Brooklyn/gnuk/chopstx/example-usb-serial

This is an application example using ST Nucleo F103 board.

SB62 and SB63 should be soldered to connect PA2 and PA3 to CN10
connector.

ST-Link/V2's TX and RX are disconnected (by removing SB13 and SB14).

Smartcard can be connected, by using USART3_TX for I/O and USART3_CK
for CLK, PB6 for Vcc, PB8 for Vpp, and PB9 for RST.


NOTE:

Using the USB CDC-ACM for serial communication is a kind of wrong,
because it's designed for modem; In the protocol, we have no way to
control the CTSRTS signal.

TIOCGICOUNT


TODO:
* Use of DMA for serial communication
* RS-232 support: GPIO with DTR (out), DCD (in), DSR (in), RI (in)
* serial config setting of CTSRTS?
  By vendor specific control?
* stats report control
  By vendor specific control?
* Half-duplex support
* Support of other communication mode: IrDA, etc.