+++ /dev/null
-/* Name: osccal.c
- * Author: Christian Starkjohann
- * Creation Date: 2008-04-10
- * Tabsize: 4
- * Copyright: (c) 2008 by OBJECTIVE DEVELOPMENT Software GmbH
- * License: GNU GPL v2 (see License.txt), GNU GPL v3 or proprietary (CommercialLicense.txt)
- */
-
-#include <avr/io.h>
-
-#include "usbdrv.h"
-
-#ifndef uchar
-#define uchar unsigned char
-#endif
-
-/* ------------------------------------------------------------------------- */
-/* ------------------------ Oscillator Calibration ------------------------- */
-/* ------------------------------------------------------------------------- */
-
-/* Calibrate the RC oscillator. Our timing reference is the Start Of Frame
- * signal (a single SE0 bit) repeating every millisecond immediately after
- * a USB RESET. We first do a binary search for the OSCCAL value and then
- * optimize this value with a neighboorhod search.
- */
-void calibrateOscillator(void)
-{
-uchar step = 128;
-uchar trialValue = 0, optimumValue;
-int x, optimumDev, targetValue = (unsigned)(1499 * (double)F_CPU / 10.5e6 + 0.5);
-
- /* do a binary search: */
- do{
- OSCCAL = trialValue + step;
- x = usbMeasureFrameLength(); /* proportional to current real frequency */
- if(x < targetValue) /* frequency still too low */
- trialValue += step;
- step >>= 1;
- }while(step > 0);
- /* We have a precision of +/- 1 for optimum OSCCAL here */
- /* now do a neighborhood search for optimum value */
- optimumValue = trialValue;
- optimumDev = x; /* this is certainly far away from optimum */
- for(OSCCAL = trialValue - 1; OSCCAL <= trialValue + 1; OSCCAL++){
- x = usbMeasureFrameLength() - targetValue;
- if(x < 0)
- x = -x;
- if(x < optimumDev){
- optimumDev = x;
- optimumValue = OSCCAL;
- }
- }
- OSCCAL = optimumValue;
-}
-/*
-Note: This calibration algorithm may try OSCCAL values of up to 192 even if
-the optimum value is far below 192. It may therefore exceed the allowed clock
-frequency of the CPU in low voltage designs!
-You may replace this search algorithm with any other algorithm you like if
-you have additional constraints such as a maximum CPU clock.
-For version 5.x RC oscillators (those with a split range of 2x128 steps, e.g.
-ATTiny25, ATTiny45, ATTiny85), it may be useful to search for the optimum in
-both regions.
-*/