Lines Matching +full:pcm +full:- +full:interface +full:- +full:rate
11 Architecture) <http://www.alsa-project.org/>`__ driver. The document
19 low-level driver implementation details. It only describes the standard
26 -------
56 --------------
60 sub-directories contain different modules and are dependent upon the
66 The code for OSS PCM and mixer emulation modules is stored in this
74 This directory and its sub-directories are for the ALSA sequencer. This
76 as snd-seq-midi, snd-seq-virmidi, etc. They are compiled only when
85 -----------------
88 to be exported to user-space, or included by several files in different
94 -----------------
97 architectures. They are hence supposed not to be architecture-specific.
98 For example, the dummy PCM driver and the serial MIDI driver are found
99 in this directory. In the sub-directories, there is code for components
105 The MPU401 and MPU401-UART modules are stored here.
110 The OPL3 and OPL4 FM-synth stuff is found here.
113 -------------
122 ---------------
124 This contains the synth middle-level modules.
127 ``synth/emux`` sub-directory.
130 -------------
132 This directory and its sub-directories hold the top-level card modules
137 their own sub-directory (e.g. emu10k1, ice1712).
140 -------------
142 This directory and its sub-directories hold the top-level card modules
146 -------------------------------
148 They are used for top-level card modules which are specific to one of
152 -------------
154 This directory contains the USB-audio driver.
155 The USB MIDI driver is integrated in the usb-audio driver.
158 ----------------
165 -------------
171 -------------
182 -------
186 - define the PCI ID table (see the section `PCI Entries`_).
188 - create ``probe`` callback.
190 - create ``remove`` callback.
192 - create a struct pci_driver structure
195 - create an ``init`` function just calling the
199 - create an ``exit`` function to call the
203 -----------------
224 /* definition of the chip-specific record */
232 /* chip-specific destructor
240 /* component-destructor
245 return snd_mychip_free(device->device_data);
248 /* chip-specific constructor
268 /* allocate a chip-specific data with zero filled */
271 return -ENOMEM;
273 chip->card = card;
290 /* constructor -- see "Driver Constructor" sub-section */
301 return -ENODEV;
304 return -ENOENT;
308 err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
319 strcpy(card->driver, "My Chip");
320 strcpy(card->shortname, "My Own Chip 123");
321 sprintf(card->longname, "%s at 0x%lx irq %i",
322 card->shortname, chip->port, chip->irq);
342 /* destructor -- see the "Destructor" sub-section */
351 ------------------
354 ``probe`` callback and other component-constructors which are called
368 return -ENODEV;
371 return -ENOENT;
390 err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
428 strcpy(card->driver, "My Chip");
429 strcpy(card->shortname, "My Own Chip 123");
430 sprintf(card->longname, "%s at 0x%lx irq %i",
431 card->shortname, chip->port, chip->irq);
434 by alsa-lib's configurator, so keep it simple but unique. Even the
444 Here you define the basic components such as `PCM <PCM Interface_>`__,
446 `MPU-401 <MIDI (MPU401-UART) Interface_>`__), and other interfaces.
472 remove callback and power-management callbacks, too.
475 ----------
493 ------------
513 The ALSA interfaces like the PCM and control APIs are defined in other
521 -------------
526 list of devices (components) on the soundcard, such as PCM, mixers,
529 the power-management states and hotplug disconnections. The component
538 err = snd_card_new(&pci->dev, index, id, module, extra_size, &card);
542 card-index number, the id string, the module pointer (usually
543 ``THIS_MODULE``), the size of extra-data space, and the pointer to
545 card->private_data for the chip-specific data. Note that these data are
549 device. For PCI devices, typically ``&pci->`` is passed there.
552 ----------
557 can be a PCM instance, a control interface, a raw MIDI interface, etc.
565 This takes the card pointer, the device-level (``SNDRV_DEV_XXX``), the
566 data pointer, and the callback pointers (``&ops``). The device-level
568 de-registration. For most components, the device-level is already
569 defined. For a user-defined component, you can use
577 Each pre-defined ALSA component such as AC97 and PCM calls
585 example will show an implementation of chip-specific data.
