pps: add parallel port PPS signal generator

Add PPS signal generator which utilizes STROBE pin of a parallel port to
send PPS signals.  It uses parport abstraction layer and hrtimers to
precisely control the signal.

[akpm@linux-foundation.org: fix build]
Signed-off-by: Alexander Gordeev <lasaine@lvk.cs.msu.su>
Acked-by: Rodolfo Giometti <giometti@linux.it>
Cc: john stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Alexander Gordeev 2011-01-12 17:00:59 -08:00 committed by Linus Torvalds
parent a10203c691
commit 46b402a0e5
6 changed files with 350 additions and 1 deletions

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@ -170,3 +170,49 @@ and the run ppstest as follow:
Please, note that to compile userland programs you need the file timepps.h
(see Documentation/pps/).
Generators
----------
Sometimes one needs to be able not only to catch PPS signals but to produce
them also. For example, running a distributed simulation, which requires
computers' clock to be synchronized very tightly. One way to do this is to
invent some complicated hardware solutions but it may be neither necessary
nor affordable. The cheap way is to load a PPS generator on one of the
computers (master) and PPS clients on others (slaves), and use very simple
cables to deliver signals using parallel ports, for example.
Parallel port cable pinout:
pin name master slave
1 STROBE *------ *
2 D0 * | *
3 D1 * | *
4 D2 * | *
5 D3 * | *
6 D4 * | *
7 D5 * | *
8 D6 * | *
9 D7 * | *
10 ACK * ------*
11 BUSY * *
12 PE * *
13 SEL * *
14 AUTOFD * *
15 ERROR * *
16 INIT * *
17 SELIN * *
18-25 GND *-----------*
Please note that parallel port interrupt occurs only on high->low transition,
so it is used for PPS assert edge. PPS clear edge can be determined only
using polling in the interrupt handler which actually can be done way more
precisely because interrupt handling delays can be quite big and random. So
current parport PPS generator implementation (pps_gen_parport module) is
geared towards using the clear edge for time synchronization.
Clear edge polling is done with disabled interrupts so it's better to select
delay between assert and clear edge as small as possible to reduce system
latencies. But if it is too small slave won't be able to capture clear edge
transition. The default of 30us should be good enough in most situations.
The delay can be selected using 'delay' pps_gen_parport module parameter.

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@ -41,4 +41,6 @@ config NTP_PPS
source drivers/pps/clients/Kconfig
source drivers/pps/generators/Kconfig
endmenu

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@ -5,6 +5,6 @@
pps_core-y := pps.o kapi.o sysfs.o
pps_core-$(CONFIG_NTP_PPS) += kc.o
obj-$(CONFIG_PPS) := pps_core.o
obj-y += clients/
obj-y += clients/ generators/
ccflags-$(CONFIG_PPS_DEBUG) := -DDEBUG

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@ -0,0 +1,17 @@
#
# PPS generators configuration
#
if PPS
comment "PPS generators support"
config PPS_GENERATOR_PARPORT
tristate "Parallel port PPS signal generator"
depends on PARPORT != n && GENERIC_TIME
help
If you say yes here you get support for a PPS signal generator which
utilizes STROBE pin of a parallel port to send PPS signals. It uses
parport abstraction layer and hrtimers to precisely control the signal.
endif

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@ -0,0 +1,9 @@
#
# Makefile for PPS generators.
#
obj-$(CONFIG_PPS_GENERATOR_PARPORT) += pps_gen_parport.o
ifeq ($(CONFIG_PPS_DEBUG),y)
EXTRA_CFLAGS += -DDEBUG
endif

