ramdisk not created in instructables Embedded Linux Tutorial Zybo

[toastedcpu]

Hello,

I did

PATH=$PATH:~/u-boot-Digilent-Dev/tools/

and  now I am stuck at step 36 Make Uramdisk http://www.instructables.com/id/Embedded-Linux-Tutorial-Zybo/. Please help.

knarf@knarf-VirtualBox:~$ ./u-boot-Digilent-Dev/tools/mkimage -A arm -T ramdisk -c gzip -d ./ramdisk8M.image.gz uramdisk.image.gz
./u-boot-Digilent-Dev/tools/mkimage: Can't open ./ramdisk8M.image.gz: No such file or directory

It created a uramdisk.image.gz file of 64 bytes.

I didn't make a Tutorial directory, so I work in my home directory. The previous step compiled the kernel and put the kernel images in /home/knarf/Linux-Digilent-Dev/arch/arm/boot/.

 

Also, if I use a ramdisk, that means I don't use a filesystem like Linaro. Wouldn't most of the usual Linux directories be missing? (First, I just wan't to finish the tutorial, later I would redo it with Linaro.)

Frank

[toastedcpu]

I finished step 36. On  this forum, mffrac downloaded a pre-built ramdisk8m.image.gz file over at:

https://reference.digilentinc.com/_media/ramdisk8m.image.gz

 

According to this page http://manpages.ubuntu.com/manpages/trusty/man1/mkimage.1.html, it says to use -C instead of -c to specify to compression type.

 

I still don't completely know how much functionality I will get with only a ramdisk.

Frank

[sbobrowicz]

The amount of functionality you get will depend on what gets built into the ramdisk. In the case of petalinux, you are selectively building user space applications, libraries, and scripts into a ramdisk (or, alternatively, a persistent image to flash on the second partition of the SD card). So what features you have is dependent on what you choose.

In the case of the prebuilt ramdisk that the older guides point to, it is a very basic, busybox based system. You will not have much functionality, except for a basic SSH server and some standard console and file commands. Don't expect a desktop or any serious sound support. 

Regarding Linaro, yes, you should be able to flash a prebuilt rootfs image to the second partition of your SD card and modify the bootargs in your device tree to use it. This will provide you with many features over the prebuilt Xilinx ramdisk that the guide is pointing you towards. The features you get depend on the Linaro rootfs "flavor" you choose. I'd recommend alip, which gives you an LXDE desktop and other lightweight features, but isn't as heavy as the gnome-based Ubuntu build. I think you might also get apt-get repo management, but that might only be in the full Ubuntu build. Also, you should note that things might not all work as expected, because those images will all be built against a specific version of the kernel, and you will be using your own kernel. To minimize these issues you should try to pick a rootfs image that targets a version of the kernel that is close to the version you are using. Also, you will need to make sure you manually install any kernel modules you require in order for modprobe to work correctly.

I really feel like a petalinux salesman these days, but I'd recommend making a jump to the petalinux materials. I do believe that running through those older guides is a great way to learn about embedded linux on Zynq, the various components needed for boot, and the build process, but as a practical Zynq/FPGA build environment, petalinux (or yocto) is superior. If you are doing an academic exercise I would say complete it, but then check out the petalinux materials Digilent has for the Zybo. The value it offers should be clear then. It's also 100% free, I'm only pushing it because I think it provides the most productive solution.