Low noise, low power, fixed freq. for stable usb and toslink audio streamer

Help and Support Vero V
1

Hi,
I would like to get the most stable Toslink out & 2.0 usb audio out signals to connect to a external powered DAC with the most stable signal.
I have a spare 1/1.2A max linear power supply that I’d like to try with the Vero for lowest internal switching noise. I’ve thought of fixing the CPU cores frequency to a value such as 667 MHz (and the VPU aswell if supported) so the voltage regulators work as little as possible and the clock signal is stable for the Toslink LED transmitter and/or USB bus signal.
Would 1.2A be enough for stable H264 1080p 60Hz hardware decoding and operation? Do you recommend? I could set an userspace governor with a fixed frequency at starup on rc.local or a early service.

I’d be using at first Toslink out and a USB3 fast pendrive as source on USB2.0 port for lowest noise. I could as well play from eMMC memory if space is enough so external USB ports aren’t used for less interference.

I’d also use USB2.0 audio out to the external DAC powering with another LPS so less noise is transferred through the USB cable. I’d use either toslink or USB that yields better sound quality. Do you have experience using toslink and USB through the Vero? Hope I’m not crazy enough :wink:

2

All I can say is I’ve used both. USB to a £50 DAC and Toslink to my AVR. I’ve not experimented with smoother PSUs. Let your ears be the measure.

Vero V doesn’t pull more than 1A normally. If all peripherals have separate power supplies you should be fine. Except beware of ground loops.

3

Good. Could you please share filesystem nodes for VPU and CPU core frequency control?

Also, if possible, it would be useful to query instant power/current consumption.

I’ve tried with the 1.2A max linear power supply but it doesn’t get to home screen, it gets on a reboot loop. I have only one pendrive connected, with default settings. That’s why I aimed to lower the CPU frequency, to lower the current, although maybe I’m on the limit.

By curiosity, ¿does it accept input voltage above 5V?

4

I don’t know, I’ve never played with those.

Well I just booted a Vero V with a pendrive connected and it didn’t draw more than 1A while booting.

No. I think there’s a limiter that cuts out if the voltage hets too high.

10

cpu_freq and governor can be adjusted via sysfs
Same for GPU

VPU clock is set by kernel on a codec basis.

I don’t recommend adjusting any of these.

11

Thanks Sam for your advice.
My objetive would be aiming for a stable playback CPU/VPU clock frequency for a clean USB bus audio out, with the least noise from the voltage regulators. I plan on a low noise 5V-2A linear power supply to help on this.
I did a test and fixed the CPU cores to 1.2 Ghz and H264 reproduction stability was fine. I didn’t try with the VPU. My intention is using eMMC for media (or even a SD card) and discard USB for lowest source noise.
I realise that playback frequencies are stable, so there’s no need for a fixed value. Perhaps lowering the CPU scaling max freq to a lower value than 2 GHz, but I’m not sure whether it’s needed for video performance.
I also wonder about deep C-states convenience for playback USB voltage stability, for example disabling C6 so cores they don’t go in an out of sleep (restrict to C1 or C2), if temperature is not a concern.

As for WUXGA refresh timings, I am waiting for Barco to relase a firmware update to my projector with a EDID that includes compatible DTDs for these timings and deep colour support, so the Vero V has the best way to adjust.