usbftdi - FTDI USB to serial converter driver


#include <fcntl.h>
#include <sys/termio.h>


The usbftdi driver is a loadable STREAMS and USBA (Solaris USB
Architecture) compliant client driver that provides basic asynchronous
communication support for FTDI USB-to-serial converters. Serial device
streams are built with appropriate modules that are pushed atop the
usbftdi driver by the autopush(8) facility.

Application Programming Interface

The usbftdi module supports the termio(4I) device control functions
specified by flags in the c_cflag word of the termios structure, and by
the IGNBRK, IGNPAR, PARMRK, and INPCK flags in the c_iflag word of the
termios structure. All other termio(4I) functions must be performed by
STREAMS modules pushed atop the driver. When a device is opened, the ,
ldterm(4M) and ttcompat(4M) STREAMS modules are automatically pushed on
top of the stream, providing the standard termio(4I) interface.

Use device logical names /dev/term/[0-9]* to access the serial ports for
a dial-in line that is used with a modem.

Use device logical names /dev/cua/[0-9]* to access the serial ports for
other applications. These names are also used to provide a logical access
point for a dial-out line.

Device hot-removal is functionally equivalent to a modem disconnect
event, as defined in termio(4I).

Input and output line speeds can be set to the following baud rates: 300,
600, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200, 230400, 460800,
921600, 2000000, or 3000000. Input and output line speeds can not be set
independently. For example, when the output speed is set, the input speed
is automatically set to the same speed.

Soft Carrier Capabilities

Many devices that use this USB serial interface component are not, in
fact dial-in lines connected to carefully configured RS-232 modems. They
are often intelligent peripherals whose manufacturers want to present a
serial port interface to application software. Some applications use only
three wire connections, or are otherwise somewhat casual about the state
of the Carrier Detect (electrical) signal, and the other modem control

The configuration file delivered with this driver, usbftdi.conf,
acknowledges this by setting the driver property ignore-cd to 1. This
enables soft carrier mode where the kernel does not block opens waiting
for DCD to be asserted.

This behavior also matches the default ignore carrier detect behavior of
the onboard serial ports of machines that have them. See eeprom(8) for
further details.

The hardware carrier behavior (the driver's internal default) can be
selected by either unsetting (commenting out) the ignore-cd property, or
by setting the value of the property to zero.

More sophisticated selection of which devicesl ignore or obey the DCD
signal can be effected using port-%d-ignore-cd properties.

Dial-In and Dial-Out Support
A related feature is available for traditional usage that enables a
single tty line to be connected to a modem and used for incoming and
outgoing calls. By accessing through device logical name /dev/cua/[0-9]*,
you can open a port without the carrier detect signal being asserted,
either through hardware or an equivalent software mechanism. These
devices are commonly known as dial-out lines.

A dial-in line can be opened only if the corresponding dial-out line is
closed. A blocking /dev/term open waits until the /dev/cua line is
closed, which drops Data Terminal Ready, after which Carrier Detect
usually drops as well. When the carrier is detected again with the
/dev/cua device remaining closed, this indicates an incoming call and the
blocking open seizes exclusive use of the line.

A non-blocking /dev/term open returns an error if the /dev/cua device is

If the /dev/term line is opened successfully (usually only when carrier
is recognized on the modem, though see Soft Carrier Capabilities section
of this manual page), the corresponding /dev/cua line can not be opened.
This allows a modem and port to be used for dial-in (enabling the line
for login in /etc/inittab) or dial-out (using tip(1) or uucp(1C)) when
no-one is logged in on the line.


An open() fails under the following conditions:

The unit being opened does not exist.

The /dev/cua (dial-out) device is being opened while the
/dev/term (dial-in device) is open, or the dial-in device is
being opened with a no-delay open while the dial-out device is

The unit has been marked as exclusive-use by another process
with a TIOCEXCL ioctl() call.

USB device I/O error.



32-bit x86 ELF kernel module


Kernel module configuration file


64-bit x86 ELF kernel module


64-bit SPARC ELF kernel module


Dial-out tty lines


Dial-in tty lines


See attributes(7) for a description of the following attribute:

|Architecture | SPARC, x86, PCI-based systems |


strconf(1), tip(1), uucp(1C), autopush(8), eeprom(8), ioctl(2), open(2),
termios(3C), usba(4D), termio(4I), ldterm(4M), ttcompat(4M), eeprom(8),


In addition to being logged, the following messages might appear on the
system console. All messages are formatted in the following manner:

Warning: device_path usbftdiinstance num): Error Message ...

Device was disconnected while open. Data may have been lost.

The device has been hot-removed or powered off while it was open and
a possible data transfer was in progress. The job might be aborted.

Device is not identical to the previous one on this port. Please
disconnect and reconnect.

The device was hot-removed while open. A new device was hot-inserted
which is not identical to the original device. Please disconnect the
device and reconnect the original device to the same port.

Device has been reconnected, but data may have been lost.

The device that was hot-removed from its USB port has been re-
inserted again to the same port. It is available for access but data
from a previous transfer might be lost.

Cannot access device. Please reconnect.

This device has been disconnected because a device other than the
original one has been inserted. The driver informs you of this fact
by displaying the name of the original device.

The following messages might be logged into the system log. They are
formatted in the following manner:

device_path usbftdiiinstance number): message ...

Input overrun.
Data was lost.

August 13, 2021 USBFTDI(4D)