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1 <?xml version="1.0" encoding="UTF-8"?> 2 <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" 3 "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> 4 5 <book id="iioid"> 6 <bookinfo> 7 <title>Industrial I/O driver developer's guide </title> 8 9 <authorgroup> 10 <author> 11 <firstname>Daniel</firstname> 12 <surname>Baluta</surname> 13 <affiliation> 14 <address> 15 <email>daniel.baluta@intel.com</email> 16 </address> 17 </affiliation> 18 </author> 19 </authorgroup> 20 21 <copyright> 22 <year>2015</year> 23 <holder>Intel Corporation</holder> 24 </copyright> 25 26 <legalnotice> 27 <para> 28 This documentation is free software; you can redistribute 29 it and/or modify it under the terms of the GNU General Public 30 License version 2. 31 </para> 32 </legalnotice> 33 </bookinfo> 34 35 <toc></toc> 36 37 <chapter id="intro"> 38 <title>Introduction</title> 39 <para> 40 The main purpose of the Industrial I/O subsystem (IIO) is to provide 41 support for devices that in some sense perform either analog-to-digital 42 conversion (ADC) or digital-to-analog conversion (DAC) or both. The aim 43 is to fill the gap between the somewhat similar hwmon and input 44 subsystems. 45 Hwmon is directed at low sample rate sensors used to monitor and 46 control the system itself, like fan speed control or temperature 47 measurement. Input is, as its name suggests, focused on human interaction 48 input devices (keyboard, mouse, touchscreen). In some cases there is 49 considerable overlap between these and IIO. 50 </para> 51 <para> 52 Devices that fall into this category include: 53 <itemizedlist> 54 <listitem> 55 analog to digital converters (ADCs) 56 </listitem> 57 <listitem> 58 accelerometers 59 </listitem> 60 <listitem> 61 capacitance to digital converters (CDCs) 62 </listitem> 63 <listitem> 64 digital to analog converters (DACs) 65 </listitem> 66 <listitem> 67 gyroscopes 68 </listitem> 69 <listitem> 70 inertial measurement units (IMUs) 71 </listitem> 72 <listitem> 73 color and light sensors 74 </listitem> 75 <listitem> 76 magnetometers 77 </listitem> 78 <listitem> 79 pressure sensors 80 </listitem> 81 <listitem> 82 proximity sensors 83 </listitem> 84 <listitem> 85 temperature sensors 86 </listitem> 87 </itemizedlist> 88 Usually these sensors are connected via SPI or I2C. A common use case of the 89 sensors devices is to have combined functionality (e.g. light plus proximity 90 sensor). 91 </para> 92 </chapter> 93 <chapter id='iiosubsys'> 94 <title>Industrial I/O core</title> 95 <para> 96 The Industrial I/O core offers: 97 <itemizedlist> 98 <listitem> 99 a unified framework for writing drivers for many different types of 100 embedded sensors. 101 </listitem> 102 <listitem> 103 a standard interface to user space applications manipulating sensors. 104 </listitem> 105 </itemizedlist> 106 The implementation can be found under <filename> 107 drivers/iio/industrialio-*</filename> 108 </para> 109 <sect1 id="iiodevice"> 110 <title> Industrial I/O devices </title> 111 112 !Finclude/linux/iio/iio.h iio_dev 113 !Fdrivers/iio/industrialio-core.c iio_device_alloc 114 !Fdrivers/iio/industrialio-core.c iio_device_free 115 !Fdrivers/iio/industrialio-core.c iio_device_register 116 !Fdrivers/iio/industrialio-core.c iio_device_unregister 117 118 <para> 119 An IIO device usually corresponds to a single hardware sensor and it 120 provides all the information needed by a driver handling a device. 121 Let's first have a look at the functionality embedded in an IIO 122 device then we will show how a device driver makes use of an IIO 123 device. 124 </para> 125 <para> 126 There are two ways for a user space application to interact 127 with an IIO driver. 128 <itemizedlist> 129 <listitem> 130 <filename>/sys/bus/iio/iio:deviceX/</filename>, this 131 represents a hardware sensor and groups together the data 132 channels of the same chip. 133 </listitem> 134 <listitem> 135 <filename>/dev/iio:deviceX</filename>, character device node 136 interface used for buffered data transfer and for events information 137 retrieval. 