587 Chip-Specific Data
588 ------------------
590 Chip-specific information, e.g. the I/O port address, its resource
591 pointer, or the irq number, is stored in the chip-specific record::
603 As mentioned above, you can pass the extra-data-length to the 5th
606 err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
615 struct mychip *chip = card->private_data;
628 err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
645 chip->card = card;
648 low-level device with a specified ``ops``::
656 :c:func:`snd_mychip_dev_free()` is the device-destructor
661 return snd_mychip_free(device->device_data);
674 ------------------------
695 -----------------
697 In this section, we'll complete the chip-specific constructor,
714 if (chip->irq >= 0)
715 free_irq(chip->irq, chip);
717 pci_release_regions(chip->pci);
719 pci_disable_device(chip->pci);
725 /* chip-specific constructor */
747 return -ENXIO;
753 return -ENOMEM;
757 chip->card = card;
758 chip->pci = pci;
759 chip->irq = -1;
768 chip->port = pci_resource_start(pci, 0);
769 if (request_irq(pci->irq, snd_mychip_interrupt,
771 printk(KERN_ERR "cannot grab irq %d\n", pci->irq);
773 return -EBUSY;
775 chip->irq = pci->irq;
776 card->sync_irq = chip->irq;
826 ------------
847 return -ENXIO;
852 -------------------
873 this number to -1 before actual allocation, since irq 0 is valid. The
886 chip->port = pci_resource_start(pci, 0);
889 The returned value, ``chip->res_port``, is allocated via
896 if (request_irq(pci->irq, snd_mychip_interrupt,
898 printk(KERN_ERR "cannot grab irq %d\n", pci->irq);
900 return -EBUSY;
902 chip->irq = pci->irq;
905 defined `later <PCM Interrupt Handler_>`__. Note that
906 ``chip->irq`` should be defined only when :c:func:`request_irq()`
913 passed to the interrupt handler. Usually, the chip-specific record is
927 After requesting the IRQ, you can passed it to ``card->sync_irq``
930 card->irq = chip->irq;
932 This allows the PCM core to automatically call
941 To release the resources, the “check-and-release” method is a safer way.
944 if (chip->irq >= 0)
945 free_irq(chip->irq, chip);
948 ``chip->irq`` with a negative value (e.g. -1), so that you can check
958 pci_release_regions(chip->pci);
964 chip->res_port, the release procedure looks like::
966 release_and_free_resource(chip->res_port);
971 And finally, release the chip-specific record::
981 When the chip-data is assigned to the card using
985 have to stop PCMs, etc. explicitly, but just call low-level hardware
988 The management of a memory-mapped region is almost as same as the
1004 chip->iobase_phys = pci_resource_start(pci, 0);
1005 chip->iobase_virt = ioremap(chip->iobase_phys,
1013 if (chip->iobase_virt)
1014 iounmap(chip->iobase_virt);
1016 pci_release_regions(chip->pci);
1028 chip->iobase_virt = pci_iomap(pci, 0, 0);
1034 -----------
1059 all-zero entry.
