Is there a standard way to retrieve Time-of-day onto a "dongle" connected to a computer over USB?
My IoT device is connected over USB for power, but has data connection pins (for firmware download). I would like to get TOD w/o software on computer and am not sure how this is typically done.
I understand I'm out of luck if the user connects my device to a power-brick, but if to a computer, how's the best way to grab the time?
Thanks,
Kent
Is there a standard way to retrieve Time-of-day from a "dongle" connected to a computer over USB?
Not that I'm aware of, and a quick scroll through USB device classes brings up nothing.
I would like to get TOD w/o software on computer and am not sure how this is typically done.
You would need some time source – NTP if you have internet connectivity, or you need to have GPS receiver, or you could have a time-standard receiver (in central Europe, that'd be DCF77). Anyways, nothing that cares about whether it's connected via USB.
I understand I'm out of luck if the user connects my device to a power-brick, but if to a computer, how's the best way to grab the time?
You're conflating things here. A computer is not a USB device, it's a host. Your device can't "query" the computer – it needs the computer to query it to be able to respond. So, that computer would need a driver for your device. To get the computer time to your device, you need that driver (or a program using that driver) to update the device time from the computer.
So, I think what you want is plain impossible.
My IoT device is…
(emphasis mine)
Your Internet of Things device probably has an internet connection, so it can use the internet to query time (e.g., via NTP, but if you can live with a bit of uncertainty / inaccuracy, also via other methods like reading a HTTP response's date: header. Either way, the device would need to know the time zone it is in (that does not automatically follow from e.g. its IP address, at all), and how to convert a UTC time to its own timezone, if you need time stamps to be in local time. (if this is just about logs, you don't.)
Since the A in "Internet of Things" stands for "naming Accuracy", it might be that your IoT device is just part of some network where it's individually addressable. No problem – just propagate time information through that network. Quite likely, that is already implemented in some form if that is a wide-area wireless network.
Is there a standard way to retrieve Time-of-day from a "dongle" connected to a computer over USB?
Yes, there is. Sort of. In fact, there are two major ways that have relatively low "friction" from user perspective.
The "dongle" needs to present as if it were an Ethernet adapter over USB. Which exact class will depend on what OS you're targeting.
When connected to a computer, the dongle will appear in the network manager as a yet another ethernet adapter. By default, link-local IP addresses will be used on both ends of the link.
A billboard class device is recognized by most OSes and shows up a notification with a URL. That URL can point to the local name (mdns) of the dongle. User experience:
You also need to enable NTP (network time protocol) service on the machine. The dongle can then query the time on the computer. The computer's time service will be synchronized with other, more authoritative, time references on the internet (usually).
ntpd service, e.g. from console with service ntpd start command.Using webusb from a web page or a web application, access the dongle from the browser and send the time to it. Which protocol you'd be using for this is up to you. It can be fairly low level. For Windows compatibility, the dongle should expose the descriptors for a winusb device. That way, Windows will load the generic winusb.sys driver for the device automatically. Devices that use this driver can be accessed via webusb on Windows.
A billboard will also offer a notification with a link to click on.
User experience:
