Alexander Gordeev | 46b402a | 2011-01-12 17:00:59 -0800 | [diff] [blame] | 1 | /* |
| 2 | * pps_gen_parport.c -- kernel parallel port PPS signal generator |
| 3 | * |
| 4 | * |
| 5 | * Copyright (C) 2009 Alexander Gordeev <lasaine@lvk.cs.msu.su> |
| 6 | * |
| 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. |
| 11 | * |
| 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. |
| 16 | * |
| 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. |
| 20 | */ |
| 21 | |
| 22 | |
| 23 | /* |
| 24 | * TODO: |
| 25 | * fix issues when realtime clock is adjusted in a leap |
| 26 | */ |
| 27 | |
| 28 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt |
| 29 | |
| 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> |
| 36 | |
| 37 | #define DRVDESC "parallel port PPS signal generator" |
| 38 | |
| 39 | #define SIGNAL 0 |
| 40 | #define NO_SIGNAL PARPORT_CONTROL_STROBE |
| 41 | |
| 42 | /* module parameters */ |
| 43 | |
| 44 | #define SEND_DELAY_MAX 100000 |
| 45 | |
| 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); |
| 50 | |
| 51 | |
| 52 | #define SAFETY_INTERVAL 3000 /* set the hrtimer earlier for safety (ns) */ |
| 53 | |
| 54 | /* internal per port structure */ |
| 55 | struct pps_generator_pp { |
| 56 | struct pardevice *pardev; /* parport device */ |
| 57 | struct hrtimer timer; |
| 58 | long port_write_time; /* calibrated port write time (ns) */ |
| 59 | }; |
| 60 | |
| 61 | static struct pps_generator_pp device = { |
| 62 | .pardev = NULL, |
| 63 | }; |
| 64 | |
| 65 | static int attached; |
| 66 | |
| 67 | /* calibrated time between a hrtimer event and the reaction */ |
| 68 | static long hrtimer_error = SAFETY_INTERVAL; |
| 69 | |
| 70 | /* the kernel hrtimer event */ |
| 71 | static enum hrtimer_restart hrtimer_event(struct hrtimer *timer) |
| 72 | { |
| 73 | struct timespec expire_time, ts1, ts2, ts3, dts; |
| 74 | struct pps_generator_pp *dev; |
| 75 | struct parport *port; |
| 76 | long lim, delta; |
| 77 | unsigned long flags; |
| 78 | |
Alexander Gordeev | 563558b | 2011-01-12 17:01:00 -0800 | [diff] [blame] | 79 | /* We have to disable interrupts here. The idea is to prevent |
| 80 | * other interrupts on the same processor to introduce random |
| 81 | * lags while polling the clock. getnstimeofday() takes <1us on |
| 82 | * most machines while other interrupt handlers can take much |
| 83 | * more potentially. |
| 84 | * |
| 85 | * NB: approx time with blocked interrupts = |
| 86 | * send_delay + 3 * SAFETY_INTERVAL |
| 87 | */ |
Alexander Gordeev | 46b402a | 2011-01-12 17:00:59 -0800 | [diff] [blame] | 88 | local_irq_save(flags); |
| 89 | |
| 90 | /* first of all we get the time stamp... */ |
| 91 | getnstimeofday(&ts1); |
| 92 | expire_time = ktime_to_timespec(hrtimer_get_softexpires(timer)); |
| 93 | dev = container_of(timer, struct pps_generator_pp, timer); |
| 94 | lim = NSEC_PER_SEC - send_delay - dev->port_write_time; |
| 95 | |
| 96 | /* check if we are late */ |
| 97 | if (expire_time.tv_sec != ts1.tv_sec || ts1.tv_nsec > lim) { |
