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authorcpldcpu <cpldcpu@gmail.com>2013-11-04 00:22:17 +0100
committercpldcpu <cpldcpu@gmail.com>2013-11-04 00:22:17 +0100
commitf3456ea1cfc56ebfa1fcea33be93856c0a71df37 (patch)
tree40fdff10bbd1bb0229cbb27062790ea87a18c041 /firmware/libs-device/osccal.c
parent5b7617bfb1763f14a9e1e8792447d75cd076d2fa (diff)
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Updated USB Driver, nanite, oscal
Diffstat (limited to 'firmware/libs-device/osccal.c')
-rw-r--r--firmware/libs-device/osccal.c114
1 files changed, 85 insertions, 29 deletions
diff --git a/firmware/libs-device/osccal.c b/firmware/libs-device/osccal.c
index 939d5c3..b8d1bb5 100644
--- a/firmware/libs-device/osccal.c
+++ b/firmware/libs-device/osccal.c
@@ -8,49 +8,105 @@
*/
#include <avr/io.h>
-
#ifndef uchar
#define uchar unsigned char
#endif
+int usbMeasureFrameLengthDecreasing(int);
+
/* ------------------------------------------------------------------------- */
/* ------------------------ 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.
+ * a USB RESET.
+ *
+ *
+ * Optimized version by cpldcpu@gmail.com, Nov 3rd 2013.
+ *
+ * Benefits:
+ * - Codesize reduced by 54 bytes.
+ * - Improved robustness due to removing timeout from frame length measurement and
+ * inserted NOP after OSCCAL writes.
+ *
+ * Changes:
+ * - The new routine performs a combined binary and neighborhood search
+ * in a single loop.
+ * Note that the neighborhood search is necessary due to the quasi-monotonic
+ * nature of OSCCAL. (See Atmel application note AVR054).
+ * - Inserted NOP after writes to OSCCAL to avoid CPU errors during oscillator
+ * stabilization.
+ * - Implemented new routine to measure frame time "usbMeasureFrameLengthDecreasing".
+ * This routine takes the target time as a parameter and returns the deviation.
+ * - usbMeasureFrameLengthDecreasing measures in multiples of 5 cycles and is thus
+ * slighly more accurate.
+ * - usbMeasureFrameLengthDecreasing does not support time out anymore. The original
+ * implementation returned zero in case of time out, which would have caused the old
+ * calibrateOscillator() implementation to increase OSSCAL to 255, effictively
+ * overclocking and most likely crashing the CPU. The new implementation will enter
+ * an infinite loop when no USB activity is encountered. The user program should
+ * use the watchdog to escape from situations like this.
+ *
+ * This routine will work both on controllers with and without split OSCCAL range.
+ * The first trial value is 128 which is the lowest value of the upper OSCCAL range
+ * on Attiny85 and will effectively limit the search to the upper range, unless the
+ * RC oscillator frequency is unusually high. Under normal operation, the highest
+ * tested frequency setting is 192. This corresponds to ~20 Mhz core frequency and
+ * is still within spec for a 5V device.
*/
+
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;
+ uchar step, trialValue, optimumValue;
+ int x, optimumDev, targetValue;
+ uchar i;
+
+ targetValue = (unsigned)((double)F_CPU * 999e-6 / 5.0 + 0.5); /* Time is measured in multiples of 5 cycles. Target is 0.999µs */
+ optimumDev = 0x7f00; // set to high positive value
+ optimumValue = OSCCAL;
+ step=64;
+ trialValue = 128;
+
+ /*
+ Performs seven iterations of a binary search (stepwidth decreasing9
+ with three additional steps of a neighborhood search (step=1, trialvalue will oscillate around target value to find optimum)
+ */
+
+ for(i=0; i<10; i++){
+ OSCCAL = trialValue;
+ asm volatile(" NOP");
+
+ x = usbMeasureFrameLengthDecreasing(targetValue);
+
+ if(x < 0) /* frequency too high */
+ {
+ trialValue -= step;
+ x = -x;
+ }
+ else /* frequency too low */
+ {
+ trialValue += step;
+ }
+
+ /*
+ Halve stepwidth to perform binary search. Logical oring with 1 to ensure step is never equal to zero.
+ This results in a neighborhood search with stepwidth 1 after binary search is finished.
+ */
+
+ step >>= 1;
+ step |=1;
+
+ if(x < optimumDev){
+ optimumDev = x;
+ optimumValue = OSCCAL;
+ }
+ }
+
+ OSCCAL = optimumValue;
+ asm volatile(" NOP");
}
+
/*
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