I have an XMOS based DAC (XMOS 384K/32bit PCM5102 DAC USB) fed from a Raspyfi 1.0. The Raspyfi and DAC have their own independent HQ regulated 5v power supply off the same transformer.

When I fist power on the Raspyfi/DAC I usually find the DAC does not come on (no indicator leds on the board). If I power off then back on again invariable the Raspyfi and DAC boot up fine.

Runnning lsusb shows the DAC as present (Bus 001 Device 004: ID 20b1:0002 XMOS Ltd) when the boot up is fine. However when the the DAC does not come on lsusb does not show the 4th device. So the USB device is not even being seen.

When in the state of the DAC not being present, if I do a sudo reboot the DAC still does not show.

Otherwise the DAC is working fine so I don't think the DAC is faulty. I am wondering if it is a timing issue. Shoudl the DAC be powered before the Raspyfi or visa versa,

Has anyone else come across this problem?