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man pages section 4: Device and Network Interfaces

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Updated: Wednesday, July 27, 2022



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 or 921600. 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 lines.

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 open.

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)) 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 open.


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


USB device I/O error.



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:

SPARC, x86, PCI-based systems

See Also

strconf(1), tip(1), ioctl(2), open(2), termios(3C), usba(4D), termio(4I), ldterm(4M), ttcompat(4M), attributes(7), autopush(8), eeprom(8), 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.