1 Proc Files of ALSA Drivers 2 ========================== 3 Takashi Iwai <tiwai@suse.de> 4 5General 6------- 7 8ALSA has its own proc tree, /proc/asound. Many useful information are 9found in this tree. When you encounter a problem and need debugging, 10check the files listed in the following sections. 11 12Each card has its subtree cardX, where X is from 0 to 7. The 13card-specific files are stored in the card* subdirectories. 14 15 16Global Information 17------------------ 18 19cards 20 Shows the list of currently configured ALSA drivers, 21 index, the id string, short and long descriptions. 22 23version 24 Shows the version string and compile date. 25 26modules 27 Lists the module of each card 28 29devices 30 Lists the ALSA native device mappings. 31 32meminfo 33 Shows the status of allocated pages via ALSA drivers. 34 Appears only when CONFIG_SND_DEBUG=y. 35 36hwdep 37 Lists the currently available hwdep devices in format of 38 <card>-<device>: <name> 39 40pcm 41 Lists the currently available PCM devices in format of 42 <card>-<device>: <id>: <name> : <sub-streams> 43 44timer 45 Lists the currently available timer devices 46 47 48oss/devices 49 Lists the OSS device mappings. 50 51oss/sndstat 52 Provides the output compatible with /dev/sndstat. 53 You can symlink this to /dev/sndstat. 54 55 56Card Specific Files 57------------------- 58 59The card-specific files are found in /proc/asound/card* directories. 60Some drivers (e.g. cmipci) have their own proc entries for the 61register dump, etc (e.g. /proc/asound/card*/cmipci shows the register 62dump). These files would be really helpful for debugging. 63 64When PCM devices are available on this card, you can see directories 65like pcm0p or pcm1c. They hold the PCM information for each PCM 66stream. The number after 'pcm' is the PCM device number from 0, and 67the last 'p' or 'c' means playback or capture direction. The files in 68this subtree is described later. 69 70The status of MIDI I/O is found in midi* files. It shows the device 71name and the received/transmitted bytes through the MIDI device. 72 73When the card is equipped with AC97 codecs, there are codec97#* 74subdirectories (described later). 75 76When the OSS mixer emulation is enabled (and the module is loaded), 77oss_mixer file appears here, too. This shows the current mapping of 78OSS mixer elements to the ALSA control elements. You can change the 79mapping by writing to this device. Read OSS-Emulation.txt for 80details. 81 82 83PCM Proc Files 84-------------- 85 86card*/pcm*/info 87 The general information of this PCM device: card #, device #, 88 substreams, etc. 89 90card*/pcm*/xrun_debug 91 This file appears when CONFIG_SND_DEBUG=y and 92 CONFIG_PCM_XRUN_DEBUG=y. 93 This shows the status of xrun (= buffer overrun/xrun) and 94 invalid PCM position debug/check of ALSA PCM middle layer. 95 It takes an integer value, can be changed by writing to this 96 file, such as 97 98 # echo 5 > /proc/asound/card0/pcm0p/xrun_debug 99 100 The value consists of the following bit flags: 101 bit 0 = Enable XRUN/jiffies debug messages 102 bit 1 = Show stack trace at XRUN / jiffies check 103 bit 2 = Enable additional jiffies check 104 bit 3 = Log hwptr update at each period interrupt 105 bit 4 = Log hwptr update at each snd_pcm_update_hw_ptr() 106 bit 5 = Show last 10 positions on error 107 bit 6 = Do above only once 108 109 When the bit 0 is set, the driver will show the messages to 110 kernel log when an xrun is detected. The debug message is 111 shown also when the invalid H/W pointer is detected at the 112 update of periods (usually called from the interrupt 113 handler). 114 115 When the bit 1 is set, the driver will show the stack trace 116 additionally. This may help the debugging. 117 118 Since 2.6.30, this option can enable the hwptr check using 119 jiffies. This detects spontaneous invalid pointer callback 120 values, but can be lead to too much corrections for a (mostly 121 buggy) hardware that doesn't give smooth pointer updates. 122 This feature is enabled via the bit 2. 123 124 Bits 3 and 4 are for logging the hwptr records. Note that 125 these will give flood of kernel messages. 126 127 When bit 5 is set, the driver logs the last 10 xrun errors and 128 the proc file shows each jiffies, position, period_size, 129 buffer_size, old_hw_ptr, and hw_ptr_base values. 130 131 When bit 6 is set, the full xrun log is shown only once. 132 133card*/pcm*/sub*/info 134 The general information of this PCM sub-stream. 135 136card*/pcm*/sub*/status 137 The current status of this PCM sub-stream, elapsed time, 138 H/W position, etc. 139 140card*/pcm*/sub*/hw_params 141 The hardware parameters set for this sub-stream. 142 143card*/pcm*/sub*/sw_params 144 The soft parameters set for this sub-stream. 145 146card*/pcm*/sub*/prealloc 147 The buffer pre-allocation information. 148 149 150AC97 Codec Information 151---------------------- 152 153card*/codec97#*/ac97#?-? 154 Shows the general information of this AC97 codec chip, such as 155 name, capabilities, set up. 156 157card*/codec97#0/ac97#?-?+regs 158 Shows the AC97 register dump. Useful for debugging. 159 160 When CONFIG_SND_DEBUG is enabled, you can write to this file for 161 changing an AC97 register directly. Pass two hex numbers. 162 For example, 163 164 # echo 02 9f1f > /proc/asound/card0/codec97#0/ac97#0-0+regs 165 166 167USB Audio Streams 168----------------- 169 170card*/stream* 171 Shows the assignment and the current status of each audio stream 172 of the given card. This information is very useful for debugging. 173 174 175HD-Audio Codecs 176--------------- 177 178card*/codec#* 179 Shows the general codec information and the attribute of each 180 widget node. 181 182card*/eld#* 183 Available for HDMI or DisplayPort interfaces. 184 Shows ELD(EDID Like Data) info retrieved from the attached HDMI sink, 185 and describes its audio capabilities and configurations. 186 187 Some ELD fields may be modified by doing `echo name hex_value > eld#*`. 188 Only do this if you are sure the HDMI sink provided value is wrong. 189 And if that makes your HDMI audio work, please report to us so that we 190 can fix it in future kernel releases. 191 192 193Sequencer Information 194--------------------- 195 196seq/drivers 197 Lists the currently available ALSA sequencer drivers. 198 199seq/clients 200 Shows the list of currently available sequencer clients and 201 ports. The connection status and the running status are shown 202 in this file, too. 203 204seq/queues 205 Lists the currently allocated/running sequencer queues. 206 207seq/timer 208 Lists the currently allocated/running sequencer timers. 209 210seq/oss 211 Lists the OSS-compatible sequencer stuffs. 212 213 214Help For Debugging? 215------------------- 216 217When the problem is related with PCM, first try to turn on xrun_debug 218mode. This will give you the kernel messages when and where xrun 219happened. 220 221If it's really a bug, report it with the following information: 222 223 - the name of the driver/card, show in /proc/asound/cards 224 - the register dump, if available (e.g. card*/cmipci) 225 226when it's a PCM problem, 227 228 - set-up of PCM, shown in hw_parms, sw_params, and status in the PCM 229 sub-stream directory 230 231when it's a mixer problem, 232 233 - AC97 proc files, codec97#*/* files 234 235for USB audio/midi, 236 237 - output of lsusb -v 238 - stream* files in card directory 239 240 241The ALSA bug-tracking system is found at: 242 243 https://bugtrack.alsa-project.org/alsa-bug/ 244