1095 PCM Interface
1099 -------
1101 The PCM middle layer of ALSA is quite powerful and it is only necessary
1102 for each driver to implement the low-level functions to access its
1105 To access the PCM layer, you need to include ``<sound/pcm.h>``
1109 Each card device can have up to four PCM instances. A PCM instance
1110 corresponds to a PCM device file. The limitation of number of instances
1112 Once 64bit device numbers are used, we'll have more PCM instances
1115 A PCM instance consists of PCM playback and capture streams, and each
1116 PCM stream consists of one or more PCM substreams. Some soundcards
1117 support multiple playback functions. For example, emu10k1 has a PCM
1123 PCM middle layer will take care of such work.
1126 -----------------
1129 shows only the skeleton, how to build up the PCM interfaces::
1131 #include <sound/pcm.h>
1176 struct snd_pcm_runtime *runtime = substream->runtime;
1178 runtime->hw = snd_mychip_playback_hw;
1179 /* more hardware-initialization will be done here */
1188 /* the hardware-specific codes will be here */
1198 struct snd_pcm_runtime *runtime = substream->runtime;
1200 runtime->hw = snd_mychip_capture_hw;
1201 /* more hardware-initialization will be done here */
1210 /* the hardware-specific codes will be here */
1219 /* the hardware-specific codes will be here */
1227 /* the hardware-specific codes will be here */
1236 struct snd_pcm_runtime *runtime = substream->runtime;
1241 mychip_set_sample_format(chip, runtime->format);
1242 mychip_set_sample_rate(chip, runtime->rate);
1243 mychip_set_channels(chip, runtime->channels);
1244 mychip_set_dma_setup(chip, runtime->dma_addr,
1245 chip->buffer_size,
1246 chip->period_size);
1256 /* do something to start the PCM engine */
1260 /* do something to stop the PCM engine */
1264 return -EINVAL;
1306 /* create a pcm device */
1309 struct snd_pcm *pcm;
1312 err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm);
1315 pcm->private_data = chip;
1316 strcpy(pcm->name, "My Chip");
1317 chip->pcm = pcm;
1319 snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
1321 snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
1323 /* pre-allocation of buffers */
1325 snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV,
1326 &chip->pci->dev,
1332 PCM Constructor
1333 ---------------
1335 A PCM instance is allocated by the :c:func:`snd_pcm_new()`
1336 function. It would be better to create a constructor for the PCM, namely::
1340 struct snd_pcm *pcm;
1343 err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm);
1346 pcm->private_data = chip;
1347 strcpy(pcm->name, "My Chip");
1348 chip->pcm = pcm;
1354 first argument is the card pointer to which this PCM is assigned, and
1358 PCM. It begins from zero. If you create more than one PCM instances,
1360 1`` for the second PCM device.
1374 int index = substream->number;
1377 After the PCM is created, you need to set operators for each PCM stream::
1379 snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
1381 snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
1398 After setting the operators, you probably will want to pre-allocate the
1402 snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV,
1403 &chip->pci->dev,
1410 Additionally, you can set some extra information for this PCM in
1411 ``pcm->info_flags``. The available values are defined as
1414 half-duplex, specify it like this::
1416 pcm->info_flags = SNDRV_PCM_INFO_HALF_DUPLEX;
1420 -----------------------
1422 The destructor for a PCM instance is not always necessary. Since the PCM
1428 destructor function to ``pcm->private_free``::
1430 static void mychip_pcm_free(struct snd_pcm *pcm)
1432 struct mychip *chip = snd_pcm_chip(pcm);
1434 kfree(chip->my_private_pcm_data);
1441 struct snd_pcm *pcm;
1444 chip->my_private_pcm_data = kmalloc(...);
1446 pcm->private_data = chip;
1447 pcm->private_free = mychip_pcm_free;
1453 Runtime Pointer - The Chest of PCM Information
1454 ----------------------------------------------
1456 When the PCM substream is opened, a PCM runtime instance is allocated
1458 ``substream->runtime``. This runtime pointer holds most information you
1459 need to control the PCM: a copy of hw_params and sw_params
1462 The definition of runtime instance is found in ``<sound/pcm.h>``. Here
1466 /* -- Status -- */
1474 /* -- HW params -- */
1478 unsigned int rate; /* rate in Hz */
1492 /* -- SW params -- */
1501 snd_pcm_uframes_t stop_threshold; /* - stop playback */
1502 snd_pcm_uframes_t silence_threshold; /* - pre-fill buffer with silence */
1503 snd_pcm_uframes_t silence_size; /* max size of silence pre-fill; when >= boundary,
1507 /* internal data of auto-silencer */
1513 /* -- mmap -- */
1518 /* -- locking / scheduling -- */
1524 /* -- private section -- */
1528 /* -- hardware description -- */
1532 /* -- timer -- */
1535 /* -- DMA -- */
1543 /* -- OSS things -- */
1550 records are supposed to be read-only. Only the PCM middle-layer changes
1563 in the `PCM open callback`_. Note that the runtime instance holds a copy of
1566 (``runtime->hw``) as you need. For example, if the maximum number of
1570 struct snd_pcm_runtime *runtime = substream->runtime;
1572 runtime->hw = snd_mychip_playback_hw; /* common definition */
1573 if (chip->model == VERY_OLD_ONE)
1574 runtime->hw.channels_max = 1;
1596 - The ``info`` field contains the type and capabilities of this
1597 PCM. The bit flags are defined in ``<sound/asound.h>`` as
1602 interleaved or the non-interleaved formats, the
1612 ``SNDRV_PCM_INFO_RESUME``. The ``PAUSE`` bit means that the PCM
1614 the PCM supports the full “suspend/resume” operation. If the
1620 When the PCM substreams can be synchronized (typically,
1623 need to check the linked-list of PCM substreams in the trigger
1626 - The ``formats`` field contains the bit-flags of supported formats
1629 little-endian format is specified.
