This is a driver for the Cyclades PC-300, a family of PCI cards with synchronous serial interfaces (T1, E1, etc.) on them. The present Linux kernel source contains a very old (version 3.23) and not especially functional version of this, and the version (4.1.0) distributed with the cards doesn't work with changes in the kernel HDLC layer after 2.6.3, or on non-x86 platforms for pointer size and memory alignment reasons. In early 2005 I found myself trying to connect a Sun Ultra 10 to a T1 circuit using one of these cards, and ended up porting the current driver version (4.1.0) distributed by Cyclades to run on recent kernel versions and this hardware. This has only been tested with a single T1 circuit on a sparc64 platform, but I believe it will work with the other cards and on other platforms.
This driver is available as a patch against kernel version 2.6.16.11. To install the patch, run patch -Np1 -i <path_to_patch> from the root of the kernel source tree.
It is also available as a free-standing tarball. To install the tarball, run bunzip2 < <path_to_tarball> | tar -xvf - from the root of the kernel source tree.