1 /* $Id: pbms.c,v 1.3 2006/02/06 20:13:25 jmmv Exp $ */ 2 3 /* 4 * Copyright (c) 2005, Johan Wall�n 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions are 9 * met: 10 * 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 14 * 2. Redistributions in binary form must reproduce the above 15 * copyright notice, this list of conditions and the following 16 * disclaimer in the documentation and/or other materials provided 17 * with the distribution. 18 * 19 * 3. The name of the copyright holder may not be used to endorse or 20 * promote products derived from this software without specific 21 * prior written permission. 22 * 23 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER "AS IS" AND ANY 24 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 26 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER BE 27 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 28 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 29 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR 30 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 31 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 32 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 33 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 34 */ 35 36 /* 37 * The pbms driver provides support for the trackpad on new (post 38 * February 2005) Apple PowerBooks (and iBooks?) that are not standard 39 * USB HID mice. 40 */ 41 42 /* 43 * The protocol (that is, the interpretation of the data generated by 44 * the trackpad) is taken from the Linux appletouch driver version 45 * 0.08 by Johannes Berg, Stelian Pop and Frank Arnold. The method 46 * used to detect fingers on the trackpad is also taken from that 47 * driver. 48 */ 49 50 /* 51 * To add support for other devices using the same protocol, add an 52 * entry to the pbms_devices table below. See the comments for 53 * pbms_devices and struct pbms_devs. 54 */ 55 56 /* 57 * PROTOCOL: 58 * 59 * The driver transfers continuously 81 byte events. The last byte is 60 * 1 if the button is pressed, and is 0 otherwise. Of the remaining 61 * bytes, 26 + 16 = 42 are sensors detecting pressure in the X or 62 * horizontal, and Y or vertical directions, respectively. On 12 and 63 * 15 inch PowerBooks, only the 16 first sensors in the X-direction 64 * are used. In the X-direction, the sensors correspond to byte 65 * positions 66 * 67 * 2, 7, 12, 17, 22, 27, 32, 37, 4, 9, 14, 19, 24, 29, 34, 39, 42, 68 * 47, 52, 57, 62, 67, 72, 77, 44 and 49; 69 * 70 * in the Y direction, the sensors correspond to byte positions 71 * 72 * 1, 6, 11, 16, 21, 26, 31, 36, 3, 8, 13, 18, 23, 28, 33 and 38. 73 * 74 * The change in the sensor values over time is more interesting than 75 * their absolute values: if the pressure increases, we know that the 76 * finger has just moved there. 77 * 78 * We keep track of the previous sample (of sensor values in the X and 79 * Y directions) and the accumulated change for each sensor. When we 80 * receive a new sample, we add the difference of the new sensor value 81 * and the old value to the accumulated change. If the accumulator 82 * becomes negative, we set it to zero. The effect is that the 83 * accumulator is large for sensors whose pressure has recently 84 * increased. If there is little change in pressure (or if the 85 * pressure decreases), the accumulator drifts back to zero. 86 * 87 * Since there is some fluctuations, we ignore accumulator values 88 * below a threshold. The raw finger position is computed as a 89 * weighted average of the other sensors (the weights are the 90 * accumulated changes). 