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| -rw-r--r-- | Documentation/rtc.txt | 463 |
1 files changed, 304 insertions, 159 deletions
diff --git a/Documentation/rtc.txt b/Documentation/rtc.txt index 2a58f98..7cf1ec5 100644 --- a/Documentation/rtc.txt +++ b/Documentation/rtc.txt @@ -1,12 +1,49 @@ - Real Time Clock Driver for Linux - ================================ + Real Time Clock (RTC) Drivers for Linux + ======================================= + +When Linux developers talk about a "Real Time Clock", they usually mean +something that tracks wall clock time and is battery backed so that it +works even with system power off. Such clocks will normally not track +the local time zone or daylight savings time -- unless they dual boot +with MS-Windows -- but will instead be set to Coordinated Universal Time +(UTC, formerly "Greenwich Mean Time"). + +The newest non-PC hardware tends to just count seconds, like the time(2) +system call reports, but RTCs also very commonly represent time using +the Gregorian calendar and 24 hour time, as reported by gmtime(3). + +Linux has two largely-compatible userspace RTC API families you may +need to know about: + + * /dev/rtc ... is the RTC provided by PC compatible systems, + so it's not very portable to non-x86 systems. + + * /dev/rtc0, /dev/rtc1 ... are part of a framework that's + supported by a wide variety of RTC chips on all systems. + +Programmers need to understand that the PC/AT functionality is not +always available, and some systems can do much more. That is, the +RTCs use the same API to make requests in both RTC frameworks (using +different filenames of course), but the hardware may not offer the +same functionality. For example, not every RTC is hooked up to an +IRQ, so they can't all issue alarms; and where standard PC RTCs can +only issue an alarm up to 24 hours in the future, other hardware may +be able to schedule one any time in the upcoming century. + + + Old PC/AT-Compatible driver: /dev/rtc + -------------------------------------- All PCs (even Alpha machines) have a Real Time Clock built into them. Usually they are built into the chipset of the computer, but some may actually have a Motorola MC146818 (or clone) on the board. This is the clock that keeps the date and time while your computer is turned off. +ACPI has standardized that MC146818 functionality, and extended it in +a few ways (enabling longer alarm periods, and wake-from-hibernate). +That functionality is NOT exposed in the old driver. + However it can also be used to generate signals from a slow 2Hz to a relatively fast 8192Hz, in increments of powers of two. These signals are reported by interrupt number 8. (Oh! So *that* is what IRQ 8 is @@ -63,223 +100,331 @@ Rather than write 50 pages describing the ioctl() and so on, it is perhaps more useful to include a small test program that demonstrates how to use them, and demonstrates the features of the driver. This is probably a lot more useful to people interested in writing applications -that will be using this driver. +that will be using this driver. See the code at the end of this document. + +(The original /dev/rtc driver was written by Paul Gortmaker.) + + + New portable "RTC Class" drivers: /dev/rtcN + -------------------------------------------- + +Because Linux supports many non-ACPI and non-PC platforms, some of which +have more than one RTC style clock, it needed a more portable solution +than expecting a single battery-backed MC146818 clone on every system. +Accordingly, a new "RTC Class" framework has been defined. It offers +three different userspace interfaces: + + * /dev/rtcN ... much the same as the older /dev/rtc interface + + * /sys/class/rtc/rtcN ... sysfs attributes support readonly + access to some RTC attributes. + + * /proc/driver/rtc ... the first RTC (rtc0) may expose itself + using a procfs interface. More information is (currently) shown + here than through sysfs. + +The RTC Class framework supports a wide variety of RTCs, ranging from those +integrated into