Synchronous usb audio using internal application PLL

[Ross]

XMOS has traditionally concentrated on asynchronous usb audio for a few reasons such as quality and ability to synchronise to an external digital stream.

However, there may be reasons why you may wish to use synchronous mode. Perhaps because a limited USB host (like a TV) doesn't properly support async or because you want to plug multiple units into one host and have them all synced etc.

Previous support for sync mode required an external clock multiplier (i.e. cirrus cs2100), however, there is some early code to support sync mode with the internal PLL on these branches (keep the rest of code the same as the latest release)

https://github.com/xmos/sw_usb_audio/tr ... nc_app_pll
https://github.com/xmos/lib_xua/tree/ex ... nc_app_pll