main.c中start_kernel()函数调用linux/arch/arm/kernel/time.c 中的time_init(),
time_init函数调用include/asm-arm/arch-s3c2410/time.h中的setup_timer();
其具体内容见下面函数细节。
The xtime_lock is not only serializing the xtime read/writes but it's also
serializing all accesses to the global NTP variables now.
linux/kernel/timer.c中定义的是一些全局的关于timer的变量和函数。
long tick = (1000000 + HZ/2) / HZ; /* timer interrupt period */
/* The current time */
struct timeval xtime __attribute__ ((aligned (16)));
linux/arch/arm/kernel/time.c
/*
* hook for setting the RTC's idea of the current time.
*/
int (*set_rtc)(void) = dummy_set_rtc;//初始化设置为一个空函数.
/*
* hook for getting the time offset. Note that it is
* always called with interrupts disabled.
*/
unsigned long (*gettimeoffset)(void) = dummy_gettimeoffset;//初始化设置为一个空函数.
/*
* Handle kernel profile stuff...
*/
static inline void do_profile(struct pt_regs *regs)
/*
* If we have an externally synchronized linux clock, then update
* CMOS clock accordingly every ~11 minutes. set_rtc() has to be
* called as close as possible to 500 ms before the new second
* starts.
*/
如果time_status & STA_UNSYNC为1,或者set_rtc函数为NULL,返回;
如果next_rtc_update(long类型的)大于0且当前的秒数还没有到next_rtc_update,返回；
还有个条件，关于当前xtime.tv_usec的判断，没看懂；
set_rtc(),失败，则在下一分钟继续更新next_rtc_update = xtime.tv_sec + 60;
成功，则过11分钟更新，next_rtc_update = xtime.tv_sec + 660;
static inline void do_set_rtc(void)
void (*leds_event)(led_event_t) = dummy_leds_event;//初始化设置为一个空函数.
static void do_leds(void)
void do_gettimeofday(struct timeval *tv)
void do_settimeofday(struct timeval *tv)
static struct irqaction timer_irq = {
name: "timer",
};
/*
* This must cause the timer to start ticking.
* It doesn't have to set the current time though
* from an RTC - it can be done later once we have
* some buses initialised.
*/
void __init time_init(void)
在include/asm-arm/arch-s3c2410/time.h中重要函数和常量定义
#define epoch 1970
static const unsigned char days_in_mo[] =
{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
#define BCD_TO_BIN(val) ((val)=((val)&15) + ((val)>>4)*10)
#define BIN_TO_BCD(val) ((val)=(((val)/10)<<4) + (val)%10)
判断是否为闰年
#define is_leap(year) \
((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
#define RTC_LEAP_YEAR 2000
获取rtc时间，并Converts Gregorian date to seconds since 1970-01-01 00:00:00.然后返回
其中调用了linux/time.h中的mktime(..)其中转化算法好象是first published by Gauss
unsigned long s3c2410_get_rtc_time(void);
/*
* Converts seconds since 1970-01-01 00:00:00 to Gregorian date.
* 返回值到rtc_time结构中
*/
static void decodetime (unsigned long t, struct rtc_time *tval)
安装rtc,根据系统中的xtime.tv_sec，更新rtc时钟。
调用了decodetime把1970年来的second值转换为Gre时间(from 1900)，并转化为BCD码，写入时钟芯片.函数仅返回0，无任何错误返回..用于sync update rtc
int s3c2410_set_rtc(void)
好象是返回用去了多少秒?
