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    Subject[PATCHv2 5/6] pps: add parallel port PPS signal generator
    Date
    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.

    Signed-off-by: Alexander Gordeev <lasaine@lvk.cs.msu.su>
    ---
    drivers/pps/Kconfig | 2 +
    drivers/pps/Makefile | 1 +
    drivers/pps/generators/Kconfig | 17 ++
    drivers/pps/generators/Makefile | 9 +
    drivers/pps/generators/pps_gen_parport.c | 264 ++++++++++++++++++++++++++++++
    5 files changed, 293 insertions(+), 0 deletions(-)
    create mode 100644 drivers/pps/generators/Kconfig
    create mode 100644 drivers/pps/generators/Makefile
    create mode 100644 drivers/pps/generators/pps_gen_parport.c

    diff --git a/drivers/pps/Kconfig b/drivers/pps/Kconfig
    index 2bd4f65..f3b14cd 100644
    --- a/drivers/pps/Kconfig
    +++ b/drivers/pps/Kconfig
    @@ -31,4 +31,6 @@ config PPS_DEBUG
    messages to the system log. Select this if you are having a
    problem with PPS support and want to see more of what is going on.

    +source drivers/pps/generators/Kconfig
    +
    endmenu
    diff --git a/drivers/pps/Makefile b/drivers/pps/Makefile
    index 19ea582..b299814 100644
    --- a/drivers/pps/Makefile
    +++ b/drivers/pps/Makefile
    @@ -4,5 +4,6 @@

    pps_core-y := pps.o kapi.o sysfs.o
    obj-$(CONFIG_PPS) := pps_core.o
    +obj-y += generators/

    ccflags-$(CONFIG_PPS_DEBUG) := -DDEBUG
    diff --git a/drivers/pps/generators/Kconfig b/drivers/pps/generators/Kconfig
    new file mode 100644
    index 0000000..9cc1118
    --- /dev/null
    +++ b/drivers/pps/generators/Kconfig
    @@ -0,0 +1,17 @@
    +#
    +# PPS clients configuration
    +#
    +
    +if PPS
    +
    +comment "PPS generators support"
    +
    +config PPS_GENERATOR_PARPORT
    + tristate "Parallel port PPS signal generator"
    + depends on PARPORT != n && GENERIC_TIME
    + help
    + If you say yes here you get support for a PPS signal generator which
    + utilizes STROBE pin of a parallel port to send PPS signals. It uses
    + parport abstraction layer and hrtimers to precisely control the signal.
    +
    +endif
    diff --git a/drivers/pps/generators/Makefile b/drivers/pps/generators/Makefile
    new file mode 100644
    index 0000000..303304a
    --- /dev/null
    +++ b/drivers/pps/generators/Makefile
    @@ -0,0 +1,9 @@
    +#
    +# Makefile for PPS generators.
    +#
    +
    +obj-$(CONFIG_PPS_GENERATOR_PARPORT) += pps_gen_parport.o
    +
    +ifeq ($(CONFIG_PPS_DEBUG),y)
    +EXTRA_CFLAGS += -DDEBUG
    +endif
    diff --git a/drivers/pps/generators/pps_gen_parport.c b/drivers/pps/generators/pps_gen_parport.c
    new file mode 100644
    index 0000000..e7cce30
    --- /dev/null
    +++ b/drivers/pps/generators/pps_gen_parport.c
    @@ -0,0 +1,264 @@
    +/*
    + * 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:
    + * 1. module parameters
    + * 2. check that local interrupts are blocked in hrtimer handler
    + * 3. fix issues when realtime clock is adjusted in a leap
    + * 4. test under heavy load
    + */
    +
    +#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 DRVNAME "pps_gen_parport"
    +#define DRVDESC "parallel port PPS signal generator"
    +
    +#define SIGNAL 0
    +#define NO_SIGNAL PARPORT_CONTROL_STROBE
    +
    +#define SEND_DELAY 30000 /* delay between setting and
    + dropping the signal (ns) */
    +#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(timer->_expires);
    + 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(DRVNAME ": 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(DRVNAME ": 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, DRVNAME,
    + NULL, NULL, NULL, 0, &device);
    + if (!device.pardev) {
    + pr_err(DRVNAME ": couldn't register with %s\n", port->name);
    + return;
    + }
    +
    + if (parport_claim_or_block(device.pardev) < 0) {
    + pr_err(DRVNAME ": couldn't claim %s\n", port->name);
    + goto err_unregister_dev;
    + }
    +
    + pr_info(DRVNAME ": 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)
    + /* not our port */
    + return;
    +
    + hrtimer_cancel(&device.timer);
    + parport_release(device.pardev);
    + parport_unregister_device(device.pardev);
    +}
    +
    +static struct parport_driver pps_gen_parport_driver = {
    + .name = DRVNAME,
    + .attach = parport_attach,
    + .detach = parport_detach,
    +};
    +
    +/* module staff */
    +
    +static int __init pps_gen_parport_init(void)
    +{
    + int ret;
    +
    + pr_info(DRVNAME ": " DRVDESC "\n");
    +
    + ret = parport_register_driver(&pps_gen_parport_driver);
    + if (ret) {
    + pr_err(DRVNAME ": 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(DRVNAME ": 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");
    --
    1.6.6.1


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