In this patch series, I added a description about control interface handling and how control interfaces are identified.
In addition, I added/improved Doxygen documentation for the snd_ctl_card_info_t type and related corresponding functions, e.g. snd_ctl_card_info(). I also documented other card-related like snd_card_next().
Along the way I did minor documentation improvements.
Signed-off-by: Tanjeff-N. Moos tanjeff@cccmz.de --- include/control.h | 40 +++++++++- src/control/cards.c | 56 +++++++++----- src/control/control.c | 175 +++++++++++++++++++++++++++++++----------- 3 files changed, 202 insertions(+), 69 deletions(-)
diff --git a/include/control.h b/include/control.h index 8766f440..e1a0da47 100644 --- a/include/control.h +++ b/include/control.h @@ -50,7 +50,32 @@ typedef struct snd_aes_iec958 { unsigned char dig_subframe[4]; /**< AES/IEC958 subframe bits */ } snd_aes_iec958_t;
-/** CTL card info container */ +/** \brief CTL card info container. + * + * This type contains meta information about a sound card, such as the index, + * name, longname, etc. + * + * \par Memory management + * + * Before using a snd_ctl_card_info_t object, it must be allocated using + * snd_ctl_card_info_alloca() or snd_ctl_card_info_malloc(). When using the + * latter, it must be freed again using snd_ctl_card_info_free(). + * + * A card info object can be zeroed out using snd_ctl_card_info_clear(). + * + * A card info object can be copied to another one using + * snd_ctl_card_info_copy(). + * + * \par Obtaining the Information + * + * To obtain the card information, it must first be opened using + * snd_ctl_open(), and a snd_ctl_card_info_t container must be + * allocated. Then, the information can be read using + * snd_ctl_card_info_get_card(). + * + * Thereafter, the card properties can be read using the + * snd_ctl_card_info_get_*() functions. + */ typedef struct _snd_ctl_card_info snd_ctl_card_info_t;
/** CTL element identifier container */ @@ -438,11 +463,20 @@ void snd_ctl_elem_id_set_name(snd_ctl_elem_id_t *obj, const char *val); void snd_ctl_elem_id_set_index(snd_ctl_elem_id_t *obj, unsigned int val);
size_t snd_ctl_card_info_sizeof(void); + /** \hideinitializer - * \brief allocate an invalid #snd_ctl_card_info_t using standard alloca - * \param ptr returned pointer + * \brief Allocate an invalid #snd_ctl_card_info_t on the stack. + * + * Allocate space for a card info object on the stack. The allocated + * memory need not be freed, because it is on the stack. + * + * See snd_ctl_card_info_t for details. + * + * \param ptr Pointer to a snd_ctl_elem_value_t pointer. The address + * of the allocated space will returned here. */ #define snd_ctl_card_info_alloca(ptr) __snd_alloca(ptr, snd_ctl_card_info) + int snd_ctl_card_info_malloc(snd_ctl_card_info_t **ptr); void snd_ctl_card_info_free(snd_ctl_card_info_t *obj); void snd_ctl_card_info_clear(snd_ctl_card_info_t *obj); diff --git a/src/control/cards.c b/src/control/cards.c index e57457c2..8226c42d 100644 --- a/src/control/cards.c +++ b/src/control/cards.c @@ -77,8 +77,8 @@ static int snd_card_load1(int card)
/** * \brief Try to load the driver for a card. - * \param card Card number. - * \return 1 if driver is present, zero if driver is not present + * \param card Card index. + * \return 1 if driver is present, zero if driver is not present. */ int snd_card_load(int card) { @@ -86,14 +86,24 @@ int snd_card_load(int card) }
/** - * \brief Try to determine the next card. - * \param rcard pointer to card number - * \result zero if success, otherwise a negative error code + * \brief Iterate over physical sound cards. + * + * This function takes the index of a physical sound card and sets it to the + * index of the next card. If index is -1, it is set to the index of the first + * card. After the last card, the index is set to -1. + * + * For example, if you have 2 sound cards (with index 0 and 1), the index will + * be modified as follows: + * + * - -1 --> 0 + * - 0 --> 1 + * - 1 --> -1 + * + * This does not work for virtual sound cards. * - * Tries to determine the next card from given card number. - * If card number is -1, then the first available card is - * returned. If the result card number is -1, no more cards - * are available. + * \param rcard Index of current card. The index of the next card is stored + * here. + * \result zero if success, otherwise a negative error code. */ int snd_card_next(int *rcard) { @@ -114,13 +124,18 @@ int snd_card_next(int *rcard) }
