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authorRuslan Bilovol2017-06-18 16:23:54 +0300
committerFelipe Balbi2017-06-19 09:22:47 +0300
commit0591bc2360152f851e29246884805bb77a2c3b9d (patch)
treeb0b46346b588758f86db17e04f47a4b832cfd2f7 /Documentation/usb
parentd355339eecd986648420e05f8c958fbc78dbb382 (diff)
usb: gadget: add f_uac1 variant based on a new u_audio api
This patch adds a new function 'f_uac1' (f_uac1 with virtual "ALSA card") that uses recently created u_audio API. Comparing to legacy f_uac1 function implementation it doesn't require any real Audio codec to be present on the device. In f_uac1 audio streams are simply sinked to and sourced from a virtual ALSA sound card created using u_audio API. Legacy f_uac1 approach is to write audio samples directly to existing ALSA sound card f_uac1 approach is more generic/flexible one - create an ALSA sound card that represents USB Audio function and allows to be used by userspace application that may choose to do whatever it wants with the data received from the USB Host and choose to provide whatever it wants as audio data to the USB Host. f_uac1 also has capture support (gadget->host) thanks to easy implementation via u_audio. By default, capture interface has 48000kHz/2ch configuration, same as playback channel has. f_uac1 descriptors naming convention uses f_uac2 driver naming convention that makes it more common and meaningful. Comparing to f_uac1_legacy, the f_uac1 doesn't have volume/mute functionality. This is because the f_uac1 volume/mute feature unit was dummy implementation since that driver creation (2009) and never had any real volume control or mute functionality, so there is no any difference here. Since f_uac1 functionality, exposed interface to userspace (virtual ALSA card), input parameters are so different comparing to f_uac1_legacy, that there is no any reason to keep them in the same file/module, and separate function was created. g_audio can be built using one of existing UAC functions (f_uac1, f_uac1_legacy or f_uac2) Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Diffstat (limited to 'Documentation/usb')
-rw-r--r--Documentation/usb/gadget-testing.txt44
1 files changed, 44 insertions, 0 deletions
diff --git a/Documentation/usb/gadget-testing.txt b/Documentation/usb/gadget-testing.txt
index ce51d6e4e7d0..fbc397d17e98 100644
--- a/Documentation/usb/gadget-testing.txt
+++ b/Documentation/usb/gadget-testing.txt
@@ -20,6 +20,7 @@ provided by gadgets.
17. UAC2 function
18. UVC function
19. PRINTER function
+20. UAC1 function (new API)
1. ACM function
@@ -773,3 +774,46 @@ host:
More advanced testing can be done with the prn_example
described in Documentation/usb/gadget-printer.txt.
+
+
+20. UAC1 function (virtual ALSA card, using u_audio API)
+=================
+
+The function is provided by usb_f_uac1.ko module.
+It will create a virtual ALSA card and the audio streams are simply
+sinked to and sourced from it.
+
+Function-specific configfs interface
+------------------------------------
+
+The function name to use when creating the function directory is "uac1".
+The uac1 function provides these attributes in its function directory:
+
+ c_chmask - capture channel mask
+ c_srate - capture sampling rate
+ c_ssize - capture sample size (bytes)
+ p_chmask - playback channel mask
+ p_srate - playback sampling rate
+ p_ssize - playback sample size (bytes)
+ req_number - the number of pre-allocated request for both capture
+ and playback
+
+The attributes have sane default values.
+
+Testing the UAC1 function
+-------------------------
+
+device: run the gadget
+host: aplay -l # should list our USB Audio Gadget
+
+This function does not require real hardware support, it just
+sends a stream of audio data to/from the host. In order to
+actually hear something at the device side, a command similar
+to this must be used at the device side:
+
+$ arecord -f dat -t wav -D hw:2,0 | aplay -D hw:0,0 &
+
+e.g.:
+
+$ arecord -f dat -t wav -D hw:CARD=UAC1Gadget,DEV=0 | \
+aplay -D default:CARD=OdroidU3