nuttx/audio: improve null audio driver.

This patch aims to enhance the null audio driver through reading and writing files.
With it, you can conveniently customize and define various capture or playback audio drivers
for debugging or automated testing.

Change-Id: If39eb9db4bbfdf31ab313346b42242b8a125388c
Signed-off-by: yaojingwei <yaojingwei@xiaomi.com>

arch/sim/src/sim/sim_initialize.c

@@ -26,6 +26,7 @@
 
 #include <nuttx/arch.h>
 #include <nuttx/audio/audio.h>
+#include <nuttx/audio/audio_null.h>
 #include <nuttx/kthread.h>
 #include <nuttx/motor/foc/foc_dummy.h>
 #include <nuttx/mtd/mtd.h>
@@ -298,6 +299,12 @@ void up_initialize(void)
 
   audio_register("mixer", sim_audio_initialize(false, false));
 
+#if defined(CONFIG_AUDIO_NULL) && defined(CONFIG_AUDIO_NULL_DEVICE_PARAMS)
+  /* Register null audio driver */
+
+  null_audio_register();
+#endif
+
 #endif
 
 #ifdef CONFIG_SIM_USB_DEV

cmake/nuttx_mkconfig.cmake

@@ -69,6 +69,7 @@ set(DEQUOTELIST
     "CONFIG_TTY_LAUNCH_ENTRYPOINT" # Name of entry point from tty launch
     "CONFIG_TTY_LAUNCH_ARGS" # Argument list of entry point from tty launch
     "CONFIG_BOARD_MEMORY_RANGE" # Memory range for board
+    "CONFIG_AUDIO_NULL_DEVICE_PARAMS" # Arguments for the null audio device
     # NxWidgets/NxWM
     "CONFIG_NXWM_BACKGROUND_IMAGE" # Name of bitmap image class
     "CONFIG_NXWM_CALIBRATION_ICON" # Name of bitmap image class

drivers/audio/Kconfig

@@ -505,6 +505,33 @@ config AUDIO_NULL_WORKER_STACKSIZE
 	int "Null audio device worker thread stack size"
 	default 768
 
+config AUDIO_NULL_DEVICE_PARAMS
+	string "Null audio device params"
+	default ""
+	---help---
+		This is a params for null audio device. The params is following format:
+		{dev_name, mode, sample_rates[4], channels, format[4], period_time, periods}.
+
+		- dev_name (string): pcm2c or pcm2p or others.
+		- mode     (string): playback or capture.
+		- sample_rates(uint32 array): {16000, 32000}.
+		- channels  (uint8, {min_chan, max_chan}): {1, 2}.
+		- format(uint8 array): {8,16,32}.
+		- period_time(uint32): 100, unit ms.
+		- periods    (uint32): 4, buffer cnt.
+		e.g:
+			{"pcm2c", "capture", {8000, 16000, 44100}, {1, 2}, {16}, 100, 4},
+			{"pcm2p", "playback", {8000, 16000, 44100}, {1, 2}, {16}, 100, 4},
+
+config AUDIO_NULL_DATA_PATH
+	string "Null audio device data path"
+	default "/data/"
+	---help---
+		This dir is used to store the audio file for virtual capture or playback device.
+		The filename for capture device should comply with the format "devname_samplerate_channels_format.pcm".
+		e.g: pcm2c_16000_2_16.pcm.
+		The filename format of playback device is the same as capture device.
+		e.g: pcm2p_16000_2_16.pcm.
 endif # AUDIO_NULL
 
 config AUDIO_I2S