Dear List,
Hello. I'm new here. This is my first attempt to hack an alsa driver.
I recently purchased a "Sound Blaster Audigy Value!" card for use in a MythTV box. As I have a digital receiver, I was mainly concerned with getting a working S/PDIF output (coax or optical) and not too much more.
Summary: I can make 44.1kHz digital output work, but I think that the driver model of the card having 3 or 4 digital output channels is incorrect. I believe the card only has 1 digital output channel.
Details:
The card I have is characterised by the following: http://www.soundblaster.com/products/product.asp?category=1&subcategory=... Model: SB0570 serial: 100a1102 Also known as: Sound Blaster Audigy SE
During initial testing, I noticed that 44.1kHz playback was not implemented. Subsequent testing shows that speaker-test works fine with 48kHz, 96kHz and 192kHz. (I only tested 16bit output so far.)
I noticed in the source code that 44.1k was explicitly disabled. I added code in snd_ca0106_pcm_prepare_playback to set up this rate for S/PDIF output as per the comments in ca0106.h . Initial tests using hw:0,0 at 44.1kHz produced recognisable signals with some noisy corruption. Later I accidentally discovered that serially opening hw:0,2 , hw:0,1 and hw:0,0 at 44.1kHz then produces perfectly good 44.1kHz sampled digital audio output. Removing hw:0,1 or hw:0,2 from this sequence causes noisy corruption. It seems that channels 0-2 in reg40 must all be set to the same sampling frequency for S/PDIF to work where 44.1kHz is concerned. Conversely, to sucessfully output 48kHz again, I have to open hw:0,2 , hw:0,1 and hw:0,0 at 48kHz to restore proper output. I do not have such troubles with 96kHz and 192kHz, for which it suffices to just open hw:0,0 at the relevant sampling rate.
Using these tricks, I can successfully output 44.1kHz encoded Dolby Digital and DTS signals (found at http://www.sr.se/cgi-bin/mall/index.asp?programid=2445 , as mentioned at http://alsa.opensrc.org/DigitalOut . )
Later, I examined the product manual (from a Windows compressed helpfile on the CD), and noticed that Creative instruct you to connect to the blue socket in only two ways: 1) with a mono 3.5mm jack plug to RCA plug -> S/PDIF input to external device, and 2) a proprietary digital I/O module (see http://www.soundblaster.com/products/product.asp?category=1&subcategory=... ) The digital I/O module only has one input and one output (the optical/coaxial pairs are duplicates of each other).
The manual does not say how to connect a S/PDIF input signal other than through the digital I/O module.
This suggests to me that the following comment near the top of ca0106_main.c is incorrect for the SB0570:
* ( In theory one could output 3 different AC3 streams at once, to 3 different SPDIF outputs. )
I think you can only output one AC3 stream, and that there is only one S/PDIF output.
Given this knowledge of the digital I/O module, I suggest that the pinout *may* possibly be: 1 (tip): S/PDIF output 2 : S/PDIF input 3 : power to digital I/O module 4 : gnd I have not been able to get any S/PDIF signal out of pin 2 (I only have a stereo cable to test with at the moment). I will attempt to test pin 2 as an input at some point.
I think that this card can only output one S/PDIF channel, given the discovery of the required clock settings above, and that Creative's own hardware only gives you access to one output.
Anyway, I don't have access to documentation. From reading around, I believe James has the docs under NDA from Creative Labs. Perhaps James could confirm these suspicions?
Anyway, this is speculation. I'd love to have the docs. I haven't tried to get them. Is it likely/unlikely that I would get them?
I'm currently working on kernel 2.6.22 from Ubuntu. They don't seem to have changed the ca0106 driver, and not much has happened there (for output) in the newer kernels.
Please find attached my current patch, which is only suitable for the purposes of discussion. I need to clarify some things about channel arrangements with those who have the documentation before I begin to try to fix things up. This patch was written with a faulty understanding of the interaction between the channel model and the spdif_enable. I don't know how any of this affects other models in the ca0106 range.
So, I think that before I go any further here, I need some feedback, and access to some documentation would be useful.
Ben Stanley.