audioens in VMware...

So, we have not had audio in OpenSolaris within VMware since... well, ever.

I've been doing some investigation. I'm seeing a situation where the VMware emulated audioens device behaves rather differently from the real hardware.

For one, it seems to insist on using real interrupts. In particular, the sample count registers do not appear to be updated unless one receives and acknowledges an interrupt. (By toggling the interrupt enable bit.) This means that this virtualized device will never be able to run "interrupt free" like the other audio devices (or real audio hardware).

For another, it appears that the audio device has some weird dependency on the relationship between the size of the audio buffer, and the interrupt rate (the number of samples at which to interrupt). Using different values gives, strange results.

Finally, I cannot, for the life of me, figure out how to cause the device to actually trigger an interrupt. I've been able to make some progress by simulating a soft interrupt at 100Hz, which is how the interrupt free framework works anyway, but from what I can tell, nothing is causing a real interrupt to be delivered. This is really strange. (Without this functionality, I am able to process audio at a reasonable rate, but it still stutters, and is not really suitable for real-world use.)

My guess is that the virtual device has some weird dependencies that we don't know about. For example, while the hardware spec identifies registers as being 8, 16, or 32 bits wide, and we use those at the right bit widths, other FOSS drivers all seem to just blithely use 32-bit wide accesses. Is there a hidden dependency here?

If any reader from VMware is seeing this, and can help me understand the behavior of the simulated device, I'd appreciate it. I'd like to make audio work in this environment, if possible. I'm pretty close, I think.

Actually, it seems kind of crazy that these environments emulate such complex audio hardware. (For example sophisticated sample rate conversion hardware.) Much better, I think, would be a simple paravirtualization driver that just exposes a simple buffer and some control functions. If someone at VMware wants to work on that as a solution, I'd be happy to help with Solaris support for it. Since these things run isochronously, and chew up a fair bit of cpu when they run, such a solution would probably be quite useful. (For example, its silly to perform multiple sample rate conversions in software... instead we could express native sample rates via a PV driver to the guest, ensuring only a single SRC operation is performed appropriately in the guest operating system.)


Comments

Post a Comment

Popular posts from this blog

An important milestone

Yesterday, with very little fanfare, illumos passed an important milestone. This milestone was the integration of  195 Need replacement for nfs/lockd+klm This is work that I originally tasked Gordon Ross and Dan Kruchinin to work while we were colleagues at  Nexenta .  Gordon started the work, picking up bits from FreeBSD as a starting point and gluing it to the illumos entry points.  Dan continued with it, and fleshed out a lot of the skeleton that Gordon had started.  It was subsequently picked up by the engineers at Delphix , and -- after some important bug fixing work was completed -- was integrated into their product quite some time ago -- reportedly its been stable since December in their product. The reason this is such an important milestone, is two fold: First, this represents a substantial collaborative effort, involving contributions from parties across several organizational boundaries.  The level of collaboration achieved here is a w...
Read more

GNU grep - A Cautionary Tale About GPLv3

My company, DEY Storage Systems , is in the process of creating a new product around the illumos operating system.  As you might imagine, this product includes a variety of open and proprietary source code.  The product itself is not delivered as a separate executable, but as a complete product.  We don't permit our customers to crack it open, both from the sense of protecting our IP, but also to protect our support and release engineering organizations -- our software releases consist only of a single file and we don't supply tools or source for other parties to modify that file. One of the pieces that we wanted to integrate into the tree is an excellent little piece of software called Zookeeper , produced by the Apache organization.  Like illumos, Zookeeper has a nice non-viral copyleft license, which makes it nice for integration into our product. However, I discovered that as part of our integration, one of my engineers had decided to integrate GNU grep. ...
Read more

The Hand May Be Forced

Well, as you may have read , Oracle has decided that at some point very soon, we're going to lose normal regular access to the source code for OS/Net. (I.e. the Solaris kernel and supporting programs.) While I would have vastly preferred for Illumos to have a cooperative and collaborative relationship with Oracle , it appears that Oracle doesn't value this. In fact, the exact words were from the management at Oracle were as follows: Solaris is not something we outsource to others, it is not the assembly of someone else’s technology, and it is not a sustaining-only product. While I understand the need to own the technology, there are few things that could be stated that show a stronger NIH attitude than this. Its unlikely that there will ever be a way for Oracle and the greater community to have a collaborative relationship. This is a dark day for OpenSolaris -- its effectively dead now. (Its parent, Solaris, lives on however.) How unfortunate. For Oracle that is. Because...
Read more