There are currently two other drivers available; the ftdi_sio driver
and the libftdi0 driver. See the FTDI site for currently available drivers.
Using the SDR-IQ on my machine, I found the ftdi_sio driver limited to
about 70k samples per second. The libftdi0 driver was capable of
about 100k SPS. The ft245 driver works fine at 110k SPS and I
don't know its upper limit yet. The other drivers may be
preferred for applications other than SDR. The ftdi_sio driver
emulates a terminal with full termios capability, and the libftdi0
driver offers bit-bang capability.
This document describes how to install the ft245 driver on a modern
Linux system. But if you are using Linrad, see below because
Linrad has its own way of installing the driver.
My computer is an Asus AMD dual core running Debian stable, kernel
2.6. USB drivers depend on the Hotplug, Udev and Modules
subsystems of Linux, and these are evolving rapidly. So the exact
description of ft245 installation will probably be different for you,
and will almost certainly be different in the future. Therefore I
am giving more than the usual amount of explanation so you can adapt
this to your needs. Besides, it is fun to know how things work.
The first step is to install some packages you may not have.
All drivers are compiled for a specific kernel version, and that
requires the kernel header files. Use your package or RPM
software to install these packages plus any dependencies:
I use Synaptic on Debian. The command line version is aptitude
(use "man aptitude"). Be sure to install the headers for the
exact version of Linux you are running. This is a good time to
become familiar with the uname -r command:
$ uname -r
It gives the version of the kernel that is running on your
computer. It is used in scripts that compile modules, and it
appears in directory names such as "/lib/modules/2.6.18-5-686".
When you upgrade to a new kernel, you must re-compile the ft245 driver
for that kernel. The old version will not even be found, and may
not work anyway. The package names above are top-level packages
that depend on the most recent version of Linux. That means that
when a newer version of Linux comes out, the most recent headers are
downloaded too. If everything works right, you should have a
directory /lib/modules/VERSION/build, where VERSION is the exact output
of "uname -r". Always use your own version, and not
"2.6.18-5-686" as you follow this document.
Create a directory for the ft245 driver files, such as
/home/jim/ft245. Download the latest driver version from the ft245 site
into that directory. The file is a .tgz file, so:
tar xf ft245_driver-lin26-203.tar
Then from a terminal in that directory, compile the ft245 driver by
entering "make". If you get the error message
ft245.c:195: error: unknown field 'owner' specified in initializer
then comment out line 194 through 196 by inserting "//" at the start
of the line. If you get a lot of error messages, don't panic; you
are probably just missing another header file. Look at the
beginning of the error messages for something like "can not find
foobar.h". That means you need the file foobar.h but you don't
have it. Find out which package provides that file, and install
it. I go to Debian's
package page and search for the file name "foobar.h". Do not
search package names and descriptions; search for files. Install
the package that contains foobar.h and try again.
If this all works, you will have your
driver file ft245.o and ft245.ko. The correct file on my system
is ft245.ko, but older versions of Linux use ft245.o. Look in
/lib/modules to see which one you need. Or try loading it with
modprobe (as root). You will get an error message if you load the
Copy the correct driver (you will need to be root) to a
suitable location corresponding to your kernel version:
cp ft245.ko /lib/modules/2.6.18-5-686/kernel/drivers/usb/serialNext you must run depmod to create various databases:
Now if you plug in (for example) the RfSpace SDR-IQ, the ft245
driver should be loaded. Verify this with "lsmod". You can
load the driver by hand with "modprobe ft245" (you will need to be
You can remove the driver (root again) with "rmmod ft245".
If you have trouble, try looking at kernel messages with
dmesg. The kernel will add messages as USB devices are plugged
and unplugged. Look at the newest messages at the end of dmesg
$ dmesg | tail -20
Your ft245 driver is now installed, but we are not done
yet. The ftdi_sio driver is included with Linux, and so you have
two drivers that claim to handle the SDR-IQ (or other) hardware.
Even if things seem to work, they may fail in the future if the wrong
driver accidentally gets loaded first. This is where the modinfo
command comes in handy. You must be root to use modinfo.
