[Qemu-devel] [PATCH] USB serial device

[Samuel Thibault]

Hello,

Samuel Thibault, le Fri 11 Jan 2008 00:23:12 +0000, a écrit :
> I would like to implement support for braille devices, and for this I'd
> need to first implement a USB serial device (FTDI chip).  Has anybody
> worked on that already?

Ok, was easier than expected, Here is a patch. The serial support is
incomplete however because qemu still lacks support for flow control and
modem lines.

You will notice in tty_serial_init that I made the baud values more
relaxed. This is because with divisor/baud conversions, things never get
exact, so we need to be laxist with the value. For instance here with
FTDI, the base divisor is 48000000/2, so for 57600 bps the guest needs
to choose between divisors 416 and 417, which bring to either 57692bps
or 57553bps but not exactly 57600bps. It happens that Linux chooses
divisor 416, hence 57692bps. Of course, the higher the speed, the worse
things get. The 1.1 factor is the smallest factor I could find between
usual bps values, notably B110, B134 and B150.

Samuel

patch-qemu-usb-serial
Description: Text document