Zynq AXIS: A complete DMA system

This repo contains all the components needed to set up a DMA based project using the Zynq FPGA from Xilinx. First there is a hardware module called AXIS that connects to a high performance AXI interface port. Second, there is a Linux UIO Driver that exposes the low level AXIS control hardware to the Linux userspace. Third is a userspace library that takes the low level driver interface and provides a more application friendly interface for the user. Lastly there are some example applications to demonstrate the use of the above components.

Hardware

HDL code is kept in the hdl directory, separate from the Xilinx Vivado project directories to make it easier to share code between projects and also to upgrade Xilinx tool versions as needed.

To synthesize the bitstream file one must have the Vivado tools installed and sourced, then simply run the "syn-proj" script from this repos root directory.

./syn-proj

If there is more then one Xilinx project in the syn directory, pass the projects name as an argument into the syn-proj script to chose it. A bash completion script can be found in the util directory to make working with this repos scripts easier.

Linux UIO Driver

This Linux driver has been developed to run on the Xilinx Zynq ARM. It is a userspace input/output driver (UIO) that enables the passing of register values to and from the Zynq FPGA. Userspace libraries/applications use this UIO driver to configure and control the AXIS modules operation. It also controls a contiguous memory area that is used to pass data between the host (PS) and FPGA (PL) sides of the Zynq.

Compile Driver

Kernel modules need to be built against the version of the kernel it will be inserted in. It is recommended to uses the Linux kernel maintained by Xilinx.

git clone https://github.com/Xilinx/linux-xlnx.git

The driver module can be compiling outside of the Linux kernel source tree. A variable 'KDIR' in the Makefile is used to point to the kernel source directory. The default value has it pointing to the default Linux install location for kernel sources. However, if cross compiling or if the sources are in a non-default location the value can be overridden using an exported environmental variable or as an argument passes into the make command.

cd zynq-axis/dev/
export KDIR=../../linux-xlnx
make

or

cd zynq-axis/dev/
make KDIR=../../linux-xlnx

Creating Devicetree

The following AXIS device node needs to be added to the Zynq devicetree to expose the new hardware to the AXIS driver.

axis: axis@43C00000 {
	compatible = "xlnx,axis-1.00";
	reg = < 0x43C00000 0x10000 >;
	xlnx,num-mem = <0x1>;
	xlnx,num-reg = <0x20>;
	xlnx,s-axi-min-size = <0x1ff>;
	xlnx,slv-awidth = <0x20>;
	xlnx,slv-dwidth = <0x20>;
};

Source code for a usable and tested devicetree has been placed int the util directory of this repo. It is an altered version of the 'arch/arm/boot/dts/zynq-7000.dtsi' file found in the linux-xlnx Xilinx repo, master branch commit (da2d296bb6b89f7bc7644f6b552b9766ac1c17d5).

Once the kernel has been compiled for the Zynq, place the altered 'zynq-7000-dtsi' file into the kernel 'arch/arm/boot/dts' directory. Then compile the new devicetree, for the Zedboard run the following command.

make zynq-zed.dtb

Installing Driver

Use of the driver module requires it to be inserted into the running Linux kernel. Once inserted it will automatically create a character device file in '/dev' called '/dev/uio*'. However, the default permissions will not allow non-root users to read/write to the file, nor is the numbering consistent if more then one UIO driver is being used. These problems are overcome by installing the udev rule file found in this projects util directory into the systems '/etc/udev/rules.d/' directory.

sudo cp util/80-axis.rules /etc/udev/rules.d/

To install the module and have it loaded at boot, first install the udev rule as shown above and then follow the below instructions.

sudo mkdir -p /lib/modules/$(uname -r)/extra/
sudo cp axis.ko /lib/modules/$(uname -r)/extra/
sudo depmod -a
sudo modprobe axis

Library

The axis library has to be built and installed on the Zynq before the example applications can be compiled. The library offers a number of generic functions for use in configuring the axis hardware.

cd lib/
make
make install

Applications

The example application demonstrates some simple usage of the AXIS system.

cd app/
make

Acknowledgements

This project was made possible by support from the following people and organisations.

• Teradeep
• e-Lab @ Purdue
• E. Culurciello