I have application on Windows-host that connects to board-device via RS232 with full handshake (RTS, CTS, DTR). I want to replace the RS232 with USB now. I use board with embedded linux and USB device (g_serial) module. I get all the data on terminal both sides, but application can't handle it (lack of handshake signals). How is it possible to handle it ? (Host or device side) Maybe there are some handshake "emulators" that cares about handshake on PC-host side ?
BR Bartlomiej Grzeskowiak
I looked through the kernel (originally 3.8, later 4.11) source code for the g_serial driver in the Linux kernel, to see if it implements the API to control the hardware handshaking lines on the Linux-side API (/dev/ttyGS0). E.g.:
#include <unistd.h>
#include <termios.h>
int fd;
int status;
...
ioctl(fd, TIOCMGET, &status);
status |= TIOCM_DTR;
ioctl(fd, TIOCMSET, &status);
It looks as though the driver has no support for it. In drivers/usb/gadget/function/u_serial.c, see struct tty_operations gs_tty_ops which doesn't define the .tiocmset or .tiocmget members which would normally be needed to support the above code.
So I think the driver would need to be improved to add this support.