clean up osccal

1 files changed, 228 insertions, 0 deletions

diff --git a/firmware/osccalASM.S b/firmware/osccalASM.S
new file mode 100644
index 0000000..9a317f1
--- /dev/null
+++ b/firmware/osccalASM.S
@@ -0,0 +1,228 @@
+/* Name: osccalASM.S
+ * Author: cpldcpu@gmail.com
+ * Creation Date: 2013-11-3
+ * Tabsize: 4
+ * License: GNU GPL v2 (see License.txt), GNU GPL v3 or proprietary (CommercialLicense.txt)
+ */
+
+/* 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. 
+ *
+ *
+ * Benefits:
+ *	  - Codesize reduced by 90 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.
+ */
+ 
+
+#define __SFR_OFFSET 0      /* used by avr-libc's register definitions */
+#include "./usbdrv/usbdrv.h"         /* for common defs */
+
+#ifdef __IAR_SYSTEMS_ASM__
+/* Register assignments for usbMeasureFrameLengthDecreasing on IAR cc */
+/* Calling conventions on IAR:
+ * First parameter passed in r16/r17, second in r18/r19 and so on.
+ * Callee must preserve r4-r15, r24-r29 (r28/r29 is frame pointer)
+ * Result is passed in r16/r17
+ * In case of the "tiny" memory model, pointers are only 8 bit with no
+ * padding. We therefore pass argument 1 as "16 bit unsigned".
+ */
+
+//Untested
+
+#   define i		r20	
+#   define opV		r19
+#   define opD		r18
+#   define try		r21
+#   define stp		r22
+
+#   define cnt16L   r30
+#   define cnt16H   r31
+
+
+#else  /* __IAR_SYSTEMS_ASM__ */ 
+/* Register assignments for usbMeasureFrameLength on gcc */
+/* Calling conventions on gcc:
+ * First parameter passed in r24/r25, second in r22/23 and so on.
+ * Callee must preserve r1-r17, r28/r29
+ * Result is passed in r24/r25
+ */
+
+#   define i		r20	
+#   define opV		r19
+#   define opD		r18
+#   define try		r27
+#   define stp		r26
+#   define cnt16L   r24
+#   define cnt16H   r25
+#endif
+#   define cnt16    cnt16L
+
+; extern void calibrateOscillatorASM(void);
+
+.global calibrateOscillatorASM
+calibrateOscillatorASM:
+
+	cli
+	ldi		opD, 255	
+
+	ldi		try, 128	; calibration start value
+	ldi		stp, 64		; initial step width
+	ldi		i, 10		; 10 iterations
+
+usbCOloop:
+
+	out		OSCCAL, try
+	nop
+
+	; Delay values = F_CPU * 999e-6 / 5 + 0.5
+	
+#if (F_CPU == 16500000)
+	ldi		cnt16L, lo8(3297)
+	ldi		cnt16H, hi8(3297)
+#elif (F_CPU == 12800000)
+	ldi		cnt16L, lo8(2557)
+	ldi		cnt16H, hi8(2557)
+#else
+	#error "calibrateOscillatorASM: no delayvalues defined for this F_CPU setting"
+#endif
+
+usbCOWaitStrobe:            ; first wait for D- == 0 (idle strobe)
+    sbic    USBIN, USBMINUS ;
+    rjmp    usbCOWaitStrobe ;
+usbCOWaitIdle:              ; then wait until idle again
+    sbis    USBIN, USBMINUS ;1 wait for D- == 1
+    rjmp    usbCOWaitIdle   ;2
+usbCOWaitLoop:
+	sbiw	cnt16,1			;[0] [5]
+    sbic    USBIN, USBMINUS ;[2] 
+    rjmp    usbCOWaitLoop   ;[3]
+
+	sbrs	cnt16H, 7		;delay overflow?
+	rjmp	usbCOclocktoolow
+	sub		try, stp
+	neg		cnt16L
+	rjmp	usbCOclocktoohigh
+usbCOclocktoolow:
+	add		try, stp
+usbCOclocktoohigh:
+	lsr		stp
+	brne	usbCOnoneighborhoodsearch
+	cp		opD, cnt16L
+	brcs	usbCOnoimprovement
+	in		opV, OSCCAL
+	mov		opD, cnt16L
+usbCOnoimprovement:
+	ldi		stp, 1
+usbCOnoneighborhoodsearch:
+	subi	i, 1
+	brne	usbCOloop
+
+	out		OSCCAL, opV
+	nop
+	sei
+    ret
+
+#undef i
+#undef opV
+#undef opD
+#undef try
+#undef stp
+#undef cnt16
+#undef cnt16L
+#undef cnt16H
+
+/* ------------------------------------------------------------------------- */
+/* ------ Original C Implementation of improved calibrateOscillator -------- */
+/* ----------------------   for Reference only ----------------------------- */
+/* ------------------------------------------------------------------------- */
+
+#if 0
+void    calibrateOscillator(void)
+{
+	uchar       step, trialValue, optimumValue;
+	int         x, targetValue;
+	uchar		optimumDev;
+	uchar		i,xl;
+	
+	targetValue = (unsigned)((double)F_CPU * 999e-6 / 5.0 + 0.5);  /* Time is measured in multiples of 5 cycles. Target is 0.999µs */
+    optimumDev = 0xff;   
+  //  optimumValue = OSCCAL; 
+	step=64;
+	trialValue = 128;
+	
+	cli(); // disable interrupts
+	
+	/*
+		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;
+			xl=(uchar)-x;
+		}
+		else                  /* frequency too low */
+		{
+			trialValue += step;			
+			xl=(uchar)x;
+		}
+		
+		/*
+			Halve stepwidth to perform binary search. At step=1 the mode changes to neighbourhood search.
+			Once the neighbourhood search stage is reached, x will be smaller than +-255, hence more code can be
+			saved by only working with the lower 8 bits.
+		*/
+		
+		step >>= 1;
+		
+		if (step==0)   // Enter neighborhood search mode
+		{
+			step=1;			
+			if(xl <= optimumDev){
+				optimumDev = xl;
+				optimumValue = OSCCAL;
+			}
+		}
+	}
+
+	OSCCAL = optimumValue;
+	asm volatile(" NOP");
+	
+	sei(); // enable interrupts
+}
+#endif
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