/** - * \brief Convert card string to an integer value. - * \param string String containing card identifier - * \return zero if success, otherwise a negative error code + * \brief Convert a card string to the card index. * - * The accepted format is an integer value in ASCII representation - * or the card identifier (the id parameter for sound-card drivers). - * The control device name like /dev/snd/controlC0 is accepted, too. + * This works only for physical sound cards, not for virtual cards. + * + * \param string A string identifying the card. + * \return The index of the card. On error, a a negative error code + * is returned. + * + * The accepted formats for "string" are: + * - The index of the card (as listed in /proc/asound/cards), given as string + * - The ID of the card (as listed in /proc/asound/cards) + * - The control device name (like /dev/snd/controlC0) */ int snd_card_get_index(const char *string) { @@ -163,8 +178,9 @@ int snd_card_get_index(const char *string)
/** * \brief Obtain the card name. - * \param card Card number - * \param name Result - card name corresponding to card number + * + * \param card The index of the card. + * \param name Result - card name corresponding to card index. * \result zero if success, otherwise a negative error code * * The value returned in name is allocated with strdup and should be @@ -193,9 +209,9 @@ int snd_card_get_name(int card, char **name)
/** * \brief Obtain the card long name. - * \param card Card number - * \param name Result - card long name corresponding to card number - * \result zero if success, otherwise a negative error code + * \param card Index of the card. + * \param name Result - card long name corresponding to card index. + * \result Zero if success, otherwise a negative error code. * * The value returned in name is allocated with strdup and should be * freed when no longer used. diff --git a/src/control/control.c b/src/control/control.c index 08058c06..7abf8ee3 100644 --- a/src/control/control.c +++ b/src/control/control.c @@ -33,8 +33,50 @@ <P>Control interface is designed to access primitive controls. There is also an interface for notifying about control and structure changes.
+ \section control_general_overview General overview
+In Alsa, there are physical sound cards, such as USB headsets, and +virtual sound cards, such as "pulse", which represents the PulseAudio +Sound system. Each sound card offers a control interface, making its +settings (e.g. volume knobs) available. The complete list of available +control interfaces can be obtained using snd_device_name_hint(), +giving -1 as card index and "ctl" as interface type. Each returned +NAME hint identifies a control interface. + +Sound cards have an ID (a string), an index (an int, sometimes called +the "card number"), a name, a longname, a mixername and a "components" +property. The file /proc/asound/cards lists most of these properties +for physical sound cards. Virtual sound cards are not listed in that +file. The format is: + +\verbatim +index [ID ] Driver - name + longname +\endverbatim + +Note that the mixername and components are not listed. + + +\subsection control_cards_id Identifying and Opening Control Interfaces + +To work with a control interface, is must be opened first, using +snd_ctl_open(). This function takes the interface name. + +For physical sound cards, the control interface can be identified +using the string "hw:<index>" (e.g. `hw:2`). The NAME hint - which is +"hw:CARD=<ID>" - can also be used. Further, its device file (something +like `/dev/snd/controlC0`) is also acceptable. Either of them can be +given to snd_ctl_open(). + +For virtual sound cards, the NAME hint is given to snd_ctl_open(). + +The functions snd_card_get_index(), snd_card_get_name() and +snd_card_get_longname() can be used to find an identifying property +when another one is already known. + +\section control_elements Elements + In ALSA control feature, each sound card can have control elements. The elements are managed according to below model.
@@ -65,7 +107,7 @@ are managed according to below model. of userspace applications and drivers in kernel.
-\section identifying_elements Identifying Elements +\subsection identifying_elements Identifying Elements
Each element has the following identifying properties:
@@ -84,7 +126,7 @@ rare). The numid can change on each boot. In case of an USB sound card, the numid can also change when it is reconnected.