138 </listitem> 139 </itemizedlist> 140 </para> 141 A typical IIO driver will register itself as an I2C or SPI driver and will 142 create two routines, <function> probe </function> and <function> remove 143 </function>. At <function>probe</function>: 144 <itemizedlist> 145 <listitem>call <function>iio_device_alloc</function>, which allocates memory 146 for an IIO device. 147 </listitem> 148 <listitem> initialize IIO device fields with driver specific information 149 (e.g. device name, device channels). 150 </listitem> 151 <listitem>call <function> iio_device_register</function>, this registers the 152 device with the IIO core. After this call the device is ready to accept 153 requests from user space applications. 154 </listitem> 155 </itemizedlist> 156 At <function>remove</function>, we free the resources allocated in 157 <function>probe</function> in reverse order: 158 <itemizedlist> 159 <listitem><function>iio_device_unregister</function>, unregister the device 160 from the IIO core. 161 </listitem> 162 <listitem><function>iio_device_free</function>, free the memory allocated 163 for the IIO device. 164 </listitem> 165 </itemizedlist> 166 167 <sect2 id="iioattr"> <title> IIO device sysfs interface </title> 168 <para> 169 Attributes are sysfs files used to expose chip info and also allowing 170 applications to set various configuration parameters. For device 171 with index X, attributes can be found under 172 <filename>/sys/bus/iio/iio:deviceX/ </filename> directory. 173 Common attributes are: 174 <itemizedlist> 175 <listitem><filename>name</filename>, description of the physical 176 chip. 177 </listitem> 178 <listitem><filename>dev</filename>, shows the major:minor pair 179 associated with <filename>/dev/iio:deviceX</filename> node. 180 </listitem> 181 <listitem><filename>sampling_frequency_available</filename>, 182 available discrete set of sampling frequency values for 183 device. 184 </listitem> 185 </itemizedlist> 186 Available standard attributes for IIO devices are described in the 187 <filename>Documentation/ABI/testing/sysfs-bus-iio </filename> file 188 in the Linux kernel sources. 189 </para> 190 </sect2> 191 <sect2 id="iiochannel"> <title> IIO device channels </title> 192 !Finclude/linux/iio/iio.h iio_chan_spec structure. 193 <para> 194 An IIO device channel is a representation of a data channel. An 195 IIO device can have one or multiple channels. For example: 196 <itemizedlist> 197 <listitem> 198 a thermometer sensor has one channel representing the 199 temperature measurement. 200 </listitem> 201 <listitem> 202 a light sensor with two channels indicating the measurements in 203 the visible and infrared spectrum. 204 </listitem> 205 <listitem> 206 an accelerometer can have up to 3 channels representing 207 acceleration on X, Y and Z axes. 208 </listitem> 209 </itemizedlist> 210 An IIO channel is described by the <type> struct iio_chan_spec 211 </type>. A thermometer driver for the temperature sensor in the 212 example above would have to describe its channel as follows: 213 <programlisting> 214 static const struct iio_chan_spec temp_channel[] = { 215 { 216 .type = IIO_TEMP, 217 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), 218 }, 219 }; 220 221 </programlisting> 222 Channel sysfs attributes exposed to userspace are specified in 223 the form of <emphasis>bitmasks</emphasis>. Depending on their 224 shared info, attributes can be set in one of the following masks: 225 <itemizedlist> 226 <listitem><emphasis>info_mask_separate</emphasis>, attributes will 227 be specific to this channel</listitem> 228 <listitem><emphasis>info_mask_shared_by_type</emphasis>, 229 attributes are shared by all channels of the same type</listitem> 230 <listitem><emphasis>info_mask_shared_by_dir</emphasis>, attributes 231 are shared by all channels of the same direction </listitem> 232 <listitem><emphasis>info_mask_shared_by_all</emphasis>, 233 attributes are shared by all channels</listitem> 234 </itemizedlist> 235 When there are multiple data channels per channel type we have two 236 ways to distinguish between them: 237 <itemizedlist> 238 <listitem> set <emphasis> .modified</emphasis> field of <type> 239 iio_chan_spec</type> to 1. Modifiers are specified using 240 <emphasis>.channel2</emphasis> field of the same 241 <type>iio_chan_spec</type> structure and are used to indicate a 242 physically unique characteristic of the channel such as its direction 243 or spectral response. For example, a light sensor can have two channels, 244 one for infrared light and one for both infrared and visible light. 