i.MX Processors中的主题 MX233 192kHz Audio Using an External USB DAC https://community.nxp.com/t5/i-MX-Processors/MX233-192kHz-Audio-Using-an-External-USB-DAC/m-p/202654#M11329 <HTML><HEAD></HEAD><BODY><P>1) Played a 192/24 pcm sample from the NAND. No improvement. The result was the same as playing from a usb storage.<BR />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).</P></BODY></HTML> Mon, 16 Jan 2012 08:33:46 GMT jackyliu 2012-01-16T08:33:46Z MX233 192kHz Audio Using an External USB DAC https://community.nxp.com/t5/i-MX-Processors/MX233-192kHz-Audio-Using-an-External-USB-DAC/m-p/202654#M11329 <HTML><HEAD></HEAD><BODY><P>1) Played a 192/24 pcm sample from the NAND. No improvement. The result was the same as playing from a usb storage.<BR />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).</P></BODY></HTML> Mon, 16 Jan 2012 08:33:46 GMT https://community.nxp.com/t5/i-MX-Processors/MX233-192kHz-Audio-Using-an-External-USB-DAC/m-p/202654#M11329 jackyliu 2012-01-16T08:33:46Z Re: MX233 192kHz Audio Using an External USB DAC https://community.nxp.com/t5/i-MX-Processors/MX233-192kHz-Audio-Using-an-External-USB-DAC/m-p/202655#M11330 <HTML><HEAD></HEAD><BODY><P>This is my suggestion:</P><P>1.Run CPU at full speed for testing. You can use below command to check CPU frequecny:<BR />cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq<BR />i.mx233 can work at the high frequency at 454736.<BR />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.<BR />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 (<A href="http://linux.die.net/man/1/aplay" target="_blank">http://linux.die.net/man/1/aplay</A>).<BR />b.Please check if there is enough space allocated in USB drivers. You can check ehci-mem.c, ehci-q.c.<BR />c.Please disable SPDIF transmitter.</P></BODY></HTML> Mon, 16 Jan 2012 08:35:14 GMT https://community.nxp.com/t5/i-MX-Processors/MX233-192kHz-Audio-Using-an-External-USB-DAC/m-p/202655#M11330 jackyliu 2012-01-16T08:35:14Z