1631 - The ``rates`` field contains the bit-flags of supported rates
1633 pass the ``CONTINUOUS`` bit additionally. The pre-defined rate bits
1638 - ``rate_min`` and ``rate_max`` define the minimum and maximum sample
1639 rate. This should correspond somehow to ``rates`` bits.
1641 - ``channels_min`` and ``channels_max`` define, as you might have already
1644 - ``buffer_bytes_max`` defines the maximum buffer size in
1653 world. The period defines the point at which a PCM interrupt is
1661 - There is also a field ``fifo_size``. This specifies the size of the
1663 in the alsa-lib. So, you can ignore this field.
1665 PCM Configurations
1668 Ok, let's go back again to the PCM runtime records. The most
1669 frequently referred records in the runtime instance are the PCM
1670 configurations. The PCM configurations are stored in the runtime
1672 alsa-lib. There are many fields copied from hw_params and sw_params
1679 channels \* samples-size``. For conversion between frames and bytes,
1683 period_bytes = frames_to_bytes(runtime, runtime->period_size);
1715 The running status can be referred via ``runtime->status``. This is
1718 DMA hardware pointer via ``runtime->status->hw_ptr``.
1720 The DMA application pointer can be referred via ``runtime->control``,
1728 ``runtime->private_data``. Usually, this is done in the `PCM open
1729 callback`_. Don't mix this with ``pcm->private_data``. The
1730 ``pcm->private_data`` usually points to the chip instance assigned
1731 statically at creation time of the PCM device, while
1732 ``runtime->private_data``
1733 points to a dynamic data structure created in the PCM open
1741 substream->runtime->private_data = data;
1749 ---------
1751 OK, now let me give details about each PCM callback (``ops``). In
1753 error number such as ``-EINVAL``. To choose an appropriate error
1767 The macro reads ``substream->private_data``, which is a copy of
1768 ``pcm->private_data``. You can override the former if you need to
1769 assign different data records per PCM substream. For example, the
1771 capture directions, because it uses two different codecs (SB- and
1772 AD-compatible) for different directions.
1774 PCM open callback
1781 This is called when a PCM substream is opened.
1783 At least, here you have to initialize the ``runtime->hw``
1789 struct snd_pcm_runtime *runtime = substream->runtime;
1791 runtime->hw = snd_mychip_playback_hw;
1795 where ``snd_mychip_playback_hw`` is the pre-defined hardware
1812 Obviously, this is called when a PCM substream is closed.
1814 Any private instance for a PCM substream allocated in the ``open``
1820 kfree(substream->runtime->private_data);
1827 This is used for any special call to PCM ioctls. But usually you can
1828 leave it NULL, then the PCM core calls the generic ioctl callback
1843 size, the format, etc. are defined for the PCM substream.
1859 DMA buffers have been pre-allocated. See the section `Buffer Types`_
1871 Another note is that this callback is non-atomic (schedulable) by
1873 because the ``trigger`` callback is atomic (non-schedulable). That is,
1874 mutexes or any schedule-related functions are not available in the
1892 When you have chosen managed buffer allocation mode for the PCM
1893 substream, the allocated PCM buffer will be automatically released
1896 pre-allocated pool, you can use the standard API function
1908 This callback is called when the PCM is “prepared”. You can set the
1909 format type, sample rate, etc. here. The difference from ``hw_params``
1914 Note that this callback is non-atomic. You can use
1915 schedule-related functions safely in this callback.
1918 the runtime record, ``substream->runtime``. For example, to get the
1919 current rate, format or channels, access to ``runtime->rate``,
1920 ``runtime->format`` or ``runtime->channels``, respectively. The
1922 ``runtime->dma_area``. The buffer and period sizes are in
1923 ``runtime->buffer_size`` and ``runtime->period_size``, respectively.
1935 This is called when the PCM is started, stopped or paused.
1938 defined in ``<sound/pcm.h>``. At least, the ``START``
1943 /* do something to start the PCM engine */
1946 /* do something to stop the PCM engine */
1949 return -EINVAL;
1952 When the PCM supports the pause operation (given in the info field of
1954 must be handled here, too. The former is the command to pause the PCM,
1955 and the latter to restart the PCM again.
1957 When the PCM supports the suspend/resume operation, regardless of full
1960 power-management status is changed. Obviously, the ``SUSPEND`` and
1961 ``RESUME`` commands suspend and resume the PCM substream, and usually,
1979 the PCM core stops the stream, before it changes the stream state via
1989 While keeping the ``sync_stop`` PCM callback NULL, the driver can set
1990 the ``card->sync_irq`` field to the returned interrupt number after
1991 requesting an IRQ, instead. Then PCM core will call
1995 to clear ``card->sync_irq``, as the card itself is being released.
