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Commit 7531d8fa authored by David Brownell's avatar David Brownell Committed by Linus Torvalds
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[PATCH] Documentation/rtc.txt updates (for rtc class) 

This updates the RTC documentation to summarize the two APIs now available:
the old PC/AT one, and the new RTC class drivers.  It also updates the
included "rtctest.c" file to better meet Linux style guidelines, and to work
with the new RTC drivers.
Signed-off-by: default avatarDavid Brownell <dbrownell@users.sourceforge.net>
Acked-by: default avatarAlessandro Zummo <a.zummo@towertech.it>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 4d8ebddc
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Documentation/rtc.txt
View file @ 7531d8fa
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
......@@ -63,9 +100,73 @@ 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< -----------------------------
......@@ -83,40 +184,67 @@ that will be using this driver.
*/
#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;
/*
* 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;
}
fd = open ("/dev/rtc", O_RDONLY);
fd = open(rtc, O_RDONLY);
if (fd == -1) {
perror("/dev/rtc");
if (fd == -1) {
perror(rtc);
exit(errno);
}
}
fprintf(stderr, "\n\t\t\tRTC Driver Test Example.\n\n");
fprintf(stderr, "\n\t\t\tRTC Driver Test Example.\n\n");
/* Turn on update interrupts (one per second) */
retval = ioctl(fd, RTC_UIE_ON, 0);
if (retval == -1) {
/* Turn on update interrupts (one per second) */
retval = ioctl(fd, RTC_UIE_ON, 0);
if (retval == -1) {
if (errno == ENOTTY) {
fprintf(stderr,
"\n...Update IRQs not supported.\n");
goto test_READ;
}
perror("ioctl");
exit(errno);
}
}
fprintf(stderr, "Counting 5 update (1/sec) interrupts from reading /dev/rtc:");
fflush(stderr);
for (i=1; i<6; i++) {
fprintf(stderr, "Counting 5 update (1/sec) interrupts from reading %s:",
rtc);
fflush(stderr);
for (i=1; i<6; i++) {
/* This read will block */
retval = read(fd, &data, sizeof(unsigned long));
if (retval == -1) {
......@@ -126,11 +254,11 @@ for (i=1; i<6; i++) {
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++) {
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;
......@@ -151,96 +279,114 @@ for (i=1; i<6; i++) {
fprintf(stderr, " %d",i);
fflush(stderr);
irqcount++;
}
}
/* Turn off update interrupts */
retval = ioctl(fd, RTC_UIE_OFF, 0);
if (retval == -1) {
/* 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) {
test_READ:
/* 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",
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) {
/* 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) {
}
if (rtc_tm.tm_min == 60) {
rtc_tm.tm_min = 0;
rtc_tm.tm_hour++;
}
if (rtc_tm.tm_hour == 24)
}
if (rtc_tm.tm_hour == 24)
rtc_tm.tm_hour = 0;
retval = ioctl(fd, RTC_ALM_SET, &rtc_tm);
if (retval == -1) {
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);
}
}
/* Read the current alarm settings */
retval = ioctl(fd, RTC_ALM_READ, &rtc_tm);
if (retval == -1) {
/* 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",
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) {
/* Enable alarm interrupts */
retval = ioctl(fd, RTC_AIE_ON, 0);
if (retval == -1) {
perror("ioctl");
exit(errno);
}
}
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) {
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");
}
irqcount++;
fprintf(stderr, " okay. Alarm rang.\n");
/* Disable alarm interrupts */
retval = ioctl(fd, RTC_AIE_OFF, 0);
if (retval == -1) {
/* Disable alarm interrupts */
retval = ioctl(fd, RTC_AIE_OFF, 0);
if (retval == -1) {
perror("ioctl");
exit(errno);
}
}
/* Read periodic IRQ rate */
retval = ioctl(fd, RTC_IRQP_READ, &tmp);
if (retval == -1) {
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 was %ldHz.\n", tmp);
}
fprintf(stderr, "\nPeriodic IRQ rate is %ldHz.\n", tmp);
fprintf(stderr, "Counting 20 interrupts at:");
fflush(stderr);
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) {
/* 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) {
/* 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);
}
......@@ -273,13 +419,12 @@ for (tmp=2; tmp<=64; tmp*=2) {
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;
}
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