diff options
| -rw-r--r-- | Documentation/pps/pps.txt | 46 | ||||
| -rw-r--r-- | drivers/pps/Kconfig | 2 | ||||
| -rw-r--r-- | drivers/pps/Makefile | 2 | ||||
| -rw-r--r-- | drivers/pps/generators/Kconfig | 17 | ||||
| -rw-r--r-- | drivers/pps/generators/Makefile | 9 | ||||
| -rw-r--r-- | drivers/pps/generators/pps_gen_parport.c | 275 |
6 files changed, 350 insertions, 1 deletions
diff --git a/Documentation/pps/pps.txt b/Documentation/pps/pps.txt index 125f4ab48998..d35dcdd82ff6 100644 --- a/Documentation/pps/pps.txt +++ b/Documentation/pps/pps.txt @@ -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. diff --git a/drivers/pps/Kconfig b/drivers/pps/Kconfig index 0ad5ff38bfec..f0d3376b58ba 100644 --- a/drivers/pps/Kconfig +++ b/drivers/pps/Kconfig @@ -41,4 +41,6 @@ config NTP_PPS source drivers/pps/clients/Kconfig +source drivers/pps/generators/Kconfig + endmenu diff --git a/drivers/pps/Makefile b/drivers/pps/Makefile index 77c23457b739..4483eaadaddd 100644 --- a/drivers/pps/Makefile +++ b/drivers/pps/Makefile @@ -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-$(CONFIG_PPS_DEBUG) := -DDEBUG diff --git a/drivers/pps/generators/Kconfig b/drivers/pps/generators/Kconfig new file mode 100644 index 000000000000..5fbd6148c804 --- /dev/null +++ b/drivers/pps/generators/Kconfig @@ -0,0 +1,17 @@ +# +# PPS generators configuration +# + +if PPS + +comment "PPS generators support" + +config PPS_GENERATOR_PARPORT + tristate "Parallel port PPS signal generator" + depends on PARPORT != n && GENERIC_TIME + help + If you say yes here you get support for a PPS signal generator which + utilizes STROBE pin of a parallel port to send PPS signals. It uses + parport abstraction layer and hrtimers to precisely control the signal. + +endif diff --git a/drivers/pps/generators/Makefile b/drivers/pps/generators/Makefile new file mode 100644 index 000000000000..303304a6b8ec --- /dev/null +++ b/drivers/pps/generators/Makefile @@ -0,0 +1,9 @@ +# +# Makefile for PPS generators. +# + +obj-$(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 000000000000..a15fe25efd55 --- /dev/null +++ b/drivers/pps/generators/pps_gen_parport.c @@ -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"); |