nes-proj/cpu/mc1322x/lib/rtc.c

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/*
* Copyright (c) 2010, Mariano Alvira <mar@devl.org> and other contributors
* to the MC1322x project (http://mc1322x.devl.org)
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the Institute nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* This file is part of libmc1322x: see http://mc1322x.devl.org
* for details.
*
*
*/
#include <mc1322x.h>
#include <stdlib.h>
#include "rtc.h"
/* Define USE_32KHZ in board.h to start and use the 32 KHz
oscillator, otherwise the 2 KHz ring oscillator is used. */
int rtc_freq = 0;
static int __use_32khz = 0;
/* Init RTC */
void rtc_init_osc(int use_32khz)
{
__use_32khz = use_32khz;
if (use_32khz)
{
uint32_t old;
/* You have to hold its hand with this one */
/* once you start the 32KHz crystal it can only be
* stopped with a reset (hard or soft). */
/* first, disable the ring osc */
CRM->RINGOSC_CNTLbits.ROSC_EN = 0;
/* enable the 32kHZ crystal */
CRM->XTAL32_CNTLbits.XTAL32_EN = 1;
/* set the XTAL32_EXISTS bit */
/* the datasheet says to do this after you check that RTC_COUNT
is changing, but it is not correct; it needs to be set first */
CRM->SYS_CNTLbits.XTAL32_EXISTS = 1;
old = CRM->RTC_COUNT;
while (CRM->RTC_COUNT == old)
continue;
/* RTC has started up */
rtc_freq = 32768;
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}
else
{
/* Enable ring osc */
CRM->RINGOSC_CNTLbits.ROSC_EN = 1;
CRM->XTAL32_CNTLbits.XTAL32_EN = 0;
/* Set default tune values from datasheet */
CRM->RINGOSC_CNTLbits.ROSC_CTUNE = 0x6;
CRM->RINGOSC_CNTLbits.ROSC_FTUNE = 0x17;
/* Trigger calibration */
rtc_calibrate();
}
}
uint32_t __rtc_try(int loading, int timeout)
{
/* Total loading is
ctune * 1000 fF + ftune * 160 fF
ctune = 0-15
ftune = 0-31
max = 19960 fF
*/
#define RTC_LOADING_MIN 0
#define RTC_LOADING_MAX 19960
/* The fine tune covers a range larger than a single coarse
step. Check all coarse steps within the fine tune range to
find the optimal CTUNE, FTUNE pairs. */
#define CTUNE_MAX 15
#define FTUNE_MAX 31
#define CSTEP 1000
#define FSTEP 160
#define MAX_F (FSTEP*FTUNE_MAX) /* actually lcm(CSTEP,FSTEP) would be better,
but in this case it's basically the same */
int ctune;
int ftune;
int ctune_start = (loading - MAX_F) / CSTEP;
int ctune_end = loading / CSTEP;
int best_err = loading, best_ctune = 0, best_ftune = 0;
uint32_t count;
if (ctune_start < 0) ctune_start = 0;
if (ctune_end > CTUNE_MAX) ctune_end = CTUNE_MAX;
for (ctune = ctune_start; ctune <= ctune_end; ctune++)
{
int this_loading, this_err;
ftune = ((loading - (ctune * CSTEP)) + (FSTEP / 2)) / FSTEP;
if (ftune < 0) ftune = 0;
if (ftune > FTUNE_MAX) ftune = FTUNE_MAX;
this_loading = ctune * CSTEP + ftune * FSTEP;
this_err = abs(this_loading - loading);
if (this_err < best_err) {
best_err = this_err;
best_ctune = ctune;
best_ftune = ftune;
}
}
// printf("requested loading %d, actual loading %d\r\n", loading,
// best_ctune * CSTEP + best_ftune * FSTEP);
/* Run the calibration */
CRM->RINGOSC_CNTLbits.ROSC_CTUNE = best_ctune;
CRM->RINGOSC_CNTLbits.ROSC_FTUNE = best_ftune;
CRM->CAL_CNTLbits.CAL_TIMEOUT = timeout;
CRM->STATUSbits.CAL_DONE = 1;
CRM->CAL_CNTLbits.CAL_EN = 1;
while (CRM->STATUSbits.CAL_DONE == 0)
continue;
/* Result should ideally be close to (REF_OSC * (timeout / 2000)) */
count = CRM->CAL_COUNT;
if (count == 0) count = 1; /* avoid divide by zero problems */
return count;
}
/* Calibrate the ring oscillator */
void rtc_calibrate(void)
{
/* Just bisect a few times. Our best tuning accuracy is about
1/500 of the full scale, so doing this 8-9 times is about
as accurate as we can get */
int i;
int low = RTC_LOADING_MIN, high = RTC_LOADING_MAX;
int mid;
uint32_t count;
if (__use_32khz) {
rtc_freq = 32768;
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return;
}
#define TIMEOUT 100 /* 50 msec per attempt */
for (i = 0; i < 16; i++)
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{
mid = (low + high) / 2;
count = __rtc_try(mid, TIMEOUT);
// careful about overflow
rtc_freq = REF_OSC / ((count + TIMEOUT/2) / TIMEOUT);
if (rtc_freq > 2048)
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low = mid; // increase loading
else
high = mid; // decrease loading
}
// printf("RTC calibrated to %d Hz\r\n", rtc_freq);
}
/* Delay for the specified number of milliseconds by polling RTC */
void rtc_delay_ms(uint32_t msec)
{
uint32_t start;
start = CRM->RTC_COUNT;
while ((CRM->RTC_COUNT - start) < ((msec * rtc_freq) / 1000))
continue;
}