-\section element_lists Element Lists +\subsection element_lists Element Lists
An element list can be used to obtain a list of all elements of the sound card. The list contains generic information (e.g. how many @@ -93,7 +135,7 @@ elements the card has), and the identifying properties of the elements element lists.
-\section working_with_elements Working with Elements +\subsection working_with_elements Working with Elements
It is possible to obtain information about an element using the snd_ctl_elem_info_*() functions. For enums, the allowed values can be @@ -108,7 +150,7 @@ actual values or settings. It is also possible to get and set the ID values (such as the numid or the name).
-\section element_sets Element Sets +\subsection element_sets Element Sets
The type of element set is one of integer, integer64, boolean, enumerators, bytes and IEC958 structure. This indicates the type of value for each member in @@ -328,10 +370,15 @@ int snd_ctl_subscribe_events(snd_ctl_t *ctl, int subscribe)
/** - * \brief Get card related information - * \param ctl CTL handle - * \param info Card info pointer - * \return 0 on success otherwise a negative error code + * \brief Get information about the sound card. + * + * Obtain information about the sound card previously opened using + * snd_ctl_open(). The object "info" must be allocated prior to calling this + * function. See snd_ctl_card_info_t for details. + * + * \param ctl The CTL handle. + * \param info The card information is stored here. + * \return 0 on success, otherwise a negative error code. */ int snd_ctl_card_info(snd_ctl_t *ctl, snd_ctl_card_info_t *info) { @@ -1477,11 +1524,13 @@ static int snd_ctl_open_noupdate(snd_ctl_t **ctlp, snd_config_t *root, const cha }
/** - * \brief Opens a CTL - * \param ctlp Returned CTL handle - * \param name ASCII identifier of the CTL handle - * \param mode Open mode (see #SND_CTL_NONBLOCK, #SND_CTL_ASYNC) - * \return 0 on success otherwise a negative error code + * \brief Opens a sound card. + * + * \param ctlp Returned CTL handle. + * \param name A string identifying the card (See \ref control_cards_id). + * \param mode Open mode (see #SND_CTL_NONBLOCK, #SND_CTL_ASYNC). + * + * \return 0 on success otherwise a negative error code. */ int snd_ctl_open(snd_ctl_t **ctlp, const char *name, int mode) { @@ -1925,8 +1974,8 @@ void snd_ctl_elem_id_set_index(snd_ctl_elem_id_t *obj, unsigned int val) }
/** - * \brief get size of #snd_ctl_card_info_t - * \return size in bytes + * \brief get size of #snd_ctl_card_info_t. + * \return Size in bytes. */ size_t snd_ctl_card_info_sizeof() { @@ -1934,9 +1983,16 @@ size_t snd_ctl_card_info_sizeof() }
/** - * \brief allocate an invalid #snd_ctl_card_info_t using standard malloc - * \param ptr returned pointer - * \return 0 on success otherwise negative error code + * \brief Allocate an invalid #snd_ctl_card_info_t on the heap. + * + * Allocate space for a card info object on the heap. The allocated memory + * must be freed using snd_ctl_card_info_free(). + * + * See snd_ctl_card_info_t for details. + * + * \param ptr Pointer to a snd_ctl_card_info_t pointer. The address + * of the allocated space will be returned here. + * \return 0 on success, otherwise a negative error code. */ int snd_ctl_card_info_malloc(snd_ctl_card_info_t **ptr) { @@ -1948,8 +2004,10 @@ int snd_ctl_card_info_malloc(snd_ctl_card_info_t **ptr) }
/** - * \brief frees a previously allocated #snd_ctl_card_info_t - * \param obj pointer to object to free + * \brief Free an #snd_ctl_card_info_t previously allocated using + * snd_ctl_card_info_malloc(). + * + * \param obj Pointer to the snd_ctl_card_info_t. */ void snd_ctl_card_info_free(snd_ctl_card_info_t *obj) { @@ -1957,8 +2015,11 @@ void snd_ctl_card_info_free(snd_ctl_card_info_t *obj) }