embeddable system-on-chip (SOC) processors to discrete chips +using I2C, SPI, or some other bus to communicate with the host CPU. There's +even support for PC-style RTCs ... including the features exposed on newer PCs +through ACPI. + +The new framework also removes the "one RTC per system" restriction. For +example, maybe the low-power battery-backed RTC is a discrete I2C chip, but +a high functionality RTC is integrated into the SOC. That system might read +the system clock from the discrete RTC, but use the integrated one for all +other tasks, because of its greater functionality. + +The ioctl() calls supported by /dev/rtc are also supported by the RTC class +framework. However, because the chips and systems are not standardized, +some PC/AT functionality might not be provided. And in the same way, some +newer features -- including those enabled by ACPI -- are exposed by the +RTC class framework, but can't be supported by the older driver. + + * RTC_RD_TIME, RTC_SET_TIME ... every RTC supports at least reading + time, returning the result as a Gregorian calendar date and 24 hour + wall clock time. To be most useful, this time may also be updated. + + * RTC_AIE_ON, RTC_AIE_OFF, RTC_ALM_SET, RTC_ALM_READ ... when the RTC + is connected to an IRQ line, it can often issue an alarm IRQ up to + 24 hours in the future. + + * RTC_WKALM_SET, RTC_WKALM_READ ... RTCs that can issue alarms beyond + the next 24 hours use a slightly more powerful API, which supports + setting the longer alarm time and enabling its IRQ using a single + request (using the same model as EFI firmware). + + * RTC_UIE_ON, RTC_UIE_OFF ... if the RTC offers IRQs, it probably + also offers update IRQs whenever the "seconds" counter changes. + If needed, the RTC framework can emulate this mechanism. + + * RTC_PIE_ON, RTC_PIE_OFF, RTC_IRQP_SET, RTC_IRQP_READ ... another + feature often accessible with an IRQ line is a periodic IRQ, issued + at settable frequencies (usually 2^N Hz). + +In many cases, the RTC alarm can be a system wake event, used to force +Linux out of a low power sleep state (or hibernation) back to a fully +operational state. For example, a system could enter a deep power saving +state until it's time to execute some scheduled tasks. - Paul Gortmaker -------------------- 8< ---------------- 8< ----------------------------- /* - * Real Time Clock Driver Test/Example Program + * Real Time Clock Driver Test/Example Program * - * Compile with: - * gcc -s -Wall -Wstrict-prototypes rtctest.c -o rtctest + * Compile with: + * gcc -s -Wall -Wstrict-prototypes rtctest.c -o rtctest * - * Copyright (C) 1996, Paul Gortmaker. + * Copyright (C) 1996, Paul Gortmaker. * - * Released under the GNU General Public License, version 2, - * included herein by reference. + * Released under the GNU General Public License, version 2, + * included herein by reference. * */ #include <stdio.h> -#include <stdlib.h> #include <linux/rtc.h> #include <sys/ioctl.h> #include <sys/time.h> #include <sys/types.h> #include <fcntl.h> #include <unistd.h> +#include <stdlib.h> #include <errno.h> -int main(void) { - -int i, fd, retval, irqcount = 0; -unsigned long tmp, data; -struct rtc_time rtc_tm; -fd = open ("/dev/rtc", O_RDONLY); +/* + * This expects the new RTC class driver framework, working with + * clocks that will often not be clones of what the PC-AT had. + * Use the command line to specify another RTC if you need one. + */ +static const char default_rtc[] = "/dev/rtc0"; + + +int main(int argc, char **argv) +{ + int i, fd, retval, irqcount = 0; + unsigned long tmp, data; + struct rtc_time rtc_tm; + const char *rtc = default_rtc; + + switch (argc) { + case 2: + rtc = argv[1]; + /* FALLTHROUGH */ + case 1: + break; + default: + fprintf(stderr, "usage: rtctest [rtcdev]\n"); + return 1; + } -if (fd == -1) { - perror("/dev/rtc"); - exit(errno); -} + fd = open(rtc, O_RDONLY); -fprintf(stderr, "\n\t\t\tRTC Driver Test Example.