91 * 92 * For smoothing, we keep track of the previous raw finger position, 93 * and the virtual position reported to wsmouse. The new raw position 94 * is computed as a weighted average of the old raw position and the 95 * computed raw position. Since this still generates some noise, we 96 * compute a new virtual position as a weighted average of the previous 97 * virtual position and the new raw position. The weights are 98 * controlled by the raw change and a noise parameter. The position 99 * is reported as a relative position. 100 */ 101 102 /* 103 * TODO: 104 * 105 * Add support for other drivers of the same type. 106 * 107 * Add support for tapping and two-finger scrolling? The 108 * implementation already detects two fingers, so this should be 109 * relatively easy. 110 * 111 * Implement some of the mouse ioctls? 112 * 113 * Take care of the XXXs. 114 * 115 */ 116 117 #include <sys/cdefs.h> 118 119 #include <sys/param.h> 120 #include <sys/device.h> 121 #include <sys/errno.h> 122 123 #include <sys/ioctl.h> 124 #include <sys/systm.h> 125 #include <sys/tty.h> 126 127 #include <dev/usb/usb.h> 128 #include <dev/usb/usbdi.h> 129 #include <dev/usb/usbdevs.h> 130 #include <dev/usb/uhidev.h> 131 132 #include <dev/wscons/wsconsio.h> 133 #include <dev/wscons/wsmousevar.h> 134 135 136 /* 137 * Debugging output. 138 */ 139 140 141 /* XXX Should be redone, and its use should be added back. */ 142 143 #ifdef PBMS_DEBUG 144 145 /* 146 * Print the error message (preceded by the driver and function) 147 * specified by the string literal fmt (followed by newline) if 148 * pbmsdebug is greater than n. The macro may only be used in the 149 * scope of sc, which must be castable to struct device *. There must 150 * be at least one vararg. Do not define PBMS_DEBUG on non-C99 151 * compilers. 152 */ 153 154 #define DPRINTFN(n, fmt, ...) \ 155 do { \ 156 if (pbmsdebug > (n)) \ 157 logprintf("%s: %s: " fmt "\n", \ 158 ((struct device *) sc)->dv_xname, \ 159 __func__, __VA_ARGS__); \ 160 } while ( /* CONSTCOND */ 0) 161 162 int pbmsdebug = 0; 163 164 #endif /* PBMS_DEBUG */ 165 166 167 /* 168 * Magic numbers. 169 */ 170 171 172 /* The amount of data transfered by the USB device. */ 173 #define PBMS_DATA_LEN 81 174 175 /* The maximum number of sensors. */ 176 #define PBMS_X_SENSORS 26 177 #define PBMS_Y_SENSORS 16 178 #define PBMS_SENSORS (PBMS_X_SENSORS + PBMS_Y_SENSORS) 179 180 /* 181 * Parameters for supported devices. For generality, these parameters 182 * can be different for each device. The meanings of the parameters 183 * are as follows. 184 * 185 * desc: A printable description used for dmesg output. 186 * 187 * noise: Amount of noise in the computed position. This controls 188 * how large a change must be to get reported, and how 189 * large enough changes are smoothed. A good value can 190 * probably only be found experimentally, but something around 191 * 16 seems suitable. 192 * 193 * product: The product ID of the trackpad. 194 * 195 * 196 * threshold: Accumulated changes less than this are ignored. A good 197 * value could be determined experimentally, but 5 is a 198 * reasonable guess. 199 * 200 * vendor: The vendor ID. Currently USB_VENDOR_APPLE for all devices. 