Homebrew CMI 8738 drivers Options

[d0gbert]

Hi everyone!

I'm currently working on WDM drivers for soundcards based on the C-Media 8738/8768 chip. I plan to release the entire source code under a BSD-like license sometime in the future. I'm mainly interested in the S/PDIF connectivity because the DAC of the card sucks.

For testing, you need:
- a CMI 8738-MX/8768 based soundcard with S/PDIF (which are available for around 10-15 USD)
- Windows 2000/XP

Some of the features are:
- bitperfect S/PDIF output for 16bit 44.1/48/88.2/96kHz stereo signals through kernel streaming / dsound / waveout
- bitperfect AC3/DTS passthrough
- multi-channel output (that disables the S/PDIF output port unfortunately)
- recording support
- basic mixer support
- UART support (but disabled for now)

Apparently, the C-Media chip supports only 16 bit contrary to the claims in their specs. I haven't been able to get 24bit output even with the official drivers. But 96kHz output seems to work fine on the newer 8738 chips.

You can help me by posting your chip version and configuration, and testing whether 16bit/96kHz and 24bit/48kHz output through kernel streaming works (foobar2000, winamp have the necessary plugins). I'm specifically looking for people who have means to tell a 16bit S/PDIF stream from a 24bit stream.
When the driver loads, it prints the version of your chip to the kernel debugger. You need a running instance of DebugView (http://www.sysinternals.com/Utilities/DebugView.html) to catch the strings. In other words: open DebugView before updating the drivers.

Note that the drivers aren't signed, so you have to install them manually (Update Driver => Install from a list or specific location => Don't search. I will choose the driver to install => Continue anyway).
A 64-bit build has been successfully tested, and I'll probably release a build sometime soon.

Here are the download links for the latest version:

http://code.google.com/p/cmediadrivers

So long,

dogbert

This post has been edited by d0gbert: Mar 14 2008, 20:30

[cervicek]

I'm here again with the same problem... I think I've tried all possible combinations including setting SPDIF as default device and almost all versions of ac3filters with different settings. Now I think the problem is in x64 Vista or in ac3filter because the sound is normally sent to receiver as stereo (or prologic) when SPDIF is switched OFF in ac3filter, but when I switched on SPDIF in ac3filter it seems that ac3filter immediatelly stopped receving/sending sound signal because channel level meters in ac3filter stopped to show any signal.
I also tried to use my onboard Realtek AC97 with SPDIF and the result was exactly the same so I'm convinced the problem is in Vista or ac3filter because when I tried testing sound to SPDIF in device settings it worked fine for both AC97 and C-Media. So the cards and drivers can play ac3, receiver can receive it but it doesn't work with ac3filter :-(
Does somebody have working SPDIF on x64Vista with AC97 or C-Media ? Which drivers ? Which ac3filter ?

[d0gbert]

It works perfectly fine here with the 32bit version of vista and media player classic which uses its internal filters for AC3 passthrough.
The driver might have failed to install - the x64 version of vista doesn't allow unsigned drivers, and since I'm not able to sign the drivers by myself or cash out ~500 usd to msft, you will need to disable this policy by pressing F8 each time you boot and selecting the relevant item in the menu.

[qristus]

The driver might have failed to install - the x64 version of vista doesn't allow unsigned drivers, and since I'm not able to sign the drivers by myself or cash out ~500 usd to msft, you will need to disable this policy by pressing F8 each time you boot and selecting the relevant item in the menu.

Just curious - can't you sign drivers without paying money to Microsoft? As far as I can see the authenticode tools should be available with the freely downloadable .NET SDKs, all you need is a code signing certificate which is available from various vendors - the cheapest I've seen so far is Comodo's $99 one, which is a good bit less than $500. There might also be better deals out there if you shop around a bit. If several people need 64-bit drivers you might find enough people willing to sponsor something like that.

Some relevant links:
Windows Kernel-mode Driver Signing Requirements
Signing and Checking Code with Authenticode
.NET Framework SDK v1.1
Comodo code-signing certificates

[Dogbert]

qristus, thanks for the info. The authenticode thing is way cheaper than I thought.

I see two problems though:
1. I wanna remain anonymous for the time being, and the signing authorities require a background check. So this is an obvious conflict.
2. The drivers don't exactly do what the microsoft specifies, e.g.
- the SPDIF interface remains turned on even if DRM stuff is being played
- the driver hasn't been thoroughly checked with Driver Verifier et al. which ensure that the driver meets all the specifications. I'm quite certain that it'll pass these checks with minor or no modification though.
As a result, the certificate might be blacklisted by msft in future patches of Vista, which renders the whole thing useless, of course.

Mayble people will find a way to add a self-made certificate authority to the trusted verification roots of the kernel mode in Vista so it'll chow down all the homebrew drivers which are signed with a certificate which roots to the self-created CA.

Imho, the entire thing with the mandatory driver signing just proves to be a scheme to lock out the user from his system in order to enforce that digital rights managed 'premium content' doesn't get ripped. It doesn't add a thing to the overall security of windows, and it doesn't improve the quality of a driver.