SparkFun Forums

[highlander]

Does anybody know if it is possible to broadcast from USB host to all the connected USB devices? I need to time-synchronize a number of independent devices. USB was my first choice because I could also recharge the devices from the USB bus.

If it's not possible over USB (and I'm beginning to believe it isn't), any other ideas? IP/Ethernet would handle the broadcasting problem, but wouldn't be able to charge off it.

TIA

[wiml]

It's not possible to broadcast a specific message, but every device on the bus should receive the USB start-of-frame packet once per millisecond, and the SOF packet contains a frame counter which is incremented with each frame (it wraps around every 2 seconds or so). So it should be possible for a device to sync on that, to within a few microseconds I'd guess, assuming that the USB hardware in your device can be made to tell you when it gets the SOF packet.

[highlander]

Thanks, wiml, that's a good idea. I'll look into it.

I also stumbled across Power-over-Ethernet last night about 15 min after my post. I'll look into that as well- I don't know how widespread that is, or if it even took hold.

Thanks again for your suggestion.