\n\n"); + if (fd == -1) { + perror(rtc); + exit(errno); + } -/* Turn on update interrupts (one per second) */ -retval = ioctl(fd, RTC_UIE_ON, 0); -if (retval == -1) { - perror("ioctl"); - exit(errno); -} + fprintf(stderr, "\n\t\t\tRTC Driver Test Example.\n\n"); -fprintf(stderr, "Counting 5 update (1/sec) interrupts from reading /dev/rtc:"); -fflush(stderr); -for (i=1; i<6; i++) { - /* This read will block */ - retval = read(fd, &data, sizeof(unsigned long)); + /* Turn on update interrupts (one per second) */ + retval = ioctl(fd, RTC_UIE_ON, 0); if (retval == -1) { - perror("read"); + if (errno == ENOTTY) { + fprintf(stderr, + "\n...Update IRQs not supported.\n"); + goto test_READ; + } + perror("ioctl"); exit(errno); } - fprintf(stderr, " %d",i); + + fprintf(stderr, "Counting 5 update (1/sec) interrupts from reading %s:", + rtc); fflush(stderr); - irqcount++; -} + for (i=1; i<6; i++) { + /* This read will block */ + retval = read(fd, &data, sizeof(unsigned long)); + if (retval == -1) { + perror("read"); + exit(errno); + } + fprintf(stderr, " %d",i); + fflush(stderr); + irqcount++; + } -fprintf(stderr, "\nAgain, from using select(2) on /dev/rtc:"); -fflush(stderr); -for (i=1; i<6; i++) { - struct timeval tv = {5, 0}; /* 5 second timeout on select */ - fd_set readfds; + fprintf(stderr, "\nAgain, from using select(2) on /dev/rtc:"); + fflush(stderr); + for (i=1; i<6; i++) { + struct timeval tv = {5, 0}; /* 5 second timeout on select */ + fd_set readfds; + + FD_ZERO(&readfds); + FD_SET(fd, &readfds); + /* The select will wait until an RTC interrupt happens. */ + retval = select(fd+1, &readfds, NULL, NULL, &tv); + if (retval == -1) { + perror("select"); + exit(errno); + } + /* This read won't block unlike the select-less case above. */ + retval = read(fd, &data, sizeof(unsigned long)); + if (retval == -1) { + perror("read"); + exit(errno); + } + fprintf(stderr, " %d",i); + fflush(stderr); + irqcount++; + } - FD_ZERO(&readfds); - FD_SET(fd, &readfds); - /* The select will wait until an RTC interrupt happens. */ - retval = select(fd+1, &readfds, NULL, NULL, &tv); + /* Turn off update interrupts */ + retval = ioctl(fd, RTC_UIE_OFF, 0); if (retval == -1) { - perror("select"); + perror("ioctl"); exit(errno); } - /* This read won't block unlike the select-less case above. */ - retval = read(fd, &data, sizeof(unsigned long)); + +test_READ: + /* Read the RTC time/date */ + retval = ioctl(fd, RTC_RD_TIME, &rtc_tm); if (retval == -1) { - perror("read"); + perror("ioctl"); exit(errno); } - fprintf(stderr, " %d",i); - fflush(stderr); - irqcount++; -} - -/* Turn off update interrupts */ -retval = ioctl(fd, RTC_UIE_OFF, 0); -if (retval == -1) { - perror("ioctl"); - exit(errno); -} - -/* Read the RTC time/date */ -retval = ioctl(fd, RTC_RD_TIME, &rtc_tm); -if (retval == -1) { - perror("ioctl"); - exit(errno); -} - -fprintf(stderr, "\n\nCurrent RTC date/time is %d-%d-%d, %02d:%02d:%02d.\n", - rtc_tm.tm_mday, rtc_tm.tm_mon + 1, rtc_tm.tm_year + 1900, - rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec); - -/* Set the alarm to 5 sec in the future, and check for rollover */ -rtc_tm.tm_sec += 5; -if (rtc_tm.tm_sec >= 60) { - rtc_tm.tm_sec %= 60; - rtc_tm.tm_min++; -} -if (rtc_tm.tm_min == 60) { - rtc_tm.tm_min = 0; - rtc_tm.tm_hour++; -} -if (rtc_tm.tm_hour == 24) - rtc_tm.tm_hour = 0; - -retval = ioctl(fd, RTC_ALM_SET, &rtc_tm); -if (retval == -1) { - perror("ioctl"); - exit(errno); -} - -/* Read the current alarm settings */ -retval = ioctl(fd, RTC_ALM_READ, &rtc_tm); -if (retval == -1) { - perror("ioctl"); - exit(errno); -} - -fprintf(stderr, "Alarm time now set to %02d:%02d:%02d.\n", - rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec); -/* Enable alarm interrupts */ -retval = ioctl(fd, RTC_AIE_ON, 0); -if (retval == -1) { - perror("ioctl"); - exit(errno); -} + fprintf(stderr, "\n\nCurrent RTC date/time is %d-%d-%d, %02d:%02d:%02d.\n", + rtc_tm.tm_mday, rtc_tm.tm_mon + 1, rtc_tm.tm_year + 1900, + rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec); -fprintf(stderr, "Waiting 5 seconds for alarm..."); -fflush(stderr); -/* This blocks until the alarm ring causes an interrupt */ -retval = read(fd, &data, sizeof(unsigned long)); -if (retval == -1) { - perror("read"); - exit(errno); -} -irqcount++; -fprintf(stderr, " okay. Alarm rang.