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@ -0,0 +1,275 @@
/*
* pps_gen_parport.c -- kernel parallel port PPS signal generator
*
*
* Copyright (C) 2009 Alexander Gordeev <lasaine@lvk.cs.msu.su>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/*
* TODO:
* fix issues when realtime clock is adjusted in a leap
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/time.h>
#include <linux/hrtimer.h>
#include <linux/parport.h>
#define DRVDESC "parallel port PPS signal generator"
#define SIGNAL 0
#define NO_SIGNAL PARPORT_CONTROL_STROBE
/* module parameters */
#define SEND_DELAY_MAX 100000
static unsigned int send_delay = 30000;
MODULE_PARM_DESC(delay,
"Delay between setting and dropping the signal (ns)");
module_param_named(delay, send_delay, uint, 0);
#define SAFETY_INTERVAL 3000 /* set the hrtimer earlier for safety (ns) */
/* internal per port structure */
struct pps_generator_pp {
struct pardevice *pardev; /* parport device */
struct hrtimer timer;
long port_write_time; /* calibrated port write time (ns) */
};
static struct pps_generator_pp device = {
.pardev = NULL,
};
static int attached;
/* calibrated time between a hrtimer event and the reaction */
static long hrtimer_error = SAFETY_INTERVAL;
/* the kernel hrtimer event */
static enum hrtimer_restart hrtimer_event(struct hrtimer *timer)
{
struct timespec expire_time, ts1, ts2, ts3, dts;
struct pps_generator_pp *dev;
struct parport *port;
long lim, delta;
unsigned long flags;
/* NB: approx time with blocked interrupts =
send_delay + 3 * SAFETY_INTERVAL */
local_irq_save(flags);
/* first of all we get the time stamp... */
getnstimeofday(&ts1);
expire_time = ktime_to_timespec(hrtimer_get_softexpires(timer));
dev = container_of(timer, struct pps_generator_pp, timer);
lim = NSEC_PER_SEC - send_delay - dev->port_write_time;
/* check if we are late */
if (expire_time.tv_sec != ts1.tv_sec || ts1.tv_nsec > lim) {
local_irq_restore(flags);
pr_err("we are late this time %ld.%09ld\n",
ts1.tv_sec, ts1.tv_nsec);
goto done;
}
/* busy loop until the time is right for an assert edge */
do {
getnstimeofday(&ts2);
} while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
/* set the signal */
port = dev->pardev->port;
port->ops->write_control(port, SIGNAL);
/* busy loop until the time is right for a clear edge */
lim = NSEC_PER_SEC - dev->port_write_time;
do {
getnstimeofday(&ts2);
} while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
/* unset the signal */
port->ops->write_control(port, NO_SIGNAL);
getnstimeofday(&ts3);
local_irq_restore(flags);
/* update calibrated port write time */
dts = timespec_sub(ts3, ts2);
dev->port_write_time =
(dev->port_write_time + timespec_to_ns(&dts)) >> 1;
done:
/* update calibrated hrtimer error */
dts = timespec_sub(ts1, expire_time);
delta = timespec_to_ns(&dts);
/* If the new error value is bigger then the old, use the new
* value, if not then slowly move towards the new value. This
* way it should be safe in bad conditions and efficient in
* good conditions.
*/
if (delta >= hrtimer_error)
hrtimer_error = delta;
else
hrtimer_error = (3 * hrtimer_error + delta) >> 2;
/* update the hrtimer expire time */
hrtimer_set_expires(timer,
ktime_set(expire_time.tv_sec + 1,
NSEC_PER_SEC - (send_delay +
dev->port_write_time + SAFETY_INTERVAL +
2 * hrtimer_error)));
return HRTIMER_RESTART;
}
/* calibrate port write time */
#define PORT_NTESTS_SHIFT 5
static void calibrate_port(struct pps_generator_pp *dev)
{
struct parport *port = dev->pardev->port;
int i;
long acc = 0;
for (i = 0; i < (1 << PORT_NTESTS_SHIFT); i++) {
struct timespec a, b;
unsigned long irq_flags;
local_irq_save(irq_flags);
getnstimeofday(&a);
port->ops->write_control(port, NO_SIGNAL);
getnstimeofday(&b);
local_irq_restore(irq_flags);
b = timespec_sub(b, a);
acc += timespec_to_ns(&b);
}
dev->port_write_time = acc >> PORT_NTESTS_SHIFT;
pr_info("port write takes %ldns\n", dev->port_write_time);
}
static inline ktime_t next_intr_time(struct pps_generator_pp *dev)
{
struct timespec ts;
getnstimeofday(&ts);
return ktime_set(ts.tv_sec +
((ts.tv_nsec > 990 * NSEC_PER_MSEC) ? 1 : 0),
NSEC_PER_SEC - (send_delay +
dev->port_write_time + 3 * SAFETY_INTERVAL));
}
static void parport_attach(struct parport *port)
{
if (attached) {
/* we already have a port */
return;
}
device.pardev = parport_register_device(port, KBUILD_MODNAME,
NULL, NULL, NULL, 0, &device);
if (!device.pardev) {
pr_err("couldn't register with %s\n", port->name);
return;
}
if (parport_claim_or_block(device.pardev) < 0) {
pr_err("couldn't claim %s\n", port->name);
goto err_unregister_dev;
}
pr_info("attached to %s\n", port->name);
attached = 1;
calibrate_port(&device);
hrtimer_init(&device.timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
device.timer.function = hrtimer_event;
#ifdef CONFIG_PREEMPT_RT
/* hrtimer interrupt will run in the interrupt context with this */
device.timer.irqsafe = 1;
#endif
hrtimer_start(&device.timer, next_intr_time(&device), HRTIMER_MODE_ABS);
return;
err_unregister_dev:
parport_unregister_device(device.pardev);
}
static void parport_detach(struct parport *port)
{
if (port->cad != device.pardev)
return; /* not our port */
hrtimer_cancel(&device.timer);
parport_release(device.pardev);
parport_unregister_device(device.pardev);
}
static struct parport_driver pps_gen_parport_driver = {
.name = KBUILD_MODNAME,
.attach = parport_attach,
.detach = parport_detach,
};
/* module staff */
static int __init pps_gen_parport_init(void)
{
int ret;
pr_info(DRVDESC "\n");
if (send_delay > SEND_DELAY_MAX) {
pr_err("delay value should be not greater"
" then %d\n", SEND_DELAY_MAX);
return -EINVAL;
}
ret = parport_register_driver(&pps_gen_parport_driver);
if (ret) {
pr_err("unable to register with parport\n");
return ret;
}
return 0;
}
static void __exit pps_gen_parport_exit(void)
{
parport_unregister_driver(&pps_gen_parport_driver);
pr_info("hrtimer avg error is %ldns\n", hrtimer_error);
}
module_init(pps_gen_parport_init);
module_exit(pps_gen_parport_exit);
MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>");
MODULE_DESCRIPTION(DRVDESC);
MODULE_LICENSE("GPL");