2 * pps_gen_parport.c -- kernel parallel port PPS signal generator
5 * Copyright (C) 2009 Alexander Gordeev <lasaine@lvk.cs.msu.su>
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 2 of the License, or
10 * (at your option) any later version.
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, write to the Free Software
19 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
25 * fix issues when realtime clock is adjusted in a leap
28 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
30 #include <linux/kernel.h>
31 #include <linux/module.h>
32 #include <linux/init.h>
33 #include <linux/time.h>
34 #include <linux/hrtimer.h>
35 #include <linux/parport.h>
37 #define DRVDESC "parallel port PPS signal generator"
40 #define NO_SIGNAL PARPORT_CONTROL_STROBE
42 /* module parameters */
44 #define SEND_DELAY_MAX 100000
46 static unsigned int send_delay = 30000;
47 MODULE_PARM_DESC(delay,
48 "Delay between setting and dropping the signal (ns)");
49 module_param_named(delay, send_delay, uint, 0);
52 #define SAFETY_INTERVAL 3000 /* set the hrtimer earlier for safety (ns) */
54 /* internal per port structure */
55 struct pps_generator_pp {
56 struct pardevice *pardev; /* parport device */
58 long port_write_time; /* calibrated port write time (ns) */
61 static struct pps_generator_pp device = {
67 /* calibrated time between a hrtimer event and the reaction */
68 static long hrtimer_error = SAFETY_INTERVAL;
70 /* the kernel hrtimer event */
71 static enum hrtimer_restart hrtimer_event(struct hrtimer *timer)
73 struct timespec expire_time, ts1, ts2, ts3, dts;
74 struct pps_generator_pp *dev;
79 /* NB: approx time with blocked interrupts =
80 send_delay + 3 * SAFETY_INTERVAL */
81 local_irq_save(flags);
83 /* first of all we get the time stamp... */
85 expire_time = ktime_to_timespec(hrtimer_get_softexpires(timer));
86 dev = container_of(timer, struct pps_generator_pp, timer);
87 lim = NSEC_PER_SEC - send_delay - dev->port_write_time;
89 /* check if we are late */
90 if (expire_time.tv_sec != ts1.tv_sec || ts1.tv_nsec > lim) {
91 local_irq_restore(flags);
92 pr_err("we are late this time %ld.%09ld\n",
93 ts1.tv_sec, ts1.tv_nsec);
97 /* busy loop until the time is right for an assert edge */
100 } while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
103 port = dev->pardev->port;
104 port->ops->write_control(port, SIGNAL);
106 /* busy loop until the time is right for a clear edge */
107 lim = NSEC_PER_SEC - dev->port_write_time;
109 getnstimeofday(&ts2);
110 } while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim);
112 /* unset the signal */
113 port->ops->write_control(port, NO_SIGNAL);
115 getnstimeofday(&ts3);
117 local_irq_restore(flags);
119 /* update calibrated port write time */
120 dts = timespec_sub(ts3, ts2);
121 dev->port_write_time =
122 (dev->port_write_time + timespec_to_ns(&dts)) >> 1;
125 /* update calibrated hrtimer error */
126 dts = timespec_sub(ts1, expire_time);
127 delta = timespec_to_ns(&dts);
128 /* If the new error value is bigger then the old, use the new
129 * value, if not then slowly move towards the new value. This
130 * way it should be safe in bad conditions and efficient in
133 if (delta >= hrtimer_error)
134 hrtimer_error = delta;
136 hrtimer_error = (3 * hrtimer_error + delta) >> 2;
138 /* update the hrtimer expire time */
139 hrtimer_set_expires(timer,
140 ktime_set(expire_time.tv_sec + 1,
141 NSEC_PER_SEC - (send_delay +
142 dev->port_write_time + SAFETY_INTERVAL +
143 2 * hrtimer_error)));
145 return HRTIMER_RESTART;
148 /* calibrate port write time */
149 #define PORT_NTESTS_SHIFT 5
150 static void calibrate_port(struct pps_generator_pp *dev)
152 struct parport *port = dev->pardev->port;
156 for (i = 0; i < (1 << PORT_NTESTS_SHIFT); i++) {
157 struct timespec a, b;
158 unsigned long irq_flags;
160 local_irq_save(irq_flags);
162 port->ops->write_control(port, NO_SIGNAL);
164 local_irq_restore(irq_flags);
166 b = timespec_sub(b, a);
167 acc += timespec_to_ns(&b);
170 dev->port_write_time = acc >> PORT_NTESTS_SHIFT;
171 pr_info("port write takes %ldns\n", dev->port_write_time);
174 static inline ktime_t next_intr_time(struct pps_generator_pp *dev)
180 return ktime_set(ts.tv_sec +
181 ((ts.tv_nsec > 990 * NSEC_PER_MSEC) ? 1 : 0),
182 NSEC_PER_SEC - (send_delay +
183 dev->port_write_time + 3 * SAFETY_INTERVAL));
186 static void parport_attach(struct parport *port)
189 /* we already have a port */
193 device.pardev = parport_register_device(port, KBUILD_MODNAME,
194 NULL, NULL, NULL, 0, &device);
195 if (!device.pardev) {
196 pr_err("couldn't register with %s\n", port->name);
200 if (parport_claim_or_block(device.pardev) < 0) {
201 pr_err("couldn't claim %s\n", port->name);
202 goto err_unregister_dev;
205 pr_info("attached to %s\n", port->name);
208 calibrate_port(&device);
210 hrtimer_init(&device.timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
211 device.timer.function = hrtimer_event;
212 #ifdef CONFIG_PREEMPT_RT
213 /* hrtimer interrupt will run in the interrupt context with this */
214 device.timer.irqsafe = 1;
217 hrtimer_start(&device.timer, next_intr_time(&device), HRTIMER_MODE_ABS);
222 parport_unregister_device(device.pardev);
225 static void parport_detach(struct parport *port)
227 if (port->cad != device.pardev)
228 return; /* not our port */
230 hrtimer_cancel(&device.timer);
231 parport_release(device.pardev);
232 parport_unregister_device(device.pardev);
235 static struct parport_driver pps_gen_parport_driver = {
236 .name = KBUILD_MODNAME,
237 .attach = parport_attach,
238 .detach = parport_detach,
243 static int __init pps_gen_parport_init(void)
247 pr_info(DRVDESC "\n");
249 if (send_delay > SEND_DELAY_MAX) {
250 pr_err("delay value should be not greater"
251 " then %d\n", SEND_DELAY_MAX);
255 ret = parport_register_driver(&pps_gen_parport_driver);
257 pr_err("unable to register with parport\n");
264 static void __exit pps_gen_parport_exit(void)
266 parport_unregister_driver(&pps_gen_parport_driver);
267 pr_info("hrtimer avg error is %ldns\n", hrtimer_error);
270 module_init(pps_gen_parport_init);
271 module_exit(pps_gen_parport_exit);
273 MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>");
274 MODULE_DESCRIPTION(DRVDESC);
275 MODULE_LICENSE("GPL");