201 * 202 * x_factor: Factor used in computations with X-coordinates. If the 203 * x-resolution of the display is x, this should be 204 * (x + 1) / (x_sensors - 1). Other values work fine, but 205 * then the aspect ratio is not necessarily kept. 206 * 207 * x_sensors: The number of sensors in the X-direction. 208 * 209 * y_factor: As x_factors, but for Y-coordinates. 210 * 211 * y_sensors: The number of sensors in the Y-direction. 212 */ 213 214 struct pbms_dev { 215 const char *descr; /* Description of the driver (for dmesg). */ 216 int noise; /* Amount of noise in the computed position. */ 217 int threshold; /* Changes less than this are ignored. */ 218 int x_factor; /* Factor used in computation with X-coordinates. */ 219 int x_sensors; /* The number of X-sensors. */ 220 int y_factor; /* Factor used in computation with Y-coordinates. */ 221 int y_sensors; /* The number of Y-sensors. */ 222 uint16_t product; /* Product ID. */ 223 uint16_t vendor; /* The vendor ID. */ 224 }; 225 226 /* Devices supported by this driver. */ 227 static struct pbms_dev pbms_devices[] = 228 { 229 #define POWERBOOK_TOUCHPAD(inches, prod, x_fact, x_sens, y_fact) \ 230 { \ 231 .descr = #inches " inch PowerBook Trackpad", \ 232 .vendor = USB_VENDOR_APPLE, \ 233 .product = (prod), \ 234 .noise = 16, \ 235 .threshold = 5, \ 236 .x_factor = (x_fact), \ 237 .x_sensors = (x_sens), \ 238 .y_factor = (y_fact), \ 239 .y_sensors = 16 \ 240 } 241 /* 12 inch PowerBooks */ 242 POWERBOOK_TOUCHPAD(12, 0x030a, 69, 16, 52), /* XXX Not tested. */ 243 /* 15 inch PowerBooks */ 244 POWERBOOK_TOUCHPAD(15, 0x020e, 85, 16, 57), /* XXX Not tested. */ 245 POWERBOOK_TOUCHPAD(15, 0x020f, 85, 16, 57), 246 /* 17 inch PowerBooks */ 247 POWERBOOK_TOUCHPAD(17, 0x020d, 71, 26, 68) /* XXX Not tested. */ 248 #undef POWERBOOK_TOUCHPAD 249 }; 250 251 /* The number of supported devices. */ 252 #define PBMS_NUM_DEVICES (sizeof(pbms_devices) / sizeof(pbms_devices[0])) 253 254 255 /* 256 * Types and prototypes. 257 */ 258 259 260 /* Device data. */ 261 struct pbms_softc { 262 struct uhidev sc_hdev; /* USB parent (got the struct device). */ 263 int sc_acc[PBMS_SENSORS]; /* Accumulated sensor values. */ 264 signed char sc_prev[PBMS_SENSORS]; /* Previous sample. */ 265 signed char sc_sample[PBMS_SENSORS]; /* Current sample. */ 266 struct device *sc_wsmousedev; /* WSMouse device. */ 267 int sc_noise; /* Amount of noise. */ 268 int sc_theshold; /* Threshold value. */ 269 int sc_x; /* Virtual position in horizontal 270 * direction (wsmouse position). */ 271 int sc_x_factor; /* X-coordinate factor. */ 272 int sc_x_raw; /* X-position of finger on trackpad. */ 273 int sc_x_sensors; /* Number of X-sensors. */ 274 int sc_y; /* Virtual position in vertical direction 275 * (wsmouse position). */ 276 int sc_y_factor; /* Y-coordinate factor. */ 277 int sc_y_raw; /* Y-position of finger on trackpad. */ 278 int sc_y_sensors; /* Number of Y-sensors. */ 279 uint32_t sc_buttons; /* Button state. */ 280 uint32_t sc_status; /* Status flags. */ 281 #define PBMS_ENABLED 1 /* Is the device enabled? */ 282 #define PBMS_DYING 2 /* Is the device dying? */ 283 #define PBMS_VALID 4 /* Is the previous sample valid? */ 284 }; 285 286 287 /* Static function prototypes. */ 288 static void pbms_intr(struct uhidev *, void *, unsigned int); 289 static int pbms_enable(void *); 290 static void pbms_disable(void *); 291 static int pbms_ioctl(void *, unsigned long, caddr_t, int, struct lwp *); 292 static void reorder_sample(signed char *, signed char *); 293 static int compute_delta(struct pbms_softc *, int *, int *, int *, uint32_t *); 294 static int detect_pos(int *, int, int, int, int *, int *); 295 static int smooth_pos(int, int, int); 296 297 /* Access methods for wsmouse. */ 298 const struct wsmouse_accessops pbms_accessops = { 299 pbms_enable, 300 pbms_ioctl, 301 pbms_disable, 302 }; 303 304 /* This take cares also of the basic device registration. */ 305 USB_DECLARE_DRIVER(pbms); 306 307 308 /* 309 * Basic driver. 