245 </listitem> 246 <listitem> set <emphasis>.indexed </emphasis> field of 247 <type>iio_chan_spec</type> to 1. In this case the channel is 248 simply another instance with an index specified by the 249 <emphasis>.channel</emphasis> field. 250 </listitem> 251 </itemizedlist> 252 Here is how we can make use of the channel's modifiers: 253 <programlisting> 254 static const struct iio_chan_spec light_channels[] = { 255 { 256 .type = IIO_INTENSITY, 257 .modified = 1, 258 .channel2 = IIO_MOD_LIGHT_IR, 259 .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), 260 .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ), 261 }, 262 { 263 .type = IIO_INTENSITY, 264 .modified = 1, 265 .channel2 = IIO_MOD_LIGHT_BOTH, 266 .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), 267 .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ), 268 }, 269 { 270 .type = IIO_LIGHT, 271 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), 272 .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ), 273 }, 274 275 } 276 </programlisting> 277 This channel's definition will generate two separate sysfs files 278 for raw data retrieval: 279 <itemizedlist> 280 <listitem> 281 <filename>/sys/bus/iio/iio:deviceX/in_intensity_ir_raw</filename> 282 </listitem> 283 <listitem> 284 <filename>/sys/bus/iio/iio:deviceX/in_intensity_both_raw</filename> 285 </listitem> 286 </itemizedlist> 287 one file for processed data: 288 <itemizedlist> 289 <listitem> 290 <filename>/sys/bus/iio/iio:deviceX/in_illuminance_input 291 </filename> 292 </listitem> 293 </itemizedlist> 294 and one shared sysfs file for sampling frequency: 295 <itemizedlist> 296 <listitem> 297 <filename>/sys/bus/iio/iio:deviceX/sampling_frequency. 298 </filename> 299 </listitem> 300 </itemizedlist> 301 </para> 302 <para> 303 Here is how we can make use of the channel's indexing: 304 <programlisting> 305 static const struct iio_chan_spec light_channels[] = { 306 { 307 .type = IIO_VOLTAGE, 308 .indexed = 1, 309 .channel = 0, 310 .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), 311 }, 312 { 313 .type = IIO_VOLTAGE, 314 .indexed = 1, 315 .channel = 1, 316 .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), 317 }, 318 } 319 </programlisting> 320 This will generate two separate attributes files for raw data 321 retrieval: 322 <itemizedlist> 323 <listitem> 324 <filename>/sys/bus/iio/devices/iio:deviceX/in_voltage0_raw</filename>, 325 representing voltage measurement for channel 0. 326 </listitem> 327 <listitem> 328 <filename>/sys/bus/iio/devices/iio:deviceX/in_voltage1_raw</filename>, 329 representing voltage measurement for channel 1. 330 </listitem> 331 </itemizedlist> 332 </para> 333 </sect2> 334 </sect1> 335 336 <sect1 id="iiobuffer"> <title> Industrial I/O buffers </title> 337 !Finclude/linux/iio/buffer.h iio_buffer 338 !Edrivers/iio/industrialio-buffer.c 339 340 <para> 341 The Industrial I/O core offers a way for continuous data capture 342 based on a trigger source. Multiple data channels can be read at once 343 from <filename>/dev/iio:deviceX</filename> character device node, 344 thus reducing the CPU load. 345 </para> 346 347 <sect2 id="iiobuffersysfs"> 348 <title>IIO buffer sysfs interface </title> 349 <para> 350 An IIO buffer has an associated attributes directory under <filename> 351 /sys/bus/iio/iio:deviceX/buffer/</filename>. Here are the existing 352 attributes: 353 <itemizedlist> 354 <listitem> 355 <emphasis>length</emphasis>, the total number of data samples 356 (capacity) that can be stored by the buffer. 