/* Name: osccalASM.S v1.1
* Author: cpldcpu@gmail.com
* Creation Date: 2013-11-3
* Update : 2014-01-4
*
* 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.
* Update 2014-01-4
* - Added an initial sync-state, which will discard the first delay measurement.
* This allows to call this routine before or during the SE0 bus reset without
* corrupting OSCCAL.
* - Removed CLI/SEI to allow more flexibility.
*
*
* 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:
ldi opD, 255
ldi try, 128 ; calibration start value
ldi stp, 0 ; initial step width=0 for sync phase (first delay is discarded)
ldi i, 11 ; 11 iterations (1x sync, 7x binary search, 3x neighbourhood)
usbCOloop:
out OSCCAL, try
; 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)
#elif (F_CPU == 12000000)
ldi cnt16L, lo8(2398)
ldi cnt16H, hi8(2398)
#elif (F_CPU == 16000000)
ldi cnt16L, lo8(3197)
ldi cnt16H, hi8(3197)
#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:
#ifdef __AVR_ATtiny10__
subi cnt16L,1 ;[0] [5]
sbci cnt16H,0 ;[1]
#else
sbiw cnt16,1 ;[0] [5]
#endif
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 ; stp = 0 in first iteration (sync)
; stp = 2^x (x=0..6) during binary search,
; stp = 1 during neighbourhood search
brne usbCObinarysearch
ldi stp, 64 ; stp=64 to initiate binary search.
; If we are in neighbourhood search (c=1), it is changed to 1 below
brcc usbCObinarysearch
cp opD, cnt16L
brcs usbCOnoimprovement
in opV, OSCCAL
mov opD, cnt16L
usbCOnoimprovement:
ldi stp, 1 ; stp=1 to continue with neighbourhood search
usbCObinarysearch:
subi i, 1
brne usbCOloop
out OSCCAL, opV
; nop
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");
}
#endif
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