1997 ``card->sync_irq`` in the driver code unless the driver re-acquires
1998 the IRQ. When the driver frees and re-acquires the IRQ dynamically
1999 (e.g. for suspend/resume), it needs to clear and re-set
2000 ``card->sync_irq`` again appropriately.
2009 This callback is called when the PCM middle layer inquires the current
2011 frames, ranging from 0 to ``buffer_size - 1``.
2013 This is usually called from the buffer-update routine in the PCM
2015 is called by the interrupt routine. Then the PCM middle layer updates
2029 buffer is non-contiguous on both physical and virtual memory spaces,
2032 If these two callbacks are defined, copy and set-silence operations
2041 emu10k1-fx and cs46xx need to track the current ``appl_ptr`` for the
2045 return value is ``-EPIPE``, PCM core treats that as a buffer XRUN,
2056 You need no special callback for the standard SG-buffer or vmalloc-
2063 When defined, the PCM core calls this callback when a page is
2064 memory-mapped, instead of using the standard helper.
2066 device-specific issues), implement everything here as you like.
2069 PCM Interrupt Handler
2070 ---------------------
2072 The remainder of the PCM stuff is the PCM interrupt handler. The role
2073 of the PCM
2075 and to tell the PCM middle layer when the buffer position goes across
2095 in other PCM callbacks, too, then you have to release the lock before
2097 :c:func:`snd_pcm_period_elapsed()` calls other PCM callbacks
2106 spin_lock(&chip->lock);
2110 spin_unlock(&chip->lock);
2111 snd_pcm_period_elapsed(chip->substream);
2112 spin_lock(&chip->lock);
2116 spin_unlock(&chip->lock);
2121 can notify the XRUN status to the PCM core by calling
2123 the PCM state to ``SNDRV_PCM_STATE_XRUN``. Note that it must be called
2124 outside the PCM stream lock, hence it can't be called from the atomic
2132 boundary but issues timer interrupts at a fixed timer rate (e.g. es1968
2144 spin_lock(&chip->lock);
2153 if (last_ptr < chip->last_ptr)
2154 size = runtime->buffer_size + last_ptr
2155 - chip->last_ptr;
2157 size = last_ptr - chip->last_ptr;
2159 chip->last_ptr = last_ptr;
2161 chip->size += size;
2163 if (chip->size >= runtime->period_size) {
2165 chip->size %= runtime->period_size;
2167 spin_unlock(&chip->lock);
2169 spin_lock(&chip->lock);
2174 spin_unlock(&chip->lock);
2185 once. And the PCM layer will check the current hardware pointer and
2189 ---------
2193 usually avoided via spin-locks, mutexes or semaphores. In general, if a
2200 As already seen, some PCM callbacks are atomic and some are not. For
2201 example, the ``hw_params`` callback is non-atomic, while the ``trigger``
2203 spinlock held by the PCM middle layer, the PCM stream lock. Please
2216 However, it is possible to request all PCM operations to be non-atomic.
2218 non-atomic contexts. For example, the function
2221 interrupt handler, this call can be in non-atomic context, too. In such
2224 in the PCM core instead of spin and rwlocks, so that you can call all PCM
2225 functions safely in a non-atomic
2231 variant that can be called inside the PCM stream lock
2236 -----------
2257 err = snd_pcm_hw_constraint_list(substream->runtime, 0,
2265 There are many different constraints. Look at ``sound/pcm.h`` for a
2281 if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) {
2292 snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
2294 SNDRV_PCM_HW_PARAM_FORMAT, -1);
2296 The rule function is called when an application sets the PCM format, and
2310 if (c->min < 2) {
2320 snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT,
2322 SNDRV_PCM_HW_PARAM_CHANNELS, -1);
2325 with the period size. By default, ALSA PCM core doesn't enforce the
2335 snd_pcm_hw_constraint_integer(substream->runtime,
2342 preferred PCM configuration, and there are relevant helpers.
