RasPi – USB microphone locks up

lockraspberry piusb-audio

On my RasPi board, Debian Linux, the USB microphone occasionally gets locked up such that nothing can use it. The microphone has a LED which is usually flashing, when it's locked, it turns off.

The utility arecord describes it as follows:

card 1: Device [DYNEX USB MIC Device], device 0:USB Audio [USB Audio]
    Subdevices: 1/1
    Subdevice #0: subdevice #0

When the microphone stops working, arecord gives diagnostics like this:

> arecord -D plughw:1,0 > recording.wav
Recording WAVE 'stdin' : Unsigned 8 bit, Rate 8000 Hz, Mono
arecord: set_params:1145: Unable to install hw_params:
ACCESS:  RW_INTERLEAVED
FORMAT:  U8
etc...

Unplugging and plugging the microphone fixes it, only because the current dip forces the RasPi to reboot! Not an ideal situation.

Is there a way to fix this from the command line or a C executable?

I also tried using ioctl(fd, USBDEVFS_RESET, 0) using the output from lsusb to provide the bus and device number. That turns the LED back on, but it's overkill. The device has to be re-setup using alsamixer.

Best Answer

This is easy to solve.

Issue: Your microphone is not getting enough power. The Raspberry Pi USB ports have issues supplying enough amps to USB devices that need more than power than USB memory cards.

Solution: Get an active USB hub (powered hub plugged into a power source like an outlet.) The hub will power the microphone.

Related Solutions

What is the difference between spin locks and semaphores

Both manage a limited resource. I'll first describe difference between binary semaphore (mutex) and spin lock.

Spin locks perform a busy wait - i.e. it keeps running loop:

while (try_acquire_resource ());
...
release();

It performs very lightweight locking/unlocking but if the locking thread will be preempted by other which will try to access the same resouce the second one will simply try to acquitre resource untill it run out of it CPU quanta.

On the other hand mutex behave more like:

if (!try_lock()) {
    add_to_waiting_queue ();
    wait();
}
...
process *p = get_next_process_from_waiting_queue ();
p->wakeUp ();

Hence if the thread will try to acquire blocked resource it will be suspended till it will be avaible for it. Locking/unlocking is much more heavy but the waiting is 'free' and 'fair'.

Semaphore is a lock that is allowed to be used multiple (known from initialization) number of times - for example 3 threads are allowed to simultainusly hold the resource but no more. It is used for example in producer/consumer problem or in general in queues:

P(resources_sem)
resource = resources.pop()
...
resources.push(resources)
V(resources_sem)

Monitoring file locks, locked using flock

From man lsof:

FD is the File Descriptor number of the file or: FD is followed by one of these characters, describing the mode under which the file is open:

          The mode character is followed by one of these lock characters, describing the type of lock applied to the file:

               R for a read lock on the entire file;
               W for a write lock on the entire file;
               space if there is no lock.

So R in 3uR mean that read/shared lock is issued by 613 PID.

#lsof /tmp/file
COMMAND PID    USER   FD   TYPE DEVICE SIZE/OFF    NODE NAME
perl    613 turkish    3uR  REG    8,2        0 1306357 /tmp/file

Reading directly from /proc/locks is faster than lsof,

perl -F'[:\s]+' -wlanE'
  BEGIN { $inode = (stat(pop))[1]; @ARGV = "/proc/locks" }
  say "pid:$F[4] [$_]" if $F[7] == $inode
' /tmp/file

Best Answer

Related Solutions

What is the difference between spin locks and semaphores

Monitoring file locks, locked using flock

Related Question