20151126-1：XMOS的英国工程师关于休眠和自动恢复的答复

关于XMOS “更合适的是侦测到有音乐数据时，自动恢复播放模式” 这种功能，说明如下：

“As with most things in USB, it iscontrolled by the host. After 3ms of inactivity, the device enters suspendmode.We support suspend mode already as part of theUSB spec (and resume of course) but currently the power saving is minimal whenin that state. There has been some work (using external circuitry)to reduce this down to microamps, but it’s still under development.

However, I do not think this will help. Suspendmode is controlled by the host. Suspend is normally issued when the hostsleeps/hibernates or is shut down.It is not normalfor the host to issue a suspend when streaming stops. This istechnically feasible, but a host driver would need to be written to detectstreaming stop and issue a suspend to the USB device in this case.

I think the best we can automatically do islook at optimising XUD power and shutting down the audio subsystem whenstreaming stops (stop MCLK for example). This will need some work, but I don’tthink we can save too much.

So in summary, automatic wake up onstreaming start would either require the host driver to be modified to issuesuspend/resume, or it needs USB (XUD) to be kept alive to see that streamingshould start again. The latter will still need around 200mW as a first guess.”

总之，建议按照你们的第一个场景“当没有音乐播放时，产品进入休眠模式，此时可以用开机键恢复播放模式” 来做设计。