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Re: Re: RAM vs. ROMRAM question
Grant Edwards wrote:
On 2006-10-30, Nick Garnett <nickg@ecoscentric.com> wrote:
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.
That's odd, I do it all the time. ;) I've been shipping
products for years where RedBoot runs from RAM as a "ROM
Monitor" and loads applications into RAM. All you have to do
is run RedBoot in a section of RAM that you don't use for
applications.
If this functionality is needed then RedBoot needs to be
relocated.
Which I guess is what I've done.
Since the main reason for doing this is often to allow RedBoot
to be loaded via JTAG,
I usually run RedBoot from RAM because
1) On my targets, RAM is several orders of magnitude faster
than ROM, and it allows RedBoot to keep up with network
traffic better.
2) Doing things like re-formatting flash and updating RedBoot
is much simpler if your not runnning from flash.
These are precisely the reasons for ROMRAM mode - RedBoot stored in
ROM, but executing from RAM. The details of how to get it started,
in particular how to get the ROM image into RAM, etc, are [sadly]
architecture/platform dependent though.
I've been talking to our hardware guys about our next desing,
andit might not even have any any executable ROM, so RedBoot
will have to run from RAM.
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.
I've never heard of a JTAG startup type. How does it differ
from RAM startup?
RAM startups normally ignore some steps, e.g. setting up the RAM
controller, etc. A JTAG startup might allow for some of these
to happen, even in a RAM only environment. Again, very architecture
dependent.
--
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Gary Thomas | Consulting for the
MLB Associates | Embedded world
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