/** - * \brief clear given #snd_ctl_card_info_t object - * \param obj pointer to object to clear + * \brief Clear given card info object. + * + * See snd_ctl_elem_value_t for details. + * + * \param obj Card info object. */ void snd_ctl_card_info_clear(snd_ctl_card_info_t *obj) { @@ -1966,9 +2027,10 @@ void snd_ctl_card_info_clear(snd_ctl_card_info_t *obj) }
/** - * \brief copy one #snd_ctl_card_info_t to another - * \param dst pointer to destination - * \param src pointer to source + * \brief Bitwise copy of a #snd_ctl_card_info_t object. + * + * \param dst Pointer to destination. + * \param src Pointer to source. */ void snd_ctl_card_info_copy(snd_ctl_card_info_t *dst, const snd_ctl_card_info_t *src) { @@ -1977,9 +2039,12 @@ void snd_ctl_card_info_copy(snd_ctl_card_info_t *dst, const snd_ctl_card_info_t }
/** - * \brief Get card number from a CTL card info - * \param obj CTL card info - * \return card number + * \brief Get the sound card index from the given info object. + * + * See snd_ctl_card_info_t for more details. + * + * \param obj The card info object. + * \return Sound card index. */ int snd_ctl_card_info_get_card(const snd_ctl_card_info_t *obj) { @@ -1988,9 +2053,12 @@ int snd_ctl_card_info_get_card(const snd_ctl_card_info_t *obj) }
/** - * \brief Get card identifier from a CTL card info - * \param obj CTL card info - * \return card identifier + * \brief Get the sound card ID from the given info object. + * + * See snd_ctl_card_info_t for more details. + * + * \param obj The card info object. + * \return Sound card ID. */ const char *snd_ctl_card_info_get_id(const snd_ctl_card_info_t *obj) { @@ -1999,9 +2067,12 @@ const char *snd_ctl_card_info_get_id(const snd_ctl_card_info_t *obj) }
/** - * \brief Get card driver name from a CTL card info - * \param obj CTL card info - * \return card driver name + * \brief Get the sound card driver from the given info object. + * + * See snd_ctl_card_info_t for more details. + * + * \param obj The card info object. + * \return The sound card driver. */ const char *snd_ctl_card_info_get_driver(const snd_ctl_card_info_t *obj) { @@ -2010,9 +2081,12 @@ const char *snd_ctl_card_info_get_driver(const snd_ctl_card_info_t *obj) }
/** - * \brief Get card name from a CTL card info - * \param obj CTL card info - * \return card name + * \brief Get the sound card name from the given info object. + * + * See snd_ctl_card_info_t for more details. + * + * \param obj The card info object. + * \return Sound card name. */ const char *snd_ctl_card_info_get_name(const snd_ctl_card_info_t *obj) { @@ -2021,9 +2095,12 @@ const char *snd_ctl_card_info_get_name(const snd_ctl_card_info_t *obj) }
/** - * \brief Get card long name from a CTL card info - * \param obj CTL card info - * \return card long name + * \brief Get the sound cards long name from the given info object. + * + * See snd_ctl_card_info_t for more details. + * + * \param obj The card info object. + * \return Sound cards long name. */ const char *snd_ctl_card_info_get_longname(const snd_ctl_card_info_t *obj) { @@ -2032,9 +2109,12 @@ const char *snd_ctl_card_info_get_longname(const snd_ctl_card_info_t *obj) }
/** - * \brief Get card mixer name from a CTL card info - * \param obj CTL card info - * \return card mixer name + * \brief Get the sound card mixer name from the given info object. + * + * See snd_ctl_card_info_t for more details. + * + * \param obj The card info object. + * \return Sound card mixer name. */ const char *snd_ctl_card_info_get_mixername(const snd_ctl_card_info_t *obj) { @@ -2043,9 +2123,12 @@ const char *snd_ctl_card_info_get_mixername(const snd_ctl_card_info_t *obj) }
/** - * \brief Get card component list from a CTL card info - * \param obj CTL card info - * \return card mixer identifier + * \brief Get the sound cards "components" property from the given info object. + * + * See snd_ctl_card_info_t for more details. + * + * \param obj The card info object. + * \return Sound cards "components" property. */ const char *snd_ctl_card_info_get_components(const snd_ctl_card_info_t *obj) {