When using XILINX JTAG software like Impact, Chipscope and XMD on Linux, the proprietary kernel module windrvr from Jungo is needed to access the parallel- or usb-cable. As this module does not work with current linux kernel versions (> 2.6.18) a library was developed, which emulates the module in userspace and allows the tools to access the JTAG cable without the need for a proprietary kernel module.
The library uses libusb to access USB devices and the ppdev interface to communicate with parallel cables. The parallel part currently only supports Parallel Cable III mode (and PCIV in PCIII compatibility mode) as the faster PCIV modes use another kernel module which is not emulated by this library. So you are limited to a 200kHz JTAG clock when using Parallel Cable IV with this software. The USB cable is supported at full speed.
Experimental support for FTDI 2232 based devices has been added. They are seen by Impact as a Parallel Cable III. These devices are currently significantly slower than every other supported cable.
The library is called libusb-driver as it was developed to support the USB cable, but later extended to also support parallel cables.
2008-03-26: Xilinx has released their own drivers based on libusb with ISE Design Suite 10.1. To use them, you need to set the environment-variable XIL_IMPACT_USE_LIBUSB to 1 before running the tools. The driver on this page no longer needs to be preloaded if you only used it to access USB cables. Parallel port support still seems to rely on windrvr, which can be emulated by libusb-driver.
Using 32-bit ISE 10.1 on a 64-bit platform: When using the 32-bit JTAG tools from ISE Design Suite 10.1 on a 64-bit machine, the tools will not connect to the cable but output the following error: Cable operation is not supported when running the 32-bit version of the application on a 64-bit platform. To fix this, run the tools with linux32 or preload the newest 32-bit version of libusb-driver. This will lead the tools to believe that they are running on a 32-bit platform and allows them to connect to the cable.
2009-05-31: ISE Design Suite 11.1 now uses Xilinx's libusb-based drivers as default, without the need to set XIL_IMPACT_USE_LIBUSB. If you want to use this driver with ISE 11.1 for USB cables and disable the builtin support for libusb, you now have to set XIL_IMPACT_USE_LIBUSB to 0 (export XIL_IMPACT_USE_LIBUSB=0 or setenv XIL_IMPACT_USE_LIBUSB 0). For parallel cables Xilinx still relies on windrvr. This library works fine with parallel cables and ISE 11.1 with no need for windrvr.
2010-03-15: If you are using newer udev-versions (like the version included in Debian Squeeze and Ubuntu 9.10), then the file /etc/udev/rules.d/xusbdfwu.rules is incompatible with this udev version. The effect of this is that the cable-firmware gets never loaded and the cable led never lights up.
To fix this, run the following command as root:
sed -i -e 's/TEMPNODE/tempnode/' -e 's/SYSFS/ATTRS/g' -e 's/BUS/SUBSYSTEMS/' /etc/udev/rules.d/xusbdfwu.rules
You may have to reboot for this change to take effect.
2010-05-22: Support for ISE 12 is now available in the driver, the presence of "windrvr6" is recognized again. Support for parallel/ftdi-cables is currently limited to existing parallel ports only. So you can't use an ftdi-emulated cable on a non-existing parallel port. Using it on a physically preent port still works.