357 </listitem> 358 <listitem> 359 <emphasis>enable</emphasis>, activate buffer capture. 360 </listitem> 361 </itemizedlist> 362 363 </para> 364 </sect2> 365 <sect2 id="iiobuffersetup"> <title> IIO buffer setup </title> 366 <para>The meta information associated with a channel reading 367 placed in a buffer is called a <emphasis> scan element </emphasis>. 368 The important bits configuring scan elements are exposed to 369 userspace applications via the <filename> 370 /sys/bus/iio/iio:deviceX/scan_elements/</filename> directory. This 371 file contains attributes of the following form: 372 <itemizedlist> 373 <listitem><emphasis>enable</emphasis>, used for enabling a channel. 374 If and only if its attribute is non zero, then a triggered capture 375 will contain data samples for this channel. 376 </listitem> 377 <listitem><emphasis>type</emphasis>, description of the scan element 378 data storage within the buffer and hence the form in which it is 379 read from user space. Format is <emphasis> 380 [be|le]:[s|u]bits/storagebitsXrepeat[>>shift] </emphasis>. 381 <itemizedlist> 382 <listitem> <emphasis>be</emphasis> or <emphasis>le</emphasis>, specifies 383 big or little endian. 384 </listitem> 385 <listitem> 386 <emphasis>s </emphasis>or <emphasis>u</emphasis>, specifies if 387 signed (2's complement) or unsigned. 388 </listitem> 389 <listitem><emphasis>bits</emphasis>, is the number of valid data 390 bits. 391 </listitem> 392 <listitem><emphasis>storagebits</emphasis>, is the number of bits 393 (after padding) that it occupies in the buffer. 394 </listitem> 395 <listitem> 396 <emphasis>shift</emphasis>, if specified, is the shift that needs 397 to be applied prior to masking out unused bits. 398 </listitem> 399 <listitem> 400 <emphasis>repeat</emphasis>, specifies the number of bits/storagebits 401 repetitions. When the repeat element is 0 or 1, then the repeat 402 value is omitted. 403 </listitem> 404 </itemizedlist> 405 </listitem> 406 </itemizedlist> 407 For example, a driver for a 3-axis accelerometer with 12 bit 408 resolution where data is stored in two 8-bits registers as 409 follows: 410 <programlisting> 411 7 6 5 4 3 2 1 0 412 +---+---+---+---+---+---+---+---+ 413 |D3 |D2 |D1 |D0 | X | X | X | X | (LOW byte, address 0x06) 414 +---+---+---+---+---+---+---+---+ 415 416 7 6 5 4 3 2 1 0 417 +---+---+---+---+---+---+---+---+ 418 |D11|D10|D9 |D8 |D7 |D6 |D5 |D4 | (HIGH byte, address 0x07) 419 +---+---+---+---+---+---+---+---+ 420 </programlisting> 421 422 will have the following scan element type for each axis: 423 <programlisting> 424 $ cat /sys/bus/iio/devices/iio:device0/scan_elements/in_accel_y_type 425 le:s12/16>>4 426 </programlisting> 427 A user space application will interpret data samples read from the 428 buffer as two byte little endian signed data, that needs a 4 bits 429 right shift before masking out the 12 valid bits of data. 430 </para> 431 <para> 432 For implementing buffer support a driver should initialize the following 433 fields in <type>iio_chan_spec</type> definition: 434 <programlisting> 435 struct iio_chan_spec { 436 /* other members */ 437 int scan_index 438 struct { 439 char sign; 440 u8 realbits; 441 u8 storagebits; 442 u8 shift; 443 u8 repeat; 444 enum iio_endian endianness; 445 } scan_type; 446 }; 447 </programlisting> 448 The driver implementing the accelerometer described above will 449 have the following channel definition: 450 <programlisting> 451 struct struct iio_chan_spec accel_channels[] = { 452 { 453 .type = IIO_ACCEL, 454 .modified = 1, 455 .channel2 = IIO_MOD_X, 456 /* other stuff here */ 457 .scan_index = 0, 458 .scan_type = { 459 .sign = 's', 460 .realbits = 12, 461 .storagebits = 16, 462 .shift = 4, 463 .endianness = IIO_LE, 464 }, 465 } 466 /* similar for Y (with channel2 = IIO_MOD_Y, scan_index = 1) 467 * and Z (with channel2 = IIO_MOD_Z, scan_index = 2) axis 468 */ 469 } 470 </programlisting> 471 </para> 472 <para> 473 Here <emphasis> scan_index </emphasis> defines the order in which 474 the enabled channels are placed inside the buffer. Channels with a lower 475 scan_index will be placed before channels with a higher index. Each 476 channel needs to have a unique scan_index. 