\n"); - -/* Disable alarm interrupts */ -retval = ioctl(fd, RTC_AIE_OFF, 0); -if (retval == -1) { - perror("ioctl"); - exit(errno); -} + /* Set the alarm to 5 sec in the future, and check for rollover */ + rtc_tm.tm_sec += 5; + if (rtc_tm.tm_sec >= 60) { + rtc_tm.tm_sec %= 60; + rtc_tm.tm_min++; + } + if (rtc_tm.tm_min == 60) { + rtc_tm.tm_min = 0; + rtc_tm.tm_hour++; + } + if (rtc_tm.tm_hour == 24) + rtc_tm.tm_hour = 0; -/* Read periodic IRQ rate */ -retval = ioctl(fd, RTC_IRQP_READ, &tmp); -if (retval == -1) { - perror("ioctl"); - exit(errno); -} -fprintf(stderr, "\nPeriodic IRQ rate was %ldHz.\n", tmp); + retval = ioctl(fd, RTC_ALM_SET, &rtc_tm); + if (retval == -1) { + if (errno == ENOTTY) { + fprintf(stderr, + "\n...Alarm IRQs not supported.\n"); + goto test_PIE; + } + perror("ioctl"); + exit(errno); + } -fprintf(stderr, "Counting 20 interrupts at:"); -fflush(stderr); + /* Read the current alarm settings */ + retval = ioctl(fd, RTC_ALM_READ, &rtc_tm); + if (retval == -1) { + perror("ioctl"); + exit(errno); + } -/* The frequencies 128Hz, 256Hz, ... 8192Hz are only allowed for root. */ -for (tmp=2; tmp<=64; tmp*=2) { + fprintf(stderr, "Alarm time now set to %02d:%02d:%02d.\n", + rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec); - retval = ioctl(fd, RTC_IRQP_SET, tmp); + /* Enable alarm interrupts */ + retval = ioctl(fd, RTC_AIE_ON, 0); if (retval == -1) { perror("ioctl"); exit(errno); } - fprintf(stderr, "\n%ldHz:\t", tmp); + fprintf(stderr, "Waiting 5 seconds for alarm..."); fflush(stderr); + /* This blocks until the alarm ring causes an interrupt */ + retval = read(fd, &data, sizeof(unsigned long)); + if (retval == -1) { + perror("read"); + exit(errno); + } + irqcount++; + fprintf(stderr, " okay. Alarm rang.\n"); - /* Enable periodic interrupts */ - retval = ioctl(fd, RTC_PIE_ON, 0); + /* Disable alarm interrupts */ + retval = ioctl(fd, RTC_AIE_OFF, 0); if (retval == -1) { perror("ioctl"); exit(errno); } - for (i=1; i<21; i++) { - /* This blocks */ - retval = read(fd, &data, sizeof(unsigned long)); +test_PIE: + /* Read periodic IRQ rate */ + retval = ioctl(fd, RTC_IRQP_READ, &tmp); + if (retval == -1) { + /* not all RTCs support periodic IRQs */ + if (errno == ENOTTY) { + fprintf(stderr, "\nNo periodic IRQ support\n"); + return 0; + } + perror("ioctl"); + exit(errno); + } + fprintf(stderr, "\nPeriodic IRQ rate is %ldHz.\n", tmp); + + fprintf(stderr, "Counting 20 interrupts at:"); + fflush(stderr); + + /* The frequencies 128Hz, 256Hz, ... 8192Hz are only allowed for root. */ + for (tmp=2; tmp<=64; tmp*=2) { + + retval = ioctl(fd, RTC_IRQP_SET, tmp); if (retval == -1) { - perror("read"); - exit(errno); + /* not all RTCs can change their periodic IRQ rate */ + if (errno == ENOTTY) { + fprintf(stderr, + "\n...Periodic IRQ rate is fixed\n"); + goto done; + } + perror("ioctl"); + exit(errno); } - fprintf(stderr, " %d",i); + + fprintf(stderr, "\n%ldHz:\t", tmp); fflush(stderr); - irqcount++; - } - /* Disable periodic interrupts */ - retval = ioctl(fd, RTC_PIE_OFF, 0); - if (retval == -1) { - perror("ioctl"); - exit(errno); + /* Enable periodic interrupts */ + retval = ioctl(fd, RTC_PIE_ON, 0); + if (retval == -1) { + perror("ioctl"); + exit(errno); + } + + for (i=1; i<21; i++) { + /* This blocks */ + retval = read(fd, &data, sizeof(unsigned long)); + if (retval == -1) { + perror("read"); + exit(errno); + } + fprintf(stderr, " %d",i); + fflush(stderr); + irqcount++; + } + + /* Disable periodic interrupts */ + retval = ioctl(fd, RTC_PIE_OFF, 0); + if (retval == -1) { + perror("ioctl"); + exit(errno); + } } -} -fprintf(stderr, "\n\n\t\t\t *** Test complete ***\n"); -fprintf(stderr, "\nTyping \"cat /proc/interrupts\" will show %d more events on IRQ 8.\n\n", - irqcount); +done: + fprintf(stderr, "\n\n\t\t\t *** Test complete ***\n"); -close(fd); -return 0; + close(fd); -} /* end main */ + return 0; +} |