2346 Control Interface
2350 -------
2352 The control interface is used widely for many switches, sliders, etc.
2353 which are accessed from user-space. Its most important use is the mixer
2354 interface. In other words, since ALSA 0.9.x, all the mixer stuff is
2357 ALSA has a well-defined AC97 control module. If your chip supports only
2364 ----------------------
2373 .name = "PCM Playback Switch",
2387 card, use ``HWDEP``, ``PCM``, ``RAWMIDI``, ``TIMER``, or ``SEQUENCER``,
2393 its name. There are pre-defined standard control names. The details
2420 -------------
2426 string such as “Master”, “PCM”, “CD” and “Line”. There are many
2427 pre-defined sources.
2437 The example of control names are, thus, “Master Capture Switch” or “PCM
2450 Tone-controls
2453 tone-control switch and volumes are specified like “Tone Control - XXX”,
2454 e.g. “Tone Control - Switch”, “Tone Control - Bass”, “Tone Control -
2460 3D-control switches and volumes are specified like “3D Control - XXX”,
2461 e.g. “3D Control - Switch”, “3D Control - Center”, “3D Control - Space”.
2466 Mic-boost switch is set as “Mic Boost” or “Mic Boost (6dB)”.
2469 ``Documentation/sound/designs/control-names.rst``.
2472 ------------
2480 When the control is read-only, pass ``SNDRV_CTL_ELEM_ACCESS_READ``
2482 Similarly, when the control is write-only (although it's a rare case),
2492 setting the ``INACTIVE`` flag may be appropriate. For example, PCM
2493 controls should be inactive while no PCM device is open.
2498 -----------------
2512 uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN;
2513 uinfo->count = 1;
2514 uinfo->value.integer.min = 0;
2515 uinfo->value.integer.max = 1;
2537 uinfo->type = SNDRV_CTL_ELEM_TYPE_ENUMERATED;
2538 uinfo->count = 1;
2539 uinfo->value.enumerated.items = 4;
2540 if (uinfo->value.enumerated.item > 3)
2541 uinfo->value.enumerated.item = 3;
2542 strcpy(uinfo->value.enumerated.name,
2543 texts[uinfo->value.enumerated.item]);
2575 can be returned to user-space.
2583 ucontrol->value.integer.value[0] = get_some_value(chip);
2591 register offset, the bit-shift and the bit-mask. The ``private_value``
2601 int reg = kcontrol->private_value & 0xff;
2602 int shift = (kcontrol->private_value >> 16) & 0xff;
2603 int mask = (kcontrol->private_value >> 24) & 0xff;
2615 This callback is used to write a value coming from user-space.
2624 if (chip->current_value !=
2625 ucontrol->value.integer.value[0]) {
2627 ucontrol->value.integer.value[0]);
2645 All these three callbacks are not-atomic.
2648 -------------------
2661 and chip is the object pointer to be passed to kcontrol->private_data which
2669 -------------------
2676 This function takes the card pointer, the event-mask, and the control id
2677 pointer for the notification. The event-mask specifies the types of
2684 --------
2692 static DECLARE_TLV_DB_SCALE(db_scale_my_control, -4050, 150, 0);
2723 -------
2725 The ALSA AC97 codec layer is a well-defined one, and you don't have to
2726 write much code to control it. Only low-level control routines are
2730 -----------------
2743 struct mychip *chip = ac97->private_data;
2752 struct mychip *chip = ac97->private_data;
2767 err = snd_ac97_bus(chip->card, 0, &ops, NULL, &bus);
2772 return snd_ac97_mixer(bus, &ac97, &chip->ac97);
2777 ----------------
2800 snd_ac97_mixer(bus, &ac97, &chip->ac97);
2802 where chip->ac97 is a pointer to a newly created ``ac97_t``
2811 --------------
2815 hardware low-level codes.
2823 struct mychip *chip = ac97->private_data;
2828 Here, the chip can be cast from ``ac97->private_data``.
2837 These callbacks are non-atomic like the control API callbacks.
2852 --------------------------------
2879 Also, there is a function to change the sample rate (of a given register
2886 The following registers are available to set the rate:
2893 ----------------
2896 (to save a quartz!). In this case, change the field ``bus->clock`` to
2901 ----------
2903 The ALSA AC97 interface will create a proc file such as
2904 ``/proc/asound/card0/codec97#0/ac97#0-0`` and ``ac97#0-0+regs``. You
2909 ---------------
2916 callbacks for each codec or check ``ac97->num`` in the callback
2919 MIDI (MPU401-UART) Interface
2923 -------
2925 Many soundcards have built-in MIDI (MPU401-UART) interfaces. When the
2926 soundcard supports the standard MPU401-UART interface, most likely you
2927 can use the ALSA MPU401-UART API. The MPU401-UART API is defined in
2934 ----------------
2949 The 4th argument is the I/O port address. Many backward-compatible
2957 mpu401-uart layer will allocate the I/O ports by itself.