| 98 | local_irq_restore(flags); |
| 99 | pr_err("we are late this time %ld.%09ld\n", |
| 100 | ts1.tv_sec, ts1.tv_nsec); |
| 101 | goto done; |
| 102 | } |
| 103 | |
| 104 | /* busy loop until the time is right for an assert edge */ |
| 105 | do { |
| 106 | getnstimeofday(&ts2); |
| 107 | } while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim); |
| 108 | |
| 109 | /* set the signal */ |
| 110 | port = dev->pardev->port; |
| 111 | port->ops->write_control(port, SIGNAL); |
| 112 | |
| 113 | /* busy loop until the time is right for a clear edge */ |
| 114 | lim = NSEC_PER_SEC - dev->port_write_time; |
| 115 | do { |
| 116 | getnstimeofday(&ts2); |
| 117 | } while (expire_time.tv_sec == ts2.tv_sec && ts2.tv_nsec < lim); |
| 118 | |
| 119 | /* unset the signal */ |
| 120 | port->ops->write_control(port, NO_SIGNAL); |
| 121 | |
| 122 | getnstimeofday(&ts3); |
| 123 | |
| 124 | local_irq_restore(flags); |
| 125 | |
| 126 | /* update calibrated port write time */ |
| 127 | dts = timespec_sub(ts3, ts2); |
| 128 | dev->port_write_time = |
| 129 | (dev->port_write_time + timespec_to_ns(&dts)) >> 1; |
| 130 | |
| 131 | done: |
| 132 | /* update calibrated hrtimer error */ |
| 133 | dts = timespec_sub(ts1, expire_time); |
| 134 | delta = timespec_to_ns(&dts); |
| 135 | /* If the new error value is bigger then the old, use the new |
| 136 | * value, if not then slowly move towards the new value. This |
| 137 | * way it should be safe in bad conditions and efficient in |
| 138 | * good conditions. |
| 139 | */ |
| 140 | if (delta >= hrtimer_error) |
| 141 | hrtimer_error = delta; |
| 142 | else |
| 143 | hrtimer_error = (3 * hrtimer_error + delta) >> 2; |
| 144 | |
| 145 | /* update the hrtimer expire time */ |
| 146 | hrtimer_set_expires(timer, |
| 147 | ktime_set(expire_time.tv_sec + 1, |
| 148 | NSEC_PER_SEC - (send_delay + |
| 149 | dev->port_write_time + SAFETY_INTERVAL + |
| 150 | 2 * hrtimer_error))); |
| 151 | |
| 152 | return HRTIMER_RESTART; |
| 153 | } |
| 154 | |
| 155 | /* calibrate port write time */ |
| 156 | #define PORT_NTESTS_SHIFT 5 |
| 157 | static void calibrate_port(struct pps_generator_pp *dev) |
| 158 | { |
| 159 | struct parport *port = dev->pardev->port; |
| 160 | int i; |
| 161 | long acc = 0; |
| 162 | |
| 163 | for (i = 0; i < (1 << PORT_NTESTS_SHIFT); i++) { |
| 164 | struct timespec a, b; |
| 165 | unsigned long irq_flags; |
| 166 | |
| 167 | local_irq_save(irq_flags); |
| 168 | getnstimeofday(&a); |
| 169 | port->ops->write_control(port, NO_SIGNAL); |
| 170 | getnstimeofday(&b); |
| 171 | local_irq_restore(irq_flags); |
| 172 | |
| 173 | b = timespec_sub(b, a); |
| 174 | acc += timespec_to_ns(&b); |
| 175 | } |
| 176 | |
| 177 | dev->port_write_time = acc >> PORT_NTESTS_SHIFT; |
| 178 | pr_info("port write takes %ldns\n", dev->port_write_time); |
| 179 | } |
| 180 | |
| 181 | static inline ktime_t next_intr_time(struct pps_generator_pp *dev) |
| 182 | { |
| 183 | struct timespec ts; |
| 184 | |
| 185 | getnstimeofday(&ts); |
| 186 | |
| 187 | return ktime_set(ts.tv_sec + |