477 </para> 478 <para> 479 Setting scan_index to -1 can be used to indicate that the specific 480 channel does not support buffered capture. In this case no entries will 481 be created for the channel in the scan_elements directory. 482 </para> 483 </sect2> 484 </sect1> 485 486 <sect1 id="iiotrigger"> <title> Industrial I/O triggers </title> 487 !Finclude/linux/iio/trigger.h iio_trigger 488 !Edrivers/iio/industrialio-trigger.c 489 <para> 490 In many situations it is useful for a driver to be able to 491 capture data based on some external event (trigger) as opposed 492 to periodically polling for data. An IIO trigger can be provided 493 by a device driver that also has an IIO device based on hardware 494 generated events (e.g. data ready or threshold exceeded) or 495 provided by a separate driver from an independent interrupt 496 source (e.g. GPIO line connected to some external system, timer 497 interrupt or user space writing a specific file in sysfs). A 498 trigger may initiate data capture for a number of sensors and 499 also it may be completely unrelated to the sensor itself. 500 </para> 501 502 <sect2 id="iiotrigsysfs"> <title> IIO trigger sysfs interface </title> 503 There are two locations in sysfs related to triggers: 504 <itemizedlist> 505 <listitem><filename>/sys/bus/iio/devices/triggerY</filename>, 506 this file is created once an IIO trigger is registered with 507 the IIO core and corresponds to trigger with index Y. Because 508 triggers can be very different depending on type there are few 509 standard attributes that we can describe here: 510 <itemizedlist> 511 <listitem> 512 <emphasis>name</emphasis>, trigger name that can be later 513 used for association with a device. 514 </listitem> 515 <listitem> 516 <emphasis>sampling_frequency</emphasis>, some timer based 517 triggers use this attribute to specify the frequency for 518 trigger calls. 519 </listitem> 520 </itemizedlist> 521 </listitem> 522 <listitem> 523 <filename>/sys/bus/iio/devices/iio:deviceX/trigger/</filename>, this 524 directory is created once the device supports a triggered 525 buffer. We can associate a trigger with our device by writing 526 the trigger's name in the <filename>current_trigger</filename> file. 527 </listitem> 528 </itemizedlist> 529 </sect2> 530 531 <sect2 id="iiotrigattr"> <title> IIO trigger setup</title> 532 533 <para> 534 Let's see a simple example of how to setup a trigger to be used 535 by a driver. 536 537 <programlisting> 538 struct iio_trigger_ops trigger_ops = { 539 .set_trigger_state = sample_trigger_state, 540 .validate_device = sample_validate_device, 541 } 542 543 struct iio_trigger *trig; 544 545 /* first, allocate memory for our trigger */ 546 trig = iio_trigger_alloc(dev, "trig-%s-%d", name, idx); 547 548 /* setup trigger operations field */ 549 trig->ops = &trigger_ops; 550 551 /* now register the trigger with the IIO core */ 552 iio_trigger_register(trig); 553 </programlisting> 554 </para> 555 </sect2> 556 557 <sect2 id="iiotrigsetup"> <title> IIO trigger ops</title> 558 !Finclude/linux/iio/trigger.h iio_trigger_ops 559 <para> 560 Notice that a trigger has a set of operations attached: 561 <itemizedlist> 562 <listitem> 563 <function>set_trigger_state</function>, switch the trigger on/off 564 on demand. 565 </listitem> 566 <listitem> 567 <function>validate_device</function>, function to validate the 568 device when the current trigger gets changed. 569 </listitem> 570 </itemizedlist> 571 </para> 572 </sect2> 573 </sect1> 574 <sect1 id="iiotriggered_buffer"> 575 <title> Industrial I/O triggered buffers </title> 576 <para> 577 Now that we know what buffers and triggers are let's see how they 578 work together. 