u-boot and root filesystems - Embedded

This is a discussion on u-boot and root filesystems - Embedded ; Hi, I have some questions about u-boot for a project I'm working on. The uP is an ARM9. I am wondering if it's possible to use u-boot to two things in one boot-up: - to create a root filesystem on ...

+ Reply to Thread
Results 1 to 7 of 7

Thread: u-boot and root filesystems

  1. u-boot and root filesystems

    Hi,

    I have some questions about u-boot for a project I'm working on. The uP
    is an ARM9.

    I am wondering if it's possible to use u-boot to two things in one
    boot-up:
    - to create a root filesystem on an SD card (I'm not interested in the
    secure digital functionality)
    - to boot Linux using a Linux kernel image from inside this newly
    created root filesystem

    Another question is how small can a functional rootfs be? I am hoping I
    can get it under 20 MB.

    And a final question is: Is it possible to have a read-only filesystem?
    Or do some things (ie. /dev devices) have to be read/write?

    Thanks, Pete


  2. Re: u-boot and root filesystems


    psommerfeld@gmail.com wrote:
    > Hi,
    >
    > I have some questions about u-boot for a project I'm working on. The uP
    > is an ARM9.
    >
    > I am wondering if it's possible to use u-boot to two things in one
    > boot-up:
    > - to create a root filesystem on an SD card (I'm not interested in the
    > secure digital functionality)
    > - to boot Linux using a Linux kernel image from inside this newly
    > created root filesystem
    >
    > Another question is how small can a functional rootfs be? I am hoping I
    > can get it under 20 MB.


    You can have a bare bone system in 8M or so. But there is not much you
    can do other than starting a custom app.

    >
    > And a final question is: Is it possible to have a read-only filesystem?
    > Or do some things (ie. /dev devices) have to be read/write?


    No, /dev can be read-only, but /tmp amd /var must be writable.

    >
    > Thanks, Pete



  3. Re: u-boot and root filesystems

    linnix wrote:
    > psommerfeld@gmail.com wrote:
    >> Hi,
    >>
    >> I have some questions about u-boot for a project I'm working on. The
    >> uP is an ARM9.
    >>
    >> I am wondering if it's possible to use u-boot to two things in one
    >> boot-up:
    >> - to create a root filesystem on an SD card (I'm not interested in the
    >> secure digital functionality)


    You can use U-boot to store a file system, not to create it.
    Whether you can use your specific ARM9 or not is depending on
    if u-boot supports the SD-interface on your chip.
    If it doesn't then you have to write a driver.

    >> - to boot Linux using a Linux kernel image from inside this newly created
    >> root filesystem


    May beed modifications to U-boot, but I know of people that have done such
    modifications.


    >> Another question is how small can a functional rootfs be? I am
    >> hoping I can get it under 20 MB.

    >
    > You can have a bare bone system in 8M or so. But there is not much
    > you can do other than starting a custom app.
    >


    You can have a complete system with Linux kernel and small file system in 4
    MB
    but you would have very little room for your own application

    >> And a final question is: Is it possible to have a read-only
    >> filesystem? Or do some things (ie. /dev devices) have to be
    >> read/write?

    >
    > No, /dev can be read-only, but /tmp amd /var must be writable.


    Yes, in a way,
    if you use a RAM disk, then the underlying flash image is not writable.

    >
    >>
    >> Thanks, Pete


    --
    Best Regards,
    Ulf Samuelsson
    ulf@a-t-m-e-l.com
    This message is intended to be my own personal view and it
    may or may not be shared by my employer Atmel Nordic AB



  4. Re: u-boot and root filesystems


    psommerfeld@gmail.com wrote:

    > I have some questions about u-boot for a project I'm working on. The uP
    > is an ARM9.


    In answer to most of your questions, please refer to
    which is
    an article I wrote last year on related topics.

    It is irksome to run Linux off a write-protected root filesystem.
    Possible, yes - with tweaking - but it's much easier just to load the
    root filesystem into a RAMdisk and run entirely out of RAM. Faster,
    too.

    As far as memory footprint goes, are you asking about flash storage
    requirements or RAM requirements? You can fit a fully functional Linux
    distribution and applications into 8Mb without difficulty. (The root
    filesystem can be compressed, remember. I've implemented turnkey
    x86-based Linux devices on a 4Mb CompactFlash). I would suggest 64Mb
    RAM, more if you intend to use X. It can be squeezed into less, but
    again it's irritating.


  5. Re: u-boot and root filesystems


    larwe wrote:
    > psommerfeld@gmail.com wrote:
    >
    > > I have some questions about u-boot for a project I'm working on. The uP
    > > is an ARM9.

    >
    > In answer to most of your questions, please refer to
    > which is
    > an article I wrote last year on related topics.
    >
    > It is irksome to run Linux off a write-protected root filesystem.
    > Possible, yes - with tweaking - but it's much easier just to load the
    > root filesystem into a RAMdisk and run entirely out of RAM. Faster,
    > too.
    >
    > As far as memory footprint goes, are you asking about flash storage
    > requirements or RAM requirements? You can fit a fully functional Linux
    > distribution and applications into 8Mb without difficulty. (The root
    > filesystem can be compressed, remember. I've implemented turnkey
    > x86-based Linux devices on a 4Mb CompactFlash). I would suggest 64Mb
    > RAM, more if you intend to use X. It can be squeezed into less, but
    > again it's irritating.


    There are no set rules for flash vs. ram. Very often, it's a
    trade off between costs and limitations. Nowadays, flash
    is sometimes cheaper than ram. There are still many systems
    with limited ram space, but flash is virtually unlimited.

    You can compress everything on flash, but need more ram to
    decompress and run them anyway.


  6. Re: u-boot and root filesystems


    psommerfeld@gmail.com wrote:
    > Another question is how small can a functional rootfs be? I am hoping I
    > can get it under 20 MB.


    I worked on linux project last year, which may give you some
    guidelines... We had a very functional rootfs that fit snuggly into
    4MB (with JFFS2). We kept our app and additional packages (the most
    notable large ones were Python and Qt) in a separate partition in flash
    - that took up a little over 20MB (also JFFS2, and we got better than
    2:1 compression).

    Of course, it all depends on what you want...

    I'm now again working on a linux project, and I've just the other day
    used Busybox to get a minimal rootfs (NOTHING, except init and sh).
    It's only 75K. Of course, the caveat is you need glibc, too, and
    that's 2MB.

    -bri


  7. Re: u-boot and root filesystems

    Thanks everyone for the answers. Very useful info.

    -- Pete

    Brian Silverman wrote:
    > psommerfeld@gmail.com wrote:
    > > Another question is how small can a functional rootfs be? I am hoping I
    > > can get it under 20 MB.

    >
    > I worked on linux project last year, which may give you some
    > guidelines... We had a very functional rootfs that fit snuggly into
    > 4MB (with JFFS2). We kept our app and additional packages (the most
    > notable large ones were Python and Qt) in a separate partition in flash
    > - that took up a little over 20MB (also JFFS2, and we got better than
    > 2:1 compression).
    >
    > Of course, it all depends on what you want...
    >
    > I'm now again working on a linux project, and I've just the other day
    > used Busybox to get a minimal rootfs (NOTHING, except init and sh).
    > It's only 75K. Of course, the caveat is you need glibc, too, and
    > that's 2MB.
    >
    > -bri



+ Reply to Thread