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I've been reading about PPS in linux and GPS synchronization.
I stumbled on some sources recommending using a USB GPS, I'm nto quite sure I understand how the interrupt signal is passed through.
The PPS, so the computer can timestamp it very accurately is typically put on DCD in a serial connection. But I don't understand how this is transmit when using USB.
Each USB UART chipset communicates that differently ovet the USB.
And how they do it in detail will not be relevant.
All you need to care is that the USB serial chips have a DCD input pin, and that the USB drivers for those chips provide you with a standard serial port interface so your code running on PC will see modem status events identically, no matter if it is a an actual physical serial port or virtual USB serial interface.
Simply put, all communication between a USB serial chip is done in USB data packets, and just like there are USB data packets that are used to transfer the actual serial data bytes and information related to data bytes such as parity or framing errors, there are USB data packets that indicate changes in the modem status and handshake lines.