| 188 | ((ts.tv_nsec > 990 * NSEC_PER_MSEC) ? 1 : 0), |
| 189 | NSEC_PER_SEC - (send_delay + |
| 190 | dev->port_write_time + 3 * SAFETY_INTERVAL)); |
| 191 | } |
| 192 | |
| 193 | static void parport_attach(struct parport *port) |
| 194 | { |
| 195 | if (attached) { |
| 196 | /* we already have a port */ |
| 197 | return; |
| 198 | } |
| 199 | |
| 200 | device.pardev = parport_register_device(port, KBUILD_MODNAME, |
Alexander Gordeev | 4f542e3 | 2011-01-25 15:07:19 -0800 | [diff] [blame] | 201 | NULL, NULL, NULL, PARPORT_FLAG_EXCL, &device); |
Alexander Gordeev | 46b402a | 2011-01-12 17:00:59 -0800 | [diff] [blame] | 202 | if (!device.pardev) { |
| 203 | pr_err("couldn't register with %s\n", port->name); |
| 204 | return; |
| 205 | } |
| 206 | |
| 207 | if (parport_claim_or_block(device.pardev) < 0) { |
| 208 | pr_err("couldn't claim %s\n", port->name); |
| 209 | goto err_unregister_dev; |
| 210 | } |
| 211 | |
| 212 | pr_info("attached to %s\n", port->name); |
| 213 | attached = 1; |
| 214 | |
| 215 | calibrate_port(&device); |
| 216 | |
| 217 | hrtimer_init(&device.timer, CLOCK_REALTIME, HRTIMER_MODE_ABS); |
| 218 | device.timer.function = hrtimer_event; |
Alexander Gordeev | 46b402a | 2011-01-12 17:00:59 -0800 | [diff] [blame] | 219 | hrtimer_start(&device.timer, next_intr_time(&device), HRTIMER_MODE_ABS); |
| 220 | |
| 221 | return; |
| 222 | |
| 223 | err_unregister_dev: |
| 224 | parport_unregister_device(device.pardev); |
| 225 | } |
| 226 | |
| 227 | static void parport_detach(struct parport *port) |
| 228 | { |
| 229 | if (port->cad != device.pardev) |
| 230 | return; /* not our port */ |
| 231 | |
| 232 | hrtimer_cancel(&device.timer); |
| 233 | parport_release(device.pardev); |
| 234 | parport_unregister_device(device.pardev); |
| 235 | } |
| 236 | |
| 237 | static struct parport_driver pps_gen_parport_driver = { |
| 238 | .name = KBUILD_MODNAME, |
| 239 | .attach = parport_attach, |
| 240 | .detach = parport_detach, |
| 241 | }; |
| 242 | |
| 243 | /* module staff */ |
| 244 | |
| 245 | static int __init pps_gen_parport_init(void) |
| 246 | { |
| 247 | int ret; |
| 248 | |
| 249 | pr_info(DRVDESC "\n"); |
| 250 | |
| 251 | if (send_delay > SEND_DELAY_MAX) { |
| 252 | pr_err("delay value should be not greater" |
| 253 | " then %d\n", SEND_DELAY_MAX); |
| 254 | return -EINVAL; |
| 255 | } |
| 256 | |
| 257 | ret = parport_register_driver(&pps_gen_parport_driver); |
| 258 | if (ret) { |
| 259 | pr_err("unable to register with parport\n"); |
| 260 | return ret; |
| 261 | } |
| 262 | |
| 263 | return 0; |
| 264 | } |
| 265 | |
| 266 | static void __exit pps_gen_parport_exit(void) |
| 267 | { |
| 268 | parport_unregister_driver(&pps_gen_parport_driver); |
| 269 | pr_info("hrtimer avg error is %ldns\n", hrtimer_error); |
| 270 | } |
| 271 | |
| 272 | module_init(pps_gen_parport_init); |
| 273 | module_exit(pps_gen_parport_exit); |
| 274 | |
| 275 | MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>"); |
| 276 | MODULE_DESCRIPTION(DRVDESC); |
| 277 | MODULE_LICENSE("GPL"); |