Re: Which is freely available Embedded Linux (including tool chains)?

From: Floyd L. Davidson (floyd_at_apaflo.com)
Date: 08/02/05 

Date: Tue, 02 Aug 2005 08:11:29 -0800

"GS" <globalswamy@hotmail.com> wrote:
>Floyd,
>
>If I download Linksys toolchain and then install it and then compile
>it, then can I directly download onto Linksys box, will I be able to
>write onro Linksys box?.

Yes. You can compile the firmware to be *exactly* the same as that
provided by Linksys, or you can modify the source code. In either
case the resulting firmware can be loaded to a WRT54G router using
the "upgrade" functionality on the web interface. It's easy.

>Incase if something wrong happens, then I will
>loose the whole Router,

If you mean when the upgrade process fails (for example the
router will not boot the new firmware), then yes you end up with
a condition commonly referred to as "a brick"!

But, the good news is that Linksys designed several failsafe modes
into the device, and others have been added by various third party
firmware distributions. There are also two hardware modifications
that can be made which greatly simplify recovery too.

The hardware modifications are to add an RS-232 serial port and
to add access to an existing JTAG port. The serial port doesn't
help with the above senario, but it does allow experimenting
with configurations that lock up the Ethernet ports to be
recovered from without a reboot. The JTAG port talks directly
to the CPU, and can recover from virtually any type of firmware
failure, as long as the hardware is functional.

The added features in third party firmware are a watchdog reboot
function and a "boot_wait" feature that allows using TFTP protocols
to be easily initiated during the boot process (it provides a ten
second window when TFTP runs before the system boots).

The Linksys built in features are some default code in the flash
ram that is not normally written to by the firmware upgrade
process, which can be triggered externally to allow a TFTP
process to take over instead of a reboot. (You have to open the
case and short out two pins on the Flash RAM, which gives it a
fault condition that triggers the TFTP process instead of the
normal boot process.)

In other words, you just about *can't* destroy the unit with
firmware upgrades unless you make a real effort at it (the JTAG
port has the option of over writing to the wrong parts of the
Flash RAM, and then only a JTAG connection would be able to
restore it).

>Is there any reference design availble from
>Linksys which I can play with this tool chain?. Thanks in advance.

Well, I'm not sure what you mean. I'll tell you what I did...
I searched eBay for used WRT54G's for sale, and bought a couple
spares! I've got the goodies to add JTAG and the RS-232 port to
one of them, but haven't done it yet. That will be my "test
bed" unit. I have two units in service, and the other spare is
a back up for those. 

-- 
Floyd L. Davidson            <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska)                         floyd@apaflo.com

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