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
Linus Torvalds
parent
a10203c691
commit
46b402a0e5
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@ -170,3 +170,49 @@ and the run ppstest as follow:
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Please, note that to compile userland programs you need the file timepps.h
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(see Documentation/pps/).
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Generators
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----------
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Sometimes one needs to be able not only to catch PPS signals but to produce
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them also. For example, running a distributed simulation, which requires
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computers' clock to be synchronized very tightly. One way to do this is to
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invent some complicated hardware solutions but it may be neither necessary
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nor affordable. The cheap way is to load a PPS generator on one of the
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computers (master) and PPS clients on others (slaves), and use very simple
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cables to deliver signals using parallel ports, for example.
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Parallel port cable pinout:
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pin name master slave
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1 STROBE *------ *
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2 D0 * | *
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3 D1 * | *
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4 D2 * | *
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5 D3 * | *
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6 D4 * | *
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7 D5 * | *
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8 D6 * | *
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9 D7 * | *
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10 ACK * ------*
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11 BUSY * *
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12 PE * *
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13 SEL * *
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14 AUTOFD * *
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15 ERROR * *
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16 INIT * *
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17 SELIN * *
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18-25 GND *-----------*
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Please note that parallel port interrupt occurs only on high->low transition,
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so it is used for PPS assert edge. PPS clear edge can be determined only
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using polling in the interrupt handler which actually can be done way more
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precisely because interrupt handling delays can be quite big and random. So
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current parport PPS generator implementation (pps_gen_parport module) is
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geared towards using the clear edge for time synchronization.
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Clear edge polling is done with disabled interrupts so it's better to select
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delay between assert and clear edge as small as possible to reduce system
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latencies. But if it is too small slave won't be able to capture clear edge
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transition. The default of 30us should be good enough in most situations.
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The delay can be selected using 'delay' pps_gen_parport module parameter.
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@ -41,4 +41,6 @@ config NTP_PPS
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source drivers/pps/clients/Kconfig
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source drivers/pps/generators/Kconfig
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endmenu
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@ -5,6 +5,6 @@
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pps_core-y := pps.o kapi.o sysfs.o
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pps_core-$(CONFIG_NTP_PPS) += kc.o
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obj-$(CONFIG_PPS) := pps_core.o
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obj-y += clients/
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obj-y += clients/ generators/
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ccflags-$(CONFIG_PPS_DEBUG) := -DDEBUG
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@ -0,0 +1,17 @@
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#
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# PPS generators configuration
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#
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if PPS
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comment "PPS generators support"
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config PPS_GENERATOR_PARPORT
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tristate "Parallel port PPS signal generator"
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depends on PARPORT != n && GENERIC_TIME
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help
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If you say yes here you get support for a PPS signal generator which
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utilizes STROBE pin of a parallel port to send PPS signals. It uses
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parport abstraction layer and hrtimers to precisely control the signal.
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endif
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@ -0,0 +1,9 @@
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#
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# Makefile for PPS generators.
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#
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obj-$(CONFIG_PPS_GENERATOR_PARPORT) += pps_gen_parport.o
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ifeq ($(CONFIG_PPS_DEBUG),y)
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EXTRA_CFLAGS += -DDEBUG
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endif
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@ -0,0 +1,275 @@
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/*
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* pps_gen_parport.c -- kernel parallel port PPS signal generator
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*
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*
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* Copyright (C) 2009 Alexander Gordeev <lasaine@lvk.cs.msu.su>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/*
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* TODO:
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* fix issues when realtime clock is adjusted in a leap
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/time.h>
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#include <linux/hrtimer.h>
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#include <linux/parport.h>
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#define DRVDESC "parallel port PPS signal generator"
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#define SIGNAL 0
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#define NO_SIGNAL PARPORT_CONTROL_STROBE
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/* module parameters */
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#define SEND_DELAY_MAX 100000
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static unsigned int send_delay = 30000;
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MODULE_PARM_DESC(delay,
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"Delay between setting and dropping the signal (ns)");
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module_param_named(delay, send_delay, uint, 0);
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#define SAFETY_INTERVAL 3000 /* set the hrtimer earlier for safety (ns) */
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/* internal per port structure */
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struct pps_generator_pp {
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struct pardevice *pardev; /* parport device */
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struct hrtimer timer;
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long port_write_time; /* calibrated port write time (ns) */
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};
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static struct pps_generator_pp device = {
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.pardev = NULL,
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};
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static int attached;
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/* calibrated time between a hrtimer event and the reaction */
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static long hrtimer_error = SAFETY_INTERVAL;
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/* the kernel hrtimer event */
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static enum hrtimer_restart hrtimer_event(struct hrtimer *timer)
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{
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struct timespec expire_time, ts1, ts2, ts3, dts;
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struct pps_generator_pp *dev;
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struct parport *port;
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long lim, delta;
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unsigned long flags;
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/* NB: approx time with blocked interrupts =
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send_delay + 3 * SAFETY_INTERVAL */
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local_irq_save(flags);
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/* first of all we get the time stamp... */
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getnstimeofday(&ts1);
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expire_time = ktime_to_timespec(hrtimer_get_softexpires(timer));
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dev = container_of(timer, struct pps_generator_pp, timer);
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lim = NSEC_PER_SEC - send_delay - dev->port_write_time;
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/* check if we are late */
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if (expire_time.tv_sec != ts1.tv_sec || ts1.tv_nsec > lim) {
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local_irq_restore(flags);
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pr_err("we are late this time %ld.%09ld\n",
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ts1.tv_sec, ts1.tv_nsec);
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goto done;
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}
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/* busy loop until the time is right for an assert edge */
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do {
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getnstimeofday(&ts2);
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} while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
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/* set the signal */
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port = dev->pardev->port;
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port->ops->write_control(port, SIGNAL);
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/* busy loop until the time is right for a clear edge */
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lim = NSEC_PER_SEC - dev->port_write_time;
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do {
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getnstimeofday(&ts2);
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} while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
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/* unset the signal */
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port->ops->write_control(port, NO_SIGNAL);
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getnstimeofday(&ts3);
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local_irq_restore(flags);
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/* update calibrated port write time */
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dts = timespec_sub(ts3, ts2);
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dev->port_write_time =
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(dev->port_write_time + timespec_to_ns(&dts)) >> 1;
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done:
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/* update calibrated hrtimer error */
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dts = timespec_sub(ts1, expire_time);
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delta = timespec_to_ns(&dts);
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/* If the new error value is bigger then the old, use the new
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* value, if not then slowly move towards the new value. This
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* way it should be safe in bad conditions and efficient in
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* good conditions.
