| | Open Sound System |
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oss_mixerinfo mi;
mi.dev = The mixer device number.
ioctl(fd, SNDCTL_MIXERINFO, &mi);
The above code fragment lacks all error checks for clarity. Real world applications must always check for the errors and handle them as described below. Also most OSS ioctl calls will return information in the argument variable and it's usually necessary to check it too.
This ioctl call is supported by all OSS devices, including audio, mixer and MIDI devices. The device for which the information is returned is selected by the dev field of the argument. If dev is set to -1 then information for the current mixer device pointed by the file descriptor (fd) will be returned.
Some OSS implementations may reject the call if dev is not set to -1. For this reason it's recommended that applications open the right device directly and use -1 as the device number.
The oss_mixerinfo structure contains the following fields.
| Field | Description |
dev | The mixer device number. Must be set prior the call (see above). |
id | A short mnemonic identifier of the device. |
name | A string that contains the "full" descriptive name of the device. |
modify_counter | This integer field will be incremented every time any control under this mixer device gets changed. Applications can poll this field and perform a screen update if the value changes. However note that this field will not be incremented when controls like peak meters change their value. Controls that need to be polled regardless of the modify_counter will be marked with the MIXF_POLL flag. |
card_number | Number of the sound card where this device belongs or -1 if this information is not available. Applications should normally not use this field for any purpose. |
port_number | Usually 0. May be higher if the same card has multiple mixers. This field should not be used by applications. |
magic | Reserved for internal use by the utilities included in OSS. |
enabled | Usually 1 which means that the device is available for use. Value of 0 means that the device may have been unplugged or the driver is currently not loaded in the system. Unavailable devices cannot necessarily be opened for the time being. However they are part of the device configuration and they may become available again after few moments. |
caps | Mixer device capabilities (see below). |
flags | Reserved for internal use by OSS. Must not be used by any applications. |
nrext | Number of new style mixer (extension) info records available for this mixer. Use SNDCTL_MIX_EXTINFO to obtain the actual extension info records. SNDCTL_MIX_NREXT ioctl is an alternative way to get the number of mixer extensions. |
priority | This priority field can be used to select the "default" mixer device which is usually connected to the motherboard sound chip. The mixer device with the highest priority is the preferred mixer. If two or more devices ahare the same number then the first one should be used. Value of -2 or below means that the device must not be used as a default mixer even if it's the only mixer device in the system. |
devnode | This field contains the name of the device file associated with this mixer device. For example "/dev/oss/sblive0/mix0". Mixer applications usually use "/dev/mixer" so this field has very limited use. |
legacy_device | This field gives the old style /dev/mixer# device number related with this mixer device. This information is not necessarily up to date in all situations. Mixer applications usually use "/dev/mixer" so this field has very limited use. |
| Source | Explanation |
| MIXER_CAP_LAYOUT_B | The device needs nonstandard layout policy |
| MIXER_CAP_NARROW | The GUI for this device should be made as narrow as possible |
| MIXER_CAP_VIRTUAL | The device is virtual (doesn't control hardware directly) |
You can use the SNDCTL_SYSINFO ioctl to find out how many mixer devices there are in the system.
The return value from the OSS ioctl calls will be -1 if a fatal error occurred. Other values mean that the ioctl call was more or less successful. However in most cases the application must check the value returned in the argument to see what was the accepted value.
Please see the Possible error codes (errno) returned by OSS calls section for more info about the error codes returned by OSS.
| ossinfo.c | The ossinfo program that is included in the OSS package. |
| ossxmix.c | This is the ossxmix (GTK++ GUI) program shipped with OSS |
| ossmix.c | Sources for the ossmix command line mixer shipped with OSS |
| mixer_applet.c | A sample program for developing a simple mixer applet. |