310 */ 311 312 313 /* Try to match the device at some uhidev. */ 314 315 int 316 pbms_match(struct device *parent, struct cfdata *match, void *aux) 317 { 318 struct uhidev_attach_arg *uha = aux; 319 usb_device_descriptor_t *udd; 320 int i; 321 uint16_t vendor, product; 322 323 /* 324 * We just check if the vendor and product IDs have the magic numbers 325 * we expect. 326 */ 327 if ((udd = usbd_get_device_descriptor(uha->parent->sc_udev)) != NULL) { 328 vendor = UGETW(udd->idVendor); 329 product = UGETW(udd->idProduct); 330 for (i = 0; i < PBMS_NUM_DEVICES; i++) { 331 if (vendor == pbms_devices[i].vendor && 332 product == pbms_devices[i].product) 333 return UMATCH_IFACECLASS; 334 } 335 } 336 return UMATCH_NONE; 337 } 338 339 340 /* Attach the device. */ 341 342 void 343 pbms_attach(struct device *parent, struct device *self, void *aux) 344 { 345 struct wsmousedev_attach_args a; 346 struct uhidev_attach_arg *uha = aux; 347 struct pbms_dev *pd; 348 struct pbms_softc *sc = (struct pbms_softc *)self; 349 usb_device_descriptor_t *udd; 350 int i; 351 uint16_t vendor, product; 352 353 sc->sc_hdev.sc_intr = pbms_intr; 354 sc->sc_hdev.sc_parent = uha->parent; 355 sc->sc_hdev.sc_report_id = uha->reportid; 356 357 /* Fill in device-specific parameters. */ 358 if ((udd = usbd_get_device_descriptor(uha->parent->sc_udev)) != NULL) { 359 product = UGETW(udd->idProduct); 360 vendor = UGETW(udd->idVendor); 361 for (i = 0; i < PBMS_NUM_DEVICES; i++) { 362 pd = &pbms_devices[i]; 363 if (product == pd->product && vendor == pd->vendor) { 364 printf(": %s\n", pd->descr); 365 sc->sc_noise = pd->noise; 366 sc->sc_theshold = pd->threshold; 367 sc->sc_x_factor = pd->x_factor; 368 sc->sc_x_sensors = pd->x_sensors; 369 sc->sc_y_factor = pd->y_factor; 370 sc->sc_y_sensors = pd->y_sensors; 371 break; 372 } 373 } 374 } 375 KASSERT(0 <= sc->sc_x_sensors && sc->sc_x_sensors <= PBMS_X_SENSORS); 376 KASSERT(0 <= sc->sc_y_sensors && sc->sc_y_sensors <= PBMS_Y_SENSORS); 377 378 sc->sc_status = 0; 379 380 a.accessops = &pbms_accessops; 381 a.accesscookie = sc; 382 383 sc->sc_wsmousedev = config_found(self, &a, wsmousedevprint); 384 385 USB_ATTACH_SUCCESS_RETURN; 386 } 387 388 389 /* Detach the device. */ 390 391 int 392 pbms_detach(struct device *self, int flags) 393 { 394 struct pbms_softc *sc = (struct pbms_softc *)self; 395 int ret; 396 397 /* The wsmouse driver does all the work. */ 398 ret = 0; 399 if (sc->sc_wsmousedev != NULL) 400 ret = config_detach(sc->sc_wsmousedev, flags); 401 402 return ret; 403 } 404 405 406 /* Activate the device. */ 407 408 int 409 pbms_activate(device_ptr_t self, enum devact act) 410 { 411 struct pbms_softc *sc = (struct pbms_softc *)self; 412 int ret; 413 414 if (act == DVACT_DEACTIVATE) { 415 ret = 0; 416 if (sc->sc_wsmousedev != NULL) 417 ret = config_deactivate(sc->sc_wsmousedev); 418 sc->sc_status |= PBMS_DYING; 419 return ret; 420 } 421 return EOPNOTSUPP; 422 } 423 424 425 /* Enable the device. */ 426 427 static int 428 pbms_enable(void *v) 429 { 430 struct pbms_softc *sc = v; 431 432 /* Check that we are not detaching or already enabled. */ 433 if (sc->sc_status & PBMS_DYING) 434 return EIO; 435 if (sc->sc_status & PBMS_ENABLED) 436 return EBUSY; 437 438 sc->sc_status |= PBMS_ENABLED; 439 sc->sc_status &= ~PBMS_VALID; 440 sc->sc_buttons = 0; 441 memset(sc->sc_sample, 0, sizeof(sc->sc_sample)); 442 443 return uhidev_open(&sc->sc_hdev); 444 } 445 446 447 /* Disable the device. */ 448 449 static void 450 pbms_disable(void *v) 451 { 452 struct pbms_softc *sc = v; 453 454 if (!(sc->sc_status & PBMS_ENABLED)) 455 return; 456 457 sc->sc_status &= ~PBMS_ENABLED; 458 uhidev_close(&sc->sc_hdev); 459 } 460 461 462 /* XXX ioctl not implemented. */ 463 464 static int 465 pbms_ioctl(void *v, unsigned long cmd, caddr_t data, int flag, struct lwp *p) 466 { 467 return EPASSTHROUGH; 468 } 469 470 471 /* 472 * Interrupts & pointer movement. 473 */ 474 475 476 /* Handle interrupts. */ 477 478 void 479 pbms_intr(struct uhidev *addr, void *ibuf, unsigned int len) 480 { 481 struct pbms_softc *sc = (struct pbms_softc *)addr; 482 signed char *data; 483 int dx, dy, dz, i, s; 484 uint32_t buttons; 485 486 /* Ignore incomplete data packets. */ 487 if (len != PBMS_DATA_LEN) 488 return; 489 data = ibuf; 490 491 /* The last byte is 1 if the button is pressed and 0 otherwise. */ 492 buttons = !!data[PBMS_DATA_LEN - 1]; 493 494 /* Everything below assumes that the sample is reordered. */ 495 reorder_sample(sc->sc_sample, data); 496 497 /* Is this the first sample? */ 498 if (!(sc->sc_status & PBMS_VALID)) { 499 sc->sc_status |= PBMS_VALID; 500 sc->sc_x = sc->sc_y = -1; 501 sc->sc_x_raw = sc->sc_y_raw = -1; 502 memcpy(sc->sc_prev, sc->sc_sample, sizeof(sc->sc_prev)); 503 memset(sc->sc_acc, 0, sizeof(sc->sc_acc)); 504 return; 505 } 506 /* Accumulate the sensor change while keeping it nonnegative. */ 507 for (i = 0; i < PBMS_SENSORS; i++) { 508 sc->sc_acc[i] += sc->sc_sample[i] - sc->sc_prev[i]; 509 if (sc->sc_acc[i] < 0) 510 sc->sc_acc[i] = 0; 511 } 512 memcpy(sc->sc_prev, sc->sc_sample, sizeof(sc->sc_prev)); 513 514 /* Compute change. */ 515 dx = dy = dz = 0; 516 if (!compute_delta(sc, &dx, &dy, &dz, &buttons)) 517 return; 518 519 /* Report to wsmouse. */ 520 if ((dx != 0 || dy != 0 || dz != 0 || buttons != sc->sc_buttons) && 521 sc->sc_wsmousedev != NULL) { 522 s = spltty(); 523 wsmouse_input(sc->sc_wsmousedev, buttons, dx, -dy, dz, 524 WSMOUSE_INPUT_DELTA); 525 splx(s); 526 } 527 sc->sc_buttons = buttons; 528 } 529 530 531 /* 532 * Reorder the sensor values so that all the X-sensors are before the 533 * Y-sensors in the natural order. Note that this might have to be 534 * rewritten if PBMS_X_SENSORS or PBMS_Y_SENSORS change. 535 */ 536 537 static void 538 reorder_sample(signed char *to, signed char *from) 539 { 540 int i; 541 542 for (i = 0; i < 8; i++) { 543 /* X-sensors. */ 544 to[i] = from[5 * i + 2]; 545 to[i + 8] = from[5 * i + 4]; 546 to[i + 16] = from[5 * i + 42]; 547 #if 0 548 /* 549 * XXX This seems to introduce random ventical jumps, so 550 * we ignore these sensors until we figure out their meaning. 