I'm using CP2105 as my standard UART-USB bridge and I am generally very happy with the performance. But there is one little thing which bugs me and degrades the usability quite a bit. After connection a USB cable to the unit it always takes around 20 seconds until I can access the COM port from a PC. I don't have this problem with other interface ICs so I'm wondering why. I'm using the CP2105 in the self powered operation as recommended in the data sheet (see attached schematic) and the OS is Linux with kernel > 4.4.
I hope that someone can help me, thanks in advance!
It takes a long time as well if I leave the device connected and reset the external power supply (can communicate with the CP2105 only after approx. 20 seconds after resetting the power). The VDD and VIO are not connected to VBUS, the PWR_FLAG has a different meaning in my EDA-software (necessary for ERC) and I omitted the ESD protection diodes because the CP2105 is part of a bigger system and the USB cable stays connected all the time.
Is linux maybe trying to detect if there is another device behind the serial port, like e.g. a modem?
I have no idea but I don't think so because different interface ICs (Prolific, FTDI, ...) are working instantly. And if the device is recognized as a virtual com port there is no need for the OS to investigate further what's connected to it AFAIK.