Hi everyone, It's several years since I've posted in this group. Lately I've been brought back into Windows audio matters. I know this is a software-focused group for audio, but many of you may know a thing or two about USB protocol messages to a USB audio device. Here is the situation, we're dealing with a C-Media audio device CM6206, using MS usbaudio.sys driver. The C-Media chip is sitting behind a NEC USB2.0 hub that's connected to a NEC USB2.0 host controller, itself connected to a PLX PCIe switch. Using Windows XP SP3, the driver installs fine, typical audio playback works fine (directsound or wave output). However, when we concurrently enable video and audio, for example playing back a movie in full screen, with no hardware video decoding, we lose audio after "a while", and can't get it back. However, the Windows default sounds (for example system beep or logoff sounds) are still working fine. The interval of time before we lose the audio varies with the graphics activity in the system, as well as with various systems of various speeds, so it can take 5mins or it can take 1 day. We tried the C-Media driver as well and got the same symptom. We also tried different USB audio chip manufacturers (including TI) to no avail. So we looked at the USB transactions on the USB bus going into the USB audio chip. We note a series of OUT transactions followed by IN transactions, usually containing a "NACK" message. This goes on for as long as the audio plays back fine. Then we get a series of OUT transactions with no corresponding IN transactions, then we get a Reset event. Can anybody put light on this scenario, explain the Reset event, or suggest further debugging steps? Thank you very much. Martin Gagnon Matrox Graphics
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