[U-Boot-Users] uploading OS over network instead of u-boot do wnloading it from a server.

Wells, Charles Charles.Wells at NielsenMedia.com
Fri Jun 27 15:25:23 CEST 2003


Sorry for the delay, but I've been unexpectedly out of the office.  You make
some good points that I'd like to address.

>> 1. You are assuming that Brian's customers are at least as sophisticated
>> Abatron customers.  Brian's original statement leads me to believe this
>> not so.
>Indeed I think they are. Typing "tftpsrv" (or which other ways  there
>are to start the supplied application "tftpsrv.exe") is IMHO no a big
>challenge. And this is all you need to do.

Typing "tftpd" or whatever is not what I'd worry about.  Many systems are
installed and operated these days by folks with very limited technical
skills.  The problem I see is that 6 months after installation the
customer's MIS group makes network changes and the target device stops
working.  At this point, the operator needs to diagnose the problem and
determine what needs to be done.  No matter how trivial that act of typing
"tftpd" is, the person diagnosing the problem must first determine that the
trivial act is required.  While this diagnosis task is not hard for
programmers and consultants, it may be quite a challenge for the customer.

Now, some might say that the appropriate thing to do in such a situation is
to call MIS or the help desk.  My experience with MIS departments is they do
a good job of networking together Windows (or Solaris or Linux) boxes and
printers, but they want nothing to do with other TCP/IP devices.  The
customer is on their own.  I've seen this problem kill a project.  Remember,
the customer doesn't have to be embarrassed by the triviality of typing
"tftpd", they can just switch to a competitor's product.  They don't even
have to give your sales person a reason.

>> U-boot supports the target-as-client method of downloading but does not
>> support the target-as-server method.  I've used both methods a number of
>> times over the years and both have their advantages and disadvantages.
>Can you please explain the advantages of the  boot  loader  providing
>server function?

It is a unavoidable fact of standard client/server pairs that the client has
a-priori knowledge about the server, the server has no a-priori knowledge
about the client.  If the target is a multicast server, there is NO NETWORK
SETUP AT ALL.  In the case of target-as-client, the client must know at
least the server's IP address (or DNS name).  That knowledge increases the
amount of setup.  Further, during the course of maintenance and expansion,
this information may become invalid.  You can make the required information
as small as possible, but you have to go through the analysis to test
whether this is acceptable to the customer.  My experience is that making
the amount of information used by the client (that can be unilaterally
changed by the MIS department) nil is the best approach.

The key to this is that my download server uses standard UDP over multicast
IP.  This has a number of advantages, including the fact that the download
server is receive-only and has no traditional TCP/IP stack (I won't go into
error control here, but that's taken care of as well).

Another advantage is that this technique can be used very early in the
manufacturing process to load the software (via UDP/IP) that programs the
MAC address (as well as model and serial numbers) into EEPROM.  When this
software is loaded, the target has no IP address or MAC address.  I can even
load many units in parallel on a test rack.

>U-Boot is a Boot Loader, not an OS.
>U-Boot shall be powerful to use, yet simple  in  design  to  make  it
>easily portable to new boards and architectures.
>This means U-Boot will be strictly single-tasking; it  will  not  use
>virtual  memory; it will use polling drivers (versus interrupt driven
>ones) whenever possible.
>U-Boot shall use standard protocols and interfaces whenever possible.

My server-loader meets all of these criteria, except the "powerful to use"
one.  It is not only extremely simple in design but also extremely simple in
implementation (which explains its small size of less than 8k).  It only
does two things, it loads programs in to memory and jumps to that program.
Occum's razor seemed appropriate since we have to strongly avoid updating
the boot code in the field.  Note that my boot code does have a FLASH boot
component that I haven't discussed here.

<> Standard Protocols and Custom Clients

My loader uses standard protocols as well.  It uses UDP over multicast IP.
Since I wanted a passive, receive-only server loader, I rejected TFTP early
because it wouldn't solve all my problems.

You mentioned in a subsequent email to Brian that he would have to write a
custom client.  You are quite correct.  My version of this client is written
as a command-line tool that does the following: 0) create a standard
multicast UDP socket and bind it appropriately, 1) open a file for binary
read, 2) read 1k blocks from the file, 3) prefix a small payload header, and
4) send the block to the socket.  Since we already had a socket library,
this task took an afternoon and the result was just 5-6 pages of C code.
This client hasn't been maintained after it's original creation and testing
(although it has been extended with new features; e.g., alternate binary
file formats, etc.).

It's one thing to say that you have found a boot loader (u-boot) and an
operating system (Linux) for free off the web and made them work.  In fact,
this is very well received by many managers.  But, I do have to develop my
own embedded-target and host applications.  For this I need programmers.
The overhead of writing this custom client program (using standard
protocols) was tiny compared to the entire project.  Further, we were able
to code this functionality into the host-based Visual Basic client used by
our field reps. with very little effort.  This is, I believe one of the
features that Brian is thinking about.

>I'm sorry, but IMHO there is no advantage running  a  server  in  the
>boot loader.

I'm sorry, but IMHO YHO is wrong.  :-)

>Perhaps you might be so kind as to elucidate.

Perhaps I have.

<> Summary

Ultimately, I believe the difference in the two approaches is in where the
control is.  I prefer to view the host as "in control" and the target as
subservient.  It has simply been my experience, over many projects, that
this way works out better.

This whole discussion may not be appropriate on this list.  Since I did this
work as a paid employee, I must honor my employeer's policies that prevent
sharing source code.  I can, however, freely discuss the details and answer
questions  If Brian or anyone else cares to find out more about this
technique, they are welcome to contact me directly.


Charles.Wells at nielsenmedia.com
c.wells at ieee.org

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