MX233 192kHz Audio Using an External USB DAC

[jackyliu]

1) Played a 192/24 pcm sample from the NAND. No improvement. The result was the same as playing from a usb storage.
2) Measured Freescale's USB bandwidth by copying a file from one usb storage to another (with USB hub). The speed was about 50 Mbits/second which should definitely be enough or 192/24 content playback - it needs approx 20 Mbits (192kHz * 24 Bits * 2 channels * 2 paths - one for reading data from USB storage and other for sending them to USB DAC).

[jackyliu]

This is my suggestion:

1.Run CPU at full speed for testing. You can use below command to check CPU frequecny:
cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
i.mx233 can work at the high frequency at 454736.
2. The required bandwidth is ( 192000 * 4 bytes * 2 channels ) = 1.5 MB/s. Dividing to 1000 frames in USB transaction we get 1536 bytes per frame. We need at least 3 frames filled with data (better 10-15) to operate properly. This is about 5-20 KB of outgoing buffers to be allocated in USB engine and in ALSA circular buffer system.
a.Please try to increase ALSA buffer count and buffer size very significantly (10x, for example). This could be done via ALSA API (snd_pcm_hw_params) or via APLAY command line params (http://linux.die.net/man/1/aplay).
b.Please check if there is enough space allocated in USB drivers. You can check ehci-mem.c, ehci-q.c.
c.Please disable SPDIF transmitter.