2972 If the MPU-401 interface shares its interrupt with the other logical
2981 need to cast ``rmidi->private_data`` to struct snd_mpu401 explicitly::
2984 mpu = rmidi->private_data;
2988 mpu->cport = my_own_control_port;
2993 -1 instead. For a MPU-401 device without an interrupt, a polling timer
2997 ----------------------
3012 snd_mpu401_uart_interrupt(irq, rmidi->private_data, regs);
3015 RawMIDI Interface
3019 --------
3021 The raw MIDI interface is used for hardware MIDI ports that can be
3031 -------------------
3037 err = snd_rawmidi_new(chip->card, "MyMIDI", 0, outs, ins, &rmidi);
3040 rmidi->private_data = chip;
3041 strcpy(rmidi->name, "My MIDI");
3042 rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT |
3084 &rmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT].substreams,
3086 sprintf(substream->name, "My MIDI Port %d", substream->number + 1);
3091 -----------------
3094 device can be accessed as ``substream->rmidi->private_data``.
3101 int index = substream->number;
3223 -------
3229 FM registers can be directly accessed through the direct-FM API, defined
3231 accessed through the Hardware-Dependent Device direct-FM extension API,
3233 OSS direct-FM compatible API in ``/dev/dmfmX`` device.
3249 driver, pass non-zero to the fifth argument (``integrated``). Otherwise,
3263 ``opl3->private_data`` field.
3279 The third argument is the index-offset for the sequencer client assigned
3280 to the OPL3 port. When there is an MPU401-UART, give 1 for here (UART
3283 Hardware-Dependent Devices
3284 --------------------------
3286 Some chips need user-space access for special controls or for loading
3288 (hardware-dependent) device. The hwdep API is defined in
3305 hw->private_data = p;
3306 hw->private_free = mydata_free;
3312 struct mydata *p = hw->private_data;
3320 hw->ops.open = mydata_open;
3321 hw->ops.ioctl = mydata_ioctl;
3322 hw->ops.release = mydata_release;
3327 ---------------
3330 interface. There is a macro to compose a name string for IEC958
3340 “IEC958 Playback Con Mask” is used to return the bit-mask for the IEC958
3342 returns the bitmask for professional mode. They are read-only controls.
3364 ------------
3368 allocation of physically-contiguous pages is done via the
3383 is called “pre-allocation”. As already written, you can call the
3384 following function at PCM instance construction time (in the case of PCI
3387 snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
3388 &pci->dev, size, max);
3390 where ``size`` is the byte size to be pre-allocated and ``max`` is
3397 (typically identical as ``card->dev``) to the third argument with
3401 bus can be pre-allocated with ``SNDRV_DMA_TYPE_CONTINUOUS`` type.
3409 For the scatter-gather buffers, use ``SNDRV_DMA_TYPE_DEV_SG`` with the
3410 device pointer (see the `Non-Contiguous Buffers`_ section).
3412 Once the buffer is pre-allocated, you can use the allocator in the
3417 Note that you have to pre-allocate to use this function.
3424 snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV,
3425 &pci->dev, size, max);
3428 The difference in the managed mode is that PCM core will call
3430 the PCM ``hw_params`` callback, and call :c:func:`snd_pcm_lib_free_pages()`
3431 after the PCM ``hw_free`` callback automatically. So the driver
3437 -------------------------
3450 mmapped. The examples are GUS's GF1 PCM or emu8000's wavetable PCM.
3457 Another case is when the chip uses a PCI memory-map region for the
3459 on certain architectures like the Intel one. In non-mmap mode, the data
3467 interleaved or non-interleaved samples. The ``copy`` callback is
3490 offset (``pos``) in the hardware buffer. When coded like memcpy-like
3508 it easier to unify both the interleaved and non-interleaved cases, as
3511 In the case of non-interleaved samples, the implementation will be a bit
3517 the given user-space buffer, but only for the given channel. For
3536 silent-data is 0), and the implementation using a memset-like function
3541 In the case of non-interleaved samples, again, the implementation
3545 Non-Contiguous Buffers
3546 ----------------------
3549 descriptors as in via82xx, you can use scatter-gather (SG) DMA. ALSA
3550 provides an interface for handling SG-buffers. The API is provided in
3551 ``<sound/pcm.h>``.