static unsigned long s3c2410_gettimeoffset(void)
//时钟中断服务例程,调用do_leds,do_set_rtc,do_timer
static void s3c2410_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
/* Unit of 'freq' is khz */
struct timer_counts {
unsigned int freq;
unsigned int count;
};
/*到底是怎么转化的？？？？？
* priod = (prescaler value + 1) * (divider value) * buffer count / PCLK = 10 ms
*
* e.g.; PCLK = 50 Mhz
* 10 ms = (15 + 1) * 2 * 15625 / (50000 * 1000)
* 15626 = 10 ms * (50000 * 1000) / 2 / (15 + 1)
*
* Other values
* 5156 = 10 ms * ( 16.5 * 1,000,000) / 2 / (15+1)
* 6250 = 10 ms * ( 20 * 1,000,000) / 2 / (15+1)
* 10312 = 10 ms * ( 33 * 1,000,000) / 2 / (15+1)
* 20625 = 10 ms * ( 66 * 1,000,000) / 2 / (15+1)
* 21875 = 10 ms * ( 70 * 1,000,000) / 2 / (15+1)
* 23437 = 10 ms * ( 75 * 1,000,000) / 2 / (15+1)
* 25000 = 10 ms * ( 80 * 1,000,000) / 2 / (15+1)
* 28125 = 10 ms * ( 90 * 1,000,000) / 2 / (15+1)
* 31250 = 10 ms * ( 100 * 1,000,000) / 2 / (15+1)
*/
struct timer_counts count_values[] = {
{ 16500, 5156 },
{ 20000, 6250 },
{ 33000, 10312 },
{ 45000, 14063 },
{ 48000, 15000 },
{ 50000, 15626 },
{ 50700, 15844 },
{ 66000, 20625 },
{ 70000, 21875 },
{ 75000, 23437 },
{ 80000, 25000 },
{ 90000, 28125 },
{ 100000, 31250 },
{ 0, 0 } /* last entry */
};
安装Timer
static inline void setup_timer(void)
{
struct timer_counts *timer_count = count_values;
unsigned long pclk;
设置timer函数吧:gettimeoffset和set_rtc函数都定义在/*linux/arch/arm/kernel/time.c*/
gettimeoffset = s3c2410_gettimeoffset;/*linux/arch/arm/kernel/time.c*/get us
set_rtc = s3c2410_set_rtc;
xtime.tv_sec = s3c2410_get_rtc_time();//就在本文件中定义
/* set timer interrupt */在哪里定义的这些宏？
TCFG0 = (TCFG0_DZONE(0) | TCFG0_PRE1(15) | TCFG0_PRE0(0));
pclk = s3c2410_get_bus_clk(GET_PCLK)/1000;获得总线时钟PCLK/1000作为frequence
while (timer_count != 0) { 循环查找相同的freq，找到了就安装Timer 4初值.
if (pclk == timer_count->freq) {
printk("DEBUG: timer count %d\n", timer_count->count);
TCNTB4 = timer_count->count;//TCNTB4--Timer 4
break;
}
timer_count++;
}
如果没有找到对应的frep,就假定系统的PCLK为50Mhz,安装timer4
if (timer_count == 0) {
/* Error, assume that PCLK is 50 Mhz */
TCNTB4 = 15626; /* down-counter, maximum value is 65535 (2^16) */
}
// TCNTB4=s3c2410_get_bus_clk(GET_PCLK)/1000; //add by HHTECH
初始化Timer control register,关闭计数
TCON = (TCON_4_AUTO | TCON_4_UPDATE | COUNT_4_OFF);
安装timer中断服务程序
timer_irq.handler = s3c2410_timer_interrupt;//timer_irq定义在/*linux/arch/arm/kernel/time.c*/
setup_arm_irq(IRQ_TIMER4, &timer_irq);
TCON = (TCON_4_AUTO | COUNT_4_ON);//开始计数
}
EXPORT_SYMBOL(s3c2410_get_rtc_time);
EXPORT_SYMBOL(s3c2410_set_rtc);
1.
int s3c2410_set_rtc(void)有以下说明，所以对2410，要求的时间应该是从2000以后。
yeardiff = (rtc_tm.tm_year + 1900) - RTC_LEAP_YEAR;
if (yeardiff < 0) {
/* S3C2410 RTC forces that the year must be higher or
equal than 2000, so initailize it. */
yeardiff = 0;
}
2.