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*/
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if (delta >= hrtimer_error)
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hrtimer_error = delta;
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else
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hrtimer_error = (3 * hrtimer_error + delta) >> 2;
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/* update the hrtimer expire time */
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hrtimer_set_expires(timer,
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ktime_set(expire_time.tv_sec + 1,
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NSEC_PER_SEC - (send_delay +
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dev->port_write_time + SAFETY_INTERVAL +
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2 * hrtimer_error)));
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return HRTIMER_RESTART;
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}
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/* calibrate port write time */
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#define PORT_NTESTS_SHIFT 5
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static void calibrate_port(struct pps_generator_pp *dev)
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{
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struct parport *port = dev->pardev->port;
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int i;
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long acc = 0;
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for (i = 0; i < (1 << PORT_NTESTS_SHIFT); i++) {
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struct timespec a, b;
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unsigned long irq_flags;
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local_irq_save(irq_flags);
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getnstimeofday(&a);
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port->ops->write_control(port, NO_SIGNAL);
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getnstimeofday(&b);
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local_irq_restore(irq_flags);
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b = timespec_sub(b, a);
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acc += timespec_to_ns(&b);
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}
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dev->port_write_time = acc >> PORT_NTESTS_SHIFT;
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pr_info("port write takes %ldns\n", dev->port_write_time);
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}
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static inline ktime_t next_intr_time(struct pps_generator_pp *dev)
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{
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struct timespec ts;
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getnstimeofday(&ts);
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return ktime_set(ts.tv_sec +
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((ts.tv_nsec > 990 * NSEC_PER_MSEC) ? 1 : 0),
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NSEC_PER_SEC - (send_delay +
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dev->port_write_time + 3 * SAFETY_INTERVAL));
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}
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static void parport_attach(struct parport *port)
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{
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if (attached) {
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/* we already have a port */
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return;
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}
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device.pardev = parport_register_device(port, KBUILD_MODNAME,
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NULL, NULL, NULL, 0, &device);
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if (!device.pardev) {
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pr_err("couldn't register with %s\n", port->name);
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return;
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}
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if (parport_claim_or_block(device.pardev) < 0) {
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pr_err("couldn't claim %s\n", port->name);
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goto err_unregister_dev;
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}
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pr_info("attached to %s\n", port->name);
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attached = 1;
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calibrate_port(&device);
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hrtimer_init(&device.timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
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device.timer.function = hrtimer_event;
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#ifdef CONFIG_PREEMPT_RT
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/* hrtimer interrupt will run in the interrupt context with this */
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device.timer.irqsafe = 1;
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#endif
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hrtimer_start(&device.timer, next_intr_time(&device), HRTIMER_MODE_ABS);
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return;
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err_unregister_dev:
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parport_unregister_device(device.pardev);
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}
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static void parport_detach(struct parport *port)
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{
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if (port->cad != device.pardev)
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return; /* not our port */
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hrtimer_cancel(&device.timer);
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parport_release(device.pardev);
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parport_unregister_device(device.pardev);
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}
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static struct parport_driver pps_gen_parport_driver = {
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.name = KBUILD_MODNAME,
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.attach = parport_attach,
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.detach = parport_detach,
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};
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/* module staff */
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static int __init pps_gen_parport_init(void)
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{
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int ret;
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pr_info(DRVDESC "\n");
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if (send_delay > SEND_DELAY_MAX) {
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pr_err("delay value should be not greater"
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" then %d\n", SEND_DELAY_MAX);
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return -EINVAL;
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}
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ret = parport_register_driver(&pps_gen_parport_driver);
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if (ret) {
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pr_err("unable to register with parport\n");
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return ret;
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}
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return 0;
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}
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static void __exit pps_gen_parport_exit(void)
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{
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parport_unregister_driver(&pps_gen_parport_driver);
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pr_info("hrtimer avg error is %ldns\n", hrtimer_error);
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}
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module_init(pps_gen_parport_init);
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module_exit(pps_gen_parport_exit);
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MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>");
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MODULE_DESCRIPTION(DRVDESC);
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MODULE_LICENSE("GPL");
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