579 </para> 580 <sect2 id="iiotrigbufsetup"> <title> IIO triggered buffer setup</title> 581 !Edrivers/iio/buffer/industrialio-triggered-buffer.c 582 !Finclude/linux/iio/iio.h iio_buffer_setup_ops 583 584 585 <para> 586 A typical triggered buffer setup looks like this: 587 <programlisting> 588 const struct iio_buffer_setup_ops sensor_buffer_setup_ops = { 589 .preenable = sensor_buffer_preenable, 590 .postenable = sensor_buffer_postenable, 591 .postdisable = sensor_buffer_postdisable, 592 .predisable = sensor_buffer_predisable, 593 }; 594 595 irqreturn_t sensor_iio_pollfunc(int irq, void *p) 596 { 597 pf->timestamp = iio_get_time_ns((struct indio_dev *)p); 598 return IRQ_WAKE_THREAD; 599 } 600 601 irqreturn_t sensor_trigger_handler(int irq, void *p) 602 { 603 u16 buf[8]; 604 int i = 0; 605 606 /* read data for each active channel */ 607 for_each_set_bit(bit, active_scan_mask, masklength) 608 buf[i++] = sensor_get_data(bit) 609 610 iio_push_to_buffers_with_timestamp(indio_dev, buf, timestamp); 611 612 iio_trigger_notify_done(trigger); 613 return IRQ_HANDLED; 614 } 615 616 /* setup triggered buffer, usually in probe function */ 617 iio_triggered_buffer_setup(indio_dev, sensor_iio_polfunc, 618 sensor_trigger_handler, 619 sensor_buffer_setup_ops); 620 </programlisting> 621 </para> 622 The important things to notice here are: 623 <itemizedlist> 624 <listitem><function> iio_buffer_setup_ops</function>, the buffer setup 625 functions to be called at predefined points in the buffer configuration 626 sequence (e.g. before enable, after disable). If not specified, the 627 IIO core uses the default <type>iio_triggered_buffer_setup_ops</type>. 628 </listitem> 629 <listitem><function>sensor_iio_pollfunc</function>, the function that 630 will be used as top half of poll function. It should do as little 631 processing as possible, because it runs in interrupt context. The most 632 common operation is recording of the current timestamp and for this reason 633 one can use the IIO core defined <function>iio_pollfunc_store_time 634 </function> function. 635 </listitem> 636 <listitem><function>sensor_trigger_handler</function>, the function that 637 will be used as bottom half of the poll function. This runs in the 638 context of a kernel thread and all the processing takes place here. 639 It usually reads data from the device and stores it in the internal 640 buffer together with the timestamp recorded in the top half. 641 </listitem> 642 </itemizedlist> 643 </sect2> 644 </sect1> 645 </chapter> 646 <chapter id='iioresources'> 647 <title> Resources </title> 648 IIO core may change during time so the best documentation to read is the 649 source code. There are several locations where you should look: 650 <itemizedlist> 651 <listitem> 652 <filename>drivers/iio/</filename>, contains the IIO core plus 653 and directories for each sensor type (e.g. accel, magnetometer, 654 etc.) 655 </listitem> 656 <listitem> 657 <filename>include/linux/iio/</filename>, contains the header 658 files, nice to read for the internal kernel interfaces. 659 </listitem> 660 <listitem> 661 <filename>include/uapi/linux/iio/</filename>, contains files to be 662 used by user space applications. 663 </listitem> 664 <listitem> 665 <filename>tools/iio/</filename>, contains tools for rapidly 666 testing buffers, events and device creation. 667 </listitem> 668 <listitem> 669 <filename>drivers/staging/iio/</filename>, contains code for some 670 drivers or experimental features that are not yet mature enough 671 to be moved out. 672 </listitem> 673 </itemizedlist> 674 <para> 675 Besides the code, there are some good online documentation sources: 676 <itemizedlist> 677 <listitem> 678 <ulink url="http://marc.info/?l=linux-iio"> Industrial I/O mailing 679 list </ulink> 680 </listitem> 681 <listitem> 682 <ulink url="http://wiki.analog.com/software/linux/docs/iio/iio"> 683 Analog Device IIO wiki page </ulink> 684 </listitem> 685 <listitem> 686 <ulink url="https://fosdem.org/2015/schedule/event/iiosdr/"> 687 Using the Linux IIO framework for SDR, Lars-Peter Clausen's 688 presentation at FOSDEM </ulink> 689 </listitem> 690 </itemizedlist> 691 </para> 692 </chapter> 693 </book> 694 695 <!-- 696 vim: softtabstop=2:shiftwidth=2:expandtab:textwidth=72 697 -->