s3c2410中的第四个timer用于作为系统的时间片
timer interrupt
在 setup_timer(void)函数中安装，
timer_irq.handler = s3c2410_timer_interrupt;//timer_irq定义在/*linux/arch/arm/kernel/time.c*/
setup_arm_irq(IRQ_TIMER4, &timer_irq);
TCON = (TCON_4_AUTO | COUNT_4_ON);//开始计数
timer_interrupt()调用do_timer()完成时钟中断上半部分处理；如果需要（可查看do_set_rtc()代码），还要刷新rtc中的信息，以便rtc和os时钟同步sync.RTC的更新频率是每11分钟刷新一次。
static void s3c2410_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
long flags;
do_leds(); //linux/arch/arm/kernel/time.c
根据系统中的xtime.tv_sec，更新rtc时钟。
调用了decodetime把1970年来的second值转换为Gre时间(from 1900)，并转化为BCD码，写入时钟芯片.函数仅返回0，无任何错误返回..用于sync update CMOS clock accordingly every ~11 minutes
do_set_rtc(); //linux/arch/arm/kernel/time.c,
save_flags_cli(flags);
do_timer(regs);
restore_flags(flags);
}
在include/linux/rtc.h中重要函数和常量定义
Generic RTC interface
/*
* The struct used to pass data via the following ioctl. Similar to the
* struct tm in , but it needs to be here so that the kernel
* source is self contained, allowing cross-compiles, etc. etc.
*/
struct rtc_time {
int tm_sec;
int tm_min;
int tm_hour;
int tm_mday;
int tm_mon;
int tm_year;
int tm_wday;
int tm_yday;
int tm_isdst;
};
关于时钟的系统调用： linux/kernel/time.c
sys_time:获得系统时间；
sys_stime:设置系统时间；
sys_gettimeofday:获得系统时间和时区；
sys_settimeofday:设置系统时间和时区；
sys_adjtimex:调整整个计时系统。
* This file contains the interface functions for the various
* time related system calls: time, stime, gettimeofday, settimeofday,adjtime
asmlinkage long sys_time(int * tloc)
asmlinkage long sys_stime(int * tptr)
asmlinkage long sys_gettimeofday(struct timeval *tv, struct timezone *tz)
asmlinkage long sys_settimeofday(struct timeval *tv, struct timezone *tz)
asmlinkage long sys_adjtimex(struct timex *txc_p)这个的实现比较长，没看懂
-------------------------------------------------
asmlinkage long sys_time(int * tloc)返回秒值
{
struct timeval now;
int i;
do_gettimeofday(&now);
i = now.tv_sec;
if (tloc) {
if (put_user(i,tloc))
i = -EFAULT;
}
return i;
}
asmlinkage long sys_stime(int * tptr)
{
int value;
if (!capable(CAP_SYS_TIME))
return -EPERM;
if (get_user(value, tptr))
return -EFAULT;
write_lock_irq(&xtime_lock);
xtime.tv_sec = value;
xtime.tv_usec = 0;
time_adjust = 0; /* stop active adjtime() */
time_status |= STA_UNSYNC;
time_maxerror = NTP_PHASE_LIMIT;
time_esterror = NTP_PHASE_LIMIT;
write_unlock_irq(&xtime_lock);
return 0;
}
asmlinkage long sys_gettimeofday(struct timeval *tv, struct timezone *tz)
{
if (tv) {
struct timeval ktv;
do_gettimeofday(&ktv);
if (copy_to_user(tv, &ktv, sizeof(ktv)))
return -EFAULT;
}
if (tz) {
if (copy_to_user(tz, &sys_tz, sizeof(sys_tz)))
return -EFAULT;
}
return 0;
}
int do_sys_settimeofday(struct timeval *tv, struct timezone *tz)
{
static int firsttime = 1;
if (!capable(CAP_SYS_TIME))
return -EPERM;
if (tz) {
/* SMP safe, global irq locking makes it work. */
sys_tz = *tz;
if (firsttime) {
firsttime = 0;
if (!tv)
warp_clock();
}
}
if (tv)
{
/* SMP safe, again the code in arch/foo/time.c should
* globally block out interrupts when it runs.
*/
do_settimeofday(tv);
}
return 0;
}
asmlinkage long sys_settimeofday(struct timeval *tv, struct timezone *tz)
{
struct timeval new_tv;
struct timezone new_tz;
if (tv) {
if (copy_from_user(&new_tv, tv, sizeof(*tv)))
return -EFAULT;
}
if (tz) {
if (copy_from_user(&new_tz, tz, sizeof(*tz)))
return -EFAULT;
}
return do_sys_settimeofday(tv ? &new_tv : NULL, tz ? &new_tz : NULL);
}