551 */ 552 if (i < 2) 553 to[i + 24] = from[5 * i + 44]; 554 #endif /* 0 */ 555 /* Y-sensors. */ 556 to[i + 26] = from[5 * i + 1]; 557 to[i + 34] = from[5 * i + 3]; 558 } 559 } 560 561 562 /* 563 * Compute the change in x, y and z direction, update the button state 564 * (to simulate more than one button, scrolling etc.), and update the 565 * history. Note that dx, dy, dz and buttons are modified only if 566 * corresponding pressure is detected and should thus be initialised 567 * before the call. Return 0 on error. 568 */ 569 570 /* XXX Could we report something useful in dz? */ 571 572 static int 573 compute_delta(struct pbms_softc *sc, int *dx, int *dy, int *dz, 574 uint32_t * buttons) 575 { 576 int x_det, y_det, x_raw, y_raw, x_fingers, y_fingers, fingers, x, y; 577 578 x_det = detect_pos(sc->sc_acc, sc->sc_x_sensors, sc->sc_theshold, 579 sc->sc_x_factor, &x_raw, &x_fingers); 580 y_det = detect_pos(sc->sc_acc + PBMS_X_SENSORS, sc->sc_y_sensors, 581 sc->sc_theshold, sc->sc_y_factor, 582 &y_raw, &y_fingers); 583 fingers = max(x_fingers, y_fingers); 584 585 /* Check the number of fingers and if we have detected a position. */ 586 if (fingers > 1) { 587 /* More than one finger detected, resetting. */ 588 memset(sc->sc_acc, 0, sizeof(sc->sc_acc)); 589 sc->sc_x_raw = sc->sc_y_raw = sc->sc_x = sc->sc_y = -1; 590 return 0; 591 } else if (x_det == 0 && y_det == 0) { 592 /* No position detected, resetting. */ 593 memset(sc->sc_acc, 0, sizeof(sc->sc_acc)); 594 sc->sc_x_raw = sc->sc_y_raw = sc->sc_x = sc->sc_y = -1; 595 } else if (x_det > 0 && y_det > 0) { 596 /* Smooth position. */ 597 if (sc->sc_x_raw >= 0) { 598 sc->sc_x_raw = (3 * sc->sc_x_raw + x_raw) / 4; 599 sc->sc_y_raw = (3 * sc->sc_y_raw + y_raw) / 4; 600 /* 601 * Compute virtual position and change if we already 602 * have a decent position. 603 */ 604 if (sc->sc_x >= 0) { 605 x = smooth_pos(sc->sc_x, sc->sc_x_raw, 606 sc->sc_noise); 607 y = smooth_pos(sc->sc_y, sc->sc_y_raw, 608 sc->sc_noise); 609 *dx = x - sc->sc_x; 610 *dy = y - sc->sc_y; 611 sc->sc_x = x; 612 sc->sc_y = y; 613 } else { 614 /* Initialise virtual position. */ 615 sc->sc_x = sc->sc_x_raw; 616 sc->sc_y = sc->sc_y_raw; 617 } 618 } else { 619 /* Initialise raw position. */ 620 sc->sc_x_raw = x_raw; 621 sc->sc_y_raw = y_raw; 622 } 623 } 624 return 1; 625 } 626 627 628 /* 629 * Compute the new smoothed position from the previous smoothed position 630 * and the raw position. 631 */ 632 633 static int 634 smooth_pos(int pos_old, int pos_raw, int noise) 635 { 636 int ad, delta; 637 638 delta = pos_raw - pos_old; 639 ad = abs(delta); 640 641 /* Too small changes are ignored. */ 642 if (ad < noise / 2) 643 delta = 0; 644 /* A bit larger changes are smoothed. */ 645 else if (ad < noise) 646 delta /= 4; 647 else if (ad < 2 * noise) 648 delta /= 2; 649 650 return pos_old + delta; 651 } 652 653 654 /* 655 * Detect the position of the finger. Returns the total pressure. 656 * The position is returned in pos_ret and the number of fingers 657 * is returned in fingers_ret. The position returned in pos_ret 658 * is in [0, (n_sensors - 1) * factor - 1]. 659 */ 660 661 static int 662 detect_pos(int *sensors, int n_sensors, int threshold, int fact, 663 int *pos_ret, int *fingers_ret) 664 { 665 int i, w, s; 666 667 /* 668 * Compute the number of fingers, total pressure, and weighted 669 * position of the fingers. 670 */ 671 *fingers_ret = 0; 672 w = s = 0; 673 for (i = 0; i < n_sensors; i++) { 674 if (sensors[i] >= threshold) { 675 if (i == 0 || sensors[i - 1] < threshold) 676 *fingers_ret += 1; 677 s += sensors[i]; 678 w += sensors[i] * i; 679 } 680 } 681 682 if (s > 0) 683 *pos_ret = w * fact / s; 684 685 return s; 686 } 687