3.3.2.3.3 Obtaining Audio v1.0 Device Audio Stream Details
The application will need to know more details about an attached audio device like Number of Audio Stream Groups and audio format details of each audio stream in audio stream group. Application will need to search through all of the audio streams and find if a suitable audio stream is available before it can open a stream and start communicating.
USB_HOST_AUDIO_V1_0_NumberOfStreamGroupsGet function can be used to know how many stream groups are available in the attached Audio device. This function takes USB_HOST_AUDIO_V1_0_OBJ as an argument and returns uint8_t value as number of stream groups.
USB_HOST_AUDIO_V1_0_StreamGetFirst function can be used to find out audio format details of first audio stream in a Stream Groups. This function takes USB_HOST_AUDIO_V1_0_OBJ, stream group index and pointer to the USB_HOST_AUDIO_V1_0_STREAM_INFO as arguments. The stream index can any number between zero to number of stream groups returned by USB_HOST_AUDIO_V1_0_NumberOfStreamGroupsGet function. The audio stream object returned as part of USB_HOST_AUDIO_V1_0_STREAM_OBJ structure.
USB_HOST_AUDIO_V1_0_StreamGetNext function can be used to find details about subsequent audio streams. When there are no more audio streams available in the specified audio stream group this function return USB_HOST_AUDIO_V1_0_RESULT_END_OF_STREAM_LIST error. It is application’s responsibility to map and Audio Stream group and an audio stream.
If the application is looking for a audio stream with certain properties, application need compare audio stream properties with members of the USB_HOST_AUDIO_V1_0_STREAM_INFO structure returned by USB_HOST_AUDIO_V1_0_StreamGetFirst and USB_HOST_AUDIO_V1_0_StreamGetNext functions.
/* This code shows an example of getting details about audio stream
in an attached Audio v1.0 device.*/
/* Specify the Audio Stream format details that this application supports */
const APP_USB_HOST_AUDIO_STREAM_FORTMAT audioSpeakerStreamFormat =
{
.streamDirection = USB_HOST_AUDIO_V1_0_DIRECTION_OUT,
.format = USB_AUDIO_FORMAT_PCM,
.nChannels = 2,
.bitResolution = 16,
.subFrameSize = 2,
.samplingRate = 48000
};
bool isAudioDeviceAttached = false;
USB_HOST_AUDIO_V1_0_OBJ audioDeviceObj;
/*************************************************************/
/* Function to search for a specific Audio Stream */
/************************************************************/
USB_HOST_AUDIO_V1_0_STREAM_OBJ App_USBHostAudioSpeakerStreamFind
(
USB_HOST_AUDIO_V1_0_OBJ audioDeviceObj,
APP_USB_HOST_AUDIO_STREAM_FORTMAT audioStream,
uint8_t* numberofStreamGroups
)
{
USB_HOST_AUDIO_V1_0_RESULT result;
USB_HOST_AUDIO_V1_0_STREAM_INFO streamInfo;
/* Get Number of Stream Groups */
*numberofStreamGroups = USB_HOST_AUDIO_V1_0_NumberOfStreamGroupsGet(audioDeviceObj);
if (*numberofStreamGroups == 0)
{
return (USB_HOST_AUDIO_V1_0_STREAM_OBJ)0;
}
/* Get the First Stream Information in the Stream Group */
result = USB_HOST_AUDIO_V1_0_StreamGetFirst(appData.audioDeviceObj, 0, &streamInfo);
if (result == USB_HOST_AUDIO_V1_0_RESULT_SUCCESS)
{
/* Compare Audio Stream info */
if ((streamInfo.format == audioStream.format)
&& (streamInfo.streamDirection == audioStream.streamDirection)
&& (streamInfo.nChannels == audioStream.nChannels)
&& (streamInfo.bitResolution == audioStream.bitResolution)
&& (streamInfo.subFrameSize == audioStream.subFrameSize))
{
return streamInfo.streamObj;
}
}
return (USB_HOST_AUDIO_V1_0_STREAM_OBJ)0;
}
/*************************************************************/
/* Audio attach event listener function */
/************************************************************/
void APP_USBHostAudioAttachEventListener
(
USB_HOST_AUDIO_V1_0_OBJ audioObj,
USB_HOST_AUDIO_V1_0_EVENT event,
uintptr_t context
)
{
/* This function gets called when the Audio v1.0 device is attached/detached. In this
* example we let the application know that a device is attached and we
* store the Audio v1.0 device object. This object will be required to open the
* device. */
switch (event)
{
case USB_HOST_AUDIO_V1_0_EVENT_ATTACH:
if (isAudioDeviceAttached == false)
{
isAudioDeviceAttached = true;
audioDeviceObj = audioObj;
}
else
{
/* This application supports only one Audio Device . Handle Error Here.*/
}
break;
case USB_HOST_AUDIO_V1_0_EVENT_DETACH:
if (isAudioDeviceAttached == true)
{
/* This means the device was detached. There is no event data
* associated with this event.*/
isAudioDeviceAttached = false;
break;
}
break;
}
}
/*************************************************************/
/* Audio Tasks function */
/************************************************************/
void APP_Tasks ( void )
{
USB_HOST_AUDIO_V1_0_RESULT audioResult;
USB_HOST_AUDIO_V1_0_STREAM_RESULT streamResult;
/* Check the application's current state. */
switch ( appData.state )
{
case APP_STATE_BUS_ENABLE:
/* Register a callback for Audio Device Attach. */
audioResult = USB_HOST_AUDIO_V1_0_AttachEventHandlerSet
(
&APP_USBHostAudioAttachEventListener,
(uintptr_t)0
);
if (audioResult == USB_HOST_AUDIO_V1_0_RESULT_SUCCESS )
{
/* Set Host Event Handler */
USB_HOST_EventHandlerSet(APP_USBHostEventHandler, 0);
USB_HOST_BusEnable(0);
/* Advance application state */
appData.state = APP_STATE_WAIT_FOR_BUS_ENABLE_COMPLETE;
}
break;
case APP_STATE_WAIT_FOR_BUS_ENABLE_COMPLETE:
if(USB_HOST_BusIsEnabled(0))
{
appData.state = APP_STATE_WAIT_FOR_DEVICE_ATTACH;
}
break;
case APP_STATE_WAIT_FOR_DEVICE_ATTACH:
/* Check if an Audio Device has been attached */
if(appData.isAudioDeviceAttached == true)
{
appData.nAudioStreamGroups = 0;
/* Find an Audio Stream matching to our requirement */
appData.ouStreamObj = App_USBHostAudioSpeakerStreamFind
(
appData.audioDeviceObj,
audioSpeakerStreamFormat,
&appData.nAudioStreamGroups
);
if (appData.nAudioStreamGroups == 0)
{
appData.state = APP_STATE_ERROR;
break;
}
}
break;
default:
break;
}
}