCY) * EXTERNAL TICKS

void main (  void   )

Program entry point. Main initializes all subsystems, prepares and starts calibration according to the calibration method chosen, and the device specific oscillator characteristics. Ends in an eternal loop. Definition at line 64 of file calib_32kHz.c. References bestCountDiff, bestCountDiff_first, bestOSCCAL, bestOSCCAL_first, CalibrateInternalRc(), CalibrationInit(), DEFAULT_OSCCAL_HIGH, NOP, and PREPARE_CALIBRATION. { CalibrationInit(); // Initiates calibration PREPARE_CALIBRATION(); // Sets initial stepsize and sets calibration state to "running" CalibrateInternalRc(); // Calibrates to selected frequency #ifndef CALIBRATION_METHOD_SIMPLE // If simple search method is chosen, there is no need to do two calibrations. #ifdef TWO_RANGES // For devices with splitted OSCCAL register. if (bestCountDiff != 0x00) // Do not do a second search if perfect match { OSCCAL = DEFAULT_OSCCAL_HIGH; // Sets search range to upper part of OSCCAL NOP(); bestOSCCAL_first = bestOSCCAL; // Save OSCCAL value and count difference achieved in first calibration bestCountDiff_first = bestCountDiff; PREPARE_CALIBRATION(); // Search performed in lower OSCCAL range, perform search in upper OSCCAl range CalibrateInternalRc(); // Perform a second search in upper part of OSCCAL if (bestCountDiff > bestCountDiff_first) // Check which search gave the best calibration { OSCCAL = bestOSCCAL_first; // First calibration is more accurate and OSCCAL is written accordingly NOP(); } } #endif #endif for(;;) { } } Here is the call graph for this function:

void NeighborSearch (  void   )

The neighbor search method. This function uses the neighbo search method to improve binary search result. Will always be called with a binary search prior to it. Definition at line 228 of file calib_32kHz.c. References bestOSCCAL, calibration, FINISHED, neighborsSearched, NOP, and sign. Referenced by CalibrateInternalRc(). { neighborsSearched++; if (neighborsSearched == 4) // Finish if 3 neighbors searched { OSCCAL = bestOSCCAL; calibration = FINISHED; } else { OSCCAL+=sign; NOP(); } }

---

Variable Documentation

unsigned char bestCountDiff = 0xFF

The lowest difference between desired and measured counter value. Definition at line 35 of file calib_32kHz.c. Referenced by CalibrateInternalRc(), and main().

unsigned char bestCountDiff_first

Stores the lowest difference between desired and measured counter value for the first search. Definition at line 37 of file calib_32kHz.c. Referenced by main().

unsigned char bestOSCCAL

The OSCCAL value corresponding to the bestCountDiff. Definition at line 39 of file calib_32kHz.c. Referenced by CalibrateInternalRc(), main(), and NeighborSearch().

unsigned char bestOSCCAL_first

Stores the OSCCAL value corresponding to the bestCountDiff for the first search. Definition at line 41 of file calib_32kHz.c. Referenced by main().

unsigned int calibration

Calibration status. Definition at line 45 of file calib_32kHz.c. Referenced by BinarySearch(), CalibrateInternalRc(), and NeighborSearch().

unsigned char calStep

The binary search step size. Definition at line 33 of file calib_32kHz.c. Referenced by BinarySearch(), and CalibrateInternalRc().

unsigned int countVal

The desired counter value. Definition at line 43 of file calib_32kHz.c. Referenced by BinarySearch(), and CalibrateInternalRc().

unsigned char neighborsSearched

Holds the number of neighbors searched. Definition at line 31 of file calib_32kHz.c. Referenced by CalibrateInternalRc(), and NeighborSearch().

signed char sign

Stores the direction of the binary step (-1 or 1). Definition at line 47 of file calib_32kHz.c. Referenced by BinarySearch(), and NeighborSearch().

---