Re: [ECOS] Re: RAM vs. ROMRAM question

[Nick Garnett <nickg at ecoscentric dot com>]

 Grant Edwards <grante@visi.com> writes:

> What does being a "ROM Monitor" have to do with startup mode?
> Shouldn't Redboot be able to provide services to applications
> either way?  In both cases it's running from RAM, so I don't
> see why the distinction is made.

Startup type and monitor functionality are decoupled as you
suggest. However the configuration of a particular target may not
allow certain combinations.

Many targets do have a version of RedBoot that will run from RAM. It
is necessary in targets that use ROM RedBoot to allow RedBoot to be
replaced. If it doesn't work for a particular target, then either it
has been disabled, or the configuration is broken and has never been
tried, because it is simply not needed.

Using a RAM RedBoot to load RAM applications will not work since
RedBoot would load at exactly the same address as the applications,
with obvious bad consequences. If this functionality is needed then
RedBoot needs to be relocated. Since the main reason for doing this is
often to allow RedBoot to be loaded via JTAG, then targets that
support this usually have a JTAG startup type to support this. The
same startup type supports the running of full applications via JTAG
too.


-- 
Nick Garnett                                     eCos Kernel Architect
http://www.ecoscentric.com                The eCos and RedBoot experts


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