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The Linux device driver is located in the src/driver directory of the repository. The driver supports device tree and non-device tree initialization with device tree being the default. Non-device tree is somewhat legacy or advanced use cases not supported by device tree. The device driver source code requires two small changes to build in the newer 5.4 .0 rebase kernel for the 2020.1 release of PetaLinux.

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A Vivado hardware build creates an XSA output file(bitstream packaged in XSA) which is then imported into PetaLinux project. After exporting the hardware from Vivado import the new Vivado system into PetaLinux as illustrated below.

$ petalinux-config --get-hw-description <relative path to xsa file>=<PATH-TO-XSA DIRECTORY>

Petalinux Kernel Module

Create a out-of-tree (or "external") Linux kernel module (LKM) to support the XilinxVirtualCable device driver.

$ petalinux-create -t modules -n xvc-driver --enable

Copy some The xvc-driver module recipe you created can be found in the <plnx-proj-root>/project-spec/meta-user/recipes-modules/xvc-driver directory, Copy some of the source code files from the XilinxVirtualCable repository, including the xvc_driver*.c, xvc_driver.h, xvc_user_config.h, and xvc_ioctl.h, into the recipe to build the kernel module in the PetaLinux project (<project>/projects<plnx-proj-root>/project-spec/meta-user/recipes-modules/xvc-driver/files.)

Alter the SRC_URI BitBake recipe vairable in the project at <project>/project-<plnx-proj-root>/project-spec/meta-user/recipes-modules/xvc-driver/xvs-driver.bb recipe file to copy include the required source files into the build area as illustrated below.

SRC_URI = "file://Makefile \
           file://COPYING \
           file://xvc_driver_base.c \
           file://xvc_driver.c \
           file://xvc_driver.h \
           file://xvc_ioctl.h \
           file://xvc_user_config.h \
          "

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Alter the xvc_driver.h source file adding a line to cause LOG_PREFIX to be not used as illustrated in the folllowingfollowing.

#define LOG_PREFIX

Alter the xvc_driver_base.c source file to add conditional code around the mmiowb() function which is not supported with the newer kernel.

 #include <linux/version.h>

#if KERNEL_VERSION(5, 14, 0) >= LINUX_VERSION_CODE
        mmiowb();
#endif

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Create an application in PetaLinux.

$ petalinux-create -t apps -n xvcServer --enable

Copy xvcServer.c from the src/user directory of the The xvcServer apps recipe you created can be found in the <plnx-proj-root>/project-spec/meta-user/recipes-apps/xvcServer directory, Copy xvcServer.c from the src/user directory of the XilinxVirtualCable repository and xvc_ioctl.h from the src/driver directory of the XilinxVirtualCable repository into the BitBake recipe area directory of the PetaLinux project at <project><plnx-proj-root>/project-spec/meta-user/recipe-apps/xvcServer/files.

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Alter the BitBake recipe of the application at <project-spec><plnx-proj-root>/project-spec/meta-user/recipes-apps/xvcServer/xvcServer.bb to copy the source files into the build area as illustrated below.

SRC_URI = "file://xvcServer.c \ 
           file://xvc_ioctl.h \
           file://Makefile \
          "

PetaLinux Device Tree

DEPENDS = "\
    xvc-driver \
    "

PetaLinux Device Tree

The device tree node for the Xilinx Debug Bridge IP in the PetaLinux generated device tree (pl.dtsi) does not match the compatibility string for the device driver. Alter the system-user.dtsi device tree of the PetaLinux project in <plnx-proj-root>/project-spec/meta-user/recipes-bsp/device-tree/files to alter the compatible string to match that driver as illustrated below.

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PetaLinux Image Build

Build the Linux image.ub in Petalinux PetaLinux System Images as illustrated below.

petalinux-build

Build the boot.bin , When the build finishes, the generated images are stored in the <plnx-proj-root>/images/linux or /tftpboot directories.

$ petalinux-build

Package the BOOT.BIN image with all the boot components including the FPGA bitstream. From the <project><plnx-proj-root>/images/linux directory the boot image is built as illustrated below.

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the boot image is built as illustrated below.

$ petalinux-package --boot --format BIN --fsbl <plnx-proj-root>/images/linux/zynqmp_fsbl.elf --u-boot <plnx-proj-root>/images/linux/u-boot.elf --pmufw <plnx-proj-root>/images/linux/pmufw.elf --fpga <plnx-proj-root>/images/linux/system.bit --ubootforce

Running The Prototype

Starting The Software

The following steps assume Linux has booted on the embedded target and the network is functional with respect to a valid IP address and the host computer running Vivado is on the same network (subnet). From the running target the device driver should be started as illustrated below.

root@xilinx-zcu102-2020_1:~# modprobe xvc-driver 

The following console output illustrates the expected output when the driver is working.

root@xilinx-zcu102-2020_1:~# modprobe xvc-driver

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[   21.370940] xvc_driver: loading out-of-tree module taints kernel.

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[   21.377673] Starting...

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[   21.380476] Created device xilinx_xvc_driver

From the running target the server application should be started as illustrated below.

root@xilinx-zcu102-2020_1:~# xvcServer &

The following console output illustrates the expected output when the server is working and ready to use.

root@xilinx-zcu102-2020_1:~# xvcServer &

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INFO: XVC driver character file: /dev/xilinx_xvc_driver

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INFO: debug_bridge base address: 0xA0000000

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INFO: debug_bridge size: 0x10000

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INFO: debug_bridge device tree compatibility string: xlnx,xvc

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INFO: To connect to this xvcServer instance, use url: TCP:xilinx-zcu102-2020_1:2542

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In the past there have been issues where the clock(s) to the PL could be shut off so that the ILA does not function. This can be prevented by adding a kernel parameter to the Linux boot arguments in the device tree. Edit the <plnx-proj-root>/project-spec/meta-user/recipes-bsp/device-tree/files/system-user.dtsi file in the PetaLinux project and alter the boot arguments to add “cpuidle.stopoff=1” as illustrated below. For more details refer AR# 69143

    chosen {
            bootargs = " earlycon console=ttyPS0,115200 clk_ignore_unused root=/dev/ram0 rw cpuidle.stopoff=1";
            stdout-path = "serial0:115200n8";
    };

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If the output of the device driver does not include all the lines (as illustrated below) then the device tree for the Debug Bridge may not be up to date as specified in the steps. The driver can be inserted into the kernel but not find any compatible driver so that it is not functioning even though it is in the kernel.

root@xilinx-zcu102-2020_1:~# modprobe xvc-driver

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[ 21.370940] xvc_driver: loading out-of-tree module taints kernel.

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[ 21.377673] Starting...

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[ 21.380476] Created device xilinx_xvc_driver

Hardware Manager And JTAG

Vivado hardware manager can be used to connect to the target using JTAG rather than the network connection such that the server may show an error when it is attempted as shown below.

root@xilinx-zcu102-2020_1:~#

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connection accepted - fd 5

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setting TCP_NODELAY to 1

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invalid cmd 'E'

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connection closed - fd 5

Conclusion

There are many ways to use the Xilinx Virtual Cable other than the method shown above and this page was only intended to show principles to help users understand how the system works.

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