3553 For creating the SG-buffer handler, call
3556 ``SNDRV_DMA_TYPE_DEV_SG`` in the PCM constructor like for other PCI
3557 pre-allocations. You need to pass ``&pci->dev``, where pci is
3560 snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV_SG,
3561 &pci->dev, size, max);
3564 ``substream->dma_private`` in turn. You can cast the pointer like::
3566 struct snd_sg_buf *sgbuf = (struct snd_sg_buf *)substream->dma_private;
3568 Then in the :c:func:`snd_pcm_lib_malloc_pages()` call, the common SG-buffer
3569 handler will allocate the non-contiguous kernel pages of the given size
3571 is addressed via runtime->dma_area. The physical address
3572 (``runtime->dma_addr``) is set to zero, because the buffer is
3573 physically non-contiguous. The physical address table is set up in
3574 ``sgbuf->table``. You can get the physical address at a certain offset
3577 If you need to release the SG-buffer data explicitly, call the
3581 ------------------
3589 snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_VMALLOC,
3598 we don't need to pre-allocate the buffers like other continuous
3601 Proc Interface
3604 ALSA provides an easy interface for procfs. The proc files are very
3612 int err = snd_card_proc_new(card, "my-file", &entry);
3615 created. The above example will create a file ``my-file`` under the
3616 card directory, e.g. ``/proc/asound/card0/my-file``.
3624 proc file for read only. To use this proc file as a read-only text file
3625 as-is, set the read callback with private data via
3645 struct my_chip *chip = entry->private_data;
3648 snd_iprintf(buffer, "Port = %ld\n", chip->port);
3655 entry->mode = S_IFREG | S_IRUGO | S_IWUSR;
3659 entry->c.text.write = my_proc_write;
3666 For a raw-data proc-file, set the attributes as follows::
3672 entry->content = SNDRV_INFO_CONTENT_DATA;
3673 entry->private_data = chip;
3674 entry->c.ops = &my_file_io_ops;
3675 entry->size = 4096;
3676 entry->mode = S_IFREG | S_IRUGO;
3682 You need to use a low-level I/O functions such as
3694 return -EFAULT;
3707 to add power-management code to the driver. The additional code for
3708 power-management should be ifdef-ed with ``CONFIG_PM``, or annotated
3713 ``SNDRV_PCM_INFO_RESUME`` flag in the PCM info field. Usually, this is
3723 don't set the ``SNDRV_PCM_INFO_RESUME`` info flag to the PCM.
3768 struct mychip *chip = card->private_data;
3772 snd_ac97_suspend(chip->ac97);
3785 2. Re-initialize the chip.
3802 struct mychip *chip = card->private_data;
3808 snd_ac97_resume(chip->ac97);
3816 Note that, at the time this callback gets called, the PCM stream has
3833 err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
3838 card->private_data = chip;
3853 err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
3856 chip = card->private_data;
3920 Device-Managed Resources
3926 the (device-)managed resources aka devres or devm family. For
3930 ALSA core provides also the device-managed helper, namely,
3941 so be careful to put the hardware clean-up procedure in
3947 Another thing to be remarked is that you should use device-managed
3957 -------
3964 module name would be snd-xyz. The new driver is usually put into the
3965 alsa-driver tree, ``sound/pci`` directory in the case of PCI
3973 --------------------------------
3979 snd-xyz-y := xyz.o
3980 obj-$(CONFIG_SND_XYZ) += snd-xyz.o
3993 the module will be called snd-xyz.
3995 The line ``select SND_PCM`` specifies that the driver xyz supports PCM.
4002 PCM includes TIMER, MPU401_UART includes RAWMIDI, AC97_CODEC
4003 includes PCM, and OPL3_LIB includes HWDEP. You don't need to give
4009 ---------------------------------
4011 Suppose that the driver snd-xyz have several source files. They are
4017 obj-$(CONFIG_SND) += sound/pci/xyz/
4022 snd-xyz-y := xyz.o abc.o def.o
4023 obj-$(CONFIG_SND_XYZ) += snd-xyz.o
4034 -------------------
4043 ----------------------
4048 return -EINVAL;
4051 ``CONFIG_SND_DEBUG``, is set, if the expression is non-zero, it shows
4061 Kevin Conder reformatted the original plain-text to the DocBook format.