# modinfo ft245
author: Robin Cutshaw, spam
description: USB Driver for FTDI FT245 chipset
vermagic: 2.6.18-5-686 SMP mod_unload 686 REGPARM gcc-4.1
All this output is useful information, but look closely at the lines starting with "alias". The ft245 driver is advertising that it is a driver for the USB devices with vendor ID 0x0403, and product ID's 0xF728 and 0x6001. We can look up these ID's and find that the vendor is FTDI. If you enter "modinfo ftdi_sio" you will see that it claims to support the same two devices (as indeed it does). To make sure that the ft245 is selected as the RfSpace driver create the file /etc/modprobe.d/sdriq (or other name of your choice) with this contents:
alias usb:v0403pF728d*dc*dsc*dp*ic*isc*ip* ft245
alias usb:v0403p6001d*dc*dsc*dp*ic*isc*ip* ft245
Note that some systems use modprobe.conf instead of
modprobe.d. So what is happening? The vendor and product
ID's are coded
into the USB hardware device. When the device is plugged in, the
system looks for the name of a driver. The "alias" lines in the
files in modprobe.d provide the name of the driver to use. If no
alias line is found, then the aliases coded into the driver files
themselves are used.
Now if you unplug your SDR-IQ (or other hardware), remove the ft245
and ftdi_sio drivers with rmmod (be root), and plug the hardware back
in, you should see that the module ft245 is loaded (lsmod). When
ft245 loads it will create
the file /dev/ftdi2450, so check to see that the file exists. If
the ftdi_sio driver is in
use, it creates the file /dev/ttyUSB0. These files in /dev are
special files that provide communication with the driver. To use
the driver, you open the file in /dev that the driver created.
But on my computer the file /dev/ft2450 is create with rw-rw----
permissions, and with owner root and group root. That means I
can't open it unless I am root. I hope by now everyone knows that
you never require users to run as root. So create the file
/etc/udev/rules.d/local.rules with this contents:
# Additional rules for this computer:
# USB devices
KERNEL=="ft245?", MODE="0660", GROUP="dialout"
The Linux udev subsystem creates the files in /dev that are needed
from time to time. The above rule specifies that files named
that is, "ft245" followed by one additional character, should be
with "0660" permissions (rw-rw----) and with a group name
"dialout". I chose "dialout" because I am a member of it already,
and that is the group of /dev/ttyUSB0 on my computer. Check what
groups you belong to for other possibilities (maybe the plugdev or
audio groups work for you). An alternative would be to change the
MODE to 0666, meaning read/write by anyone, and removing "GROUP".
Now unplug your hardware and plug it back in. You should have
/dev/ft2450 with proper permissions. By the way, if you have
multiple hardwares, they have names ft2450, ft2451, ft2452, ....
If you downloaded Linrad and ran "make sdr14", then the ft245 driver
is installed in a different way. It is started with the SYS5
startup scripts in /etc/rc0.d, /etc/rd1.d, etc. In these
/etc/rc*.d directories are links to the file
/etc/linrad/usb_sdr14. The usb_sdr14 program loads and unloads
the driver, and creates the file /dev/linrad_ft245 to access it.
I am not sure about interference from ftdi_sio.
There is nothing wrong with this, and it will work on many Linux
flavors including older systems. But if you want to install ft245
as described above, then don't use "make sdr14". If you already
have the usb_sdr14 links in /etc/rc*.d, remove them (carefully) and
remove /etc/linrad. You can check the Linrad Makefile to see
exactly what you need to remove. Then in lsetad.c change the
define for SDR14_DEVICE_DRIVER from "/dev/linrad_ft245" to
"/dev/ft2450". I have not tested this, but it should work.
Linrad also has its own version of ft245.c, so maybe you want to
install that version of ft245.ko.
If you are writing code for the ft245 there are a few things you
should know. The receive buffer is not a circular buffer.
Characters from USB are appended to a 64k byte buffer, and the buffer
write position is reset to zero only when the buffer is empty. So
you must be sure to read all available characters before the buffer has
a chance to overflow. Also, a read of greater than 64k is
considered an error, so you must limit a read request to 64k maximum.
The data from the SDR-IQ is a byte stream with the data length and
type coded in the first two bytes. You read a block by decoding
these two bytes and then reading the rest of the block using the
length. But if any bytes are lost, you will read into the next
block, and the two byte header will actually be data from a subsequent
block. This causes the read process to go out of sync. It
is easy to lose bytes by starting another program, moving windows
around on the screen, etc.
To detect a loss of synchronization, I consider all lengths less
than 2 (the length includes the two-byte header) and greater than 50
(large data blocks have a special length of zero) to be an error.
Assuming the SDR-IQ is running and returning data blocks, I try to
resynchronize by looking for the data block start 0x00, 0x80.
This was written by Jim Ahlstrom, N2ADR, in the hope that it would
be useful. You can write me at user name jahlstr computer gmail.com. I am using the ft245 driver in one of my SDR
to Robin Cutshaw for the driver, and to Lief
Asbrink, SM5BSZ, for Linrad
and his many contributions to all things SDR.