From: Grant Edwards <grante@visi.com>
To: Gary Thomas <gthomas@cygnus.co.uk>
Cc: ecos <ecos-discuss@sourceware.cygnus.com>
Subject: Re: [ECOS] ARM vectors.S question
Date: Wed, 27 Oct 1999 07:01:00 -0000 [thread overview]
Message-ID: <19991027090116.B14874@visi.com> (raw)
In-Reply-To: <XFMail.991027062141.gthomas@cygnus.co.uk>
On Wed, Oct 27, 1999 at 06:21:41AM -0600, Gary Thomas wrote:
> > Perhaps my prejudices from doing 15 years of embedded systems are
> > showing, but I don't see how any system could be laid out this way.
> > Perhaps I don't understand how the power-up reset works in the CPU?
>
> No, we would never assume that RAM survives a reset :-)
>
> Most hardware that has RAM at 0x0 and the ROM somewhere else has shadow
> magic that makes the ROM appear at 0x0, either for a fixed number of cycles
> after reset or until a control latch is reset.
Ah yes, about 20 years ago I had an S-100 bus Z-80 bus system that did
the shadow rom for X cycles after reset trick. I had forgotten about that.
> Firstly, you should consider working from the public CVS repository. This
> has the latest stuff in it, including much work that lets items such as
> this be specified in platform specific files, not directly in "vectors.S".
OK, I'll take a look at the CVS tree -- having to modify what were
supposed to be platform-independant files made me think that I was
headed in the wrong direction. Are there semi-stable CVS snapshots,
or is a guy pretty much rolling the dice when using sources from the
CVS tree?
> Are you using the CVS version, or some other source release?
I'm using the 1.2.1 official release.
> I'll try and provide help/guidance with whatever changes you need.
> Note that there are other places than "vectors.S" that expect low memory
> to be writeable so vectors can be updated. Unless you can take the
> "remap" route, there will be other considerations.
Thanks. That's a very useful tip. I should be able to go either way:
remapping ROM/RAM in startup code or having ROM vectors go through
RAM. Initially I was thinking of sticking with the ROM vectors, but
it sounds like remapping might be a better idea.
> > I must say that the ARM load/store instructions are about the coolest
> > I've seen since the PDP-11.
>
> I shudder to think what you've been working with...
Mostly the usual crop of embedded architectures (8086, 8051, 68HC11,
68332) and the TI TMS32C320 DSP for a while [it was wierd having
sizeof (everyting) == 1].
--
Grant Edwards
grante@visi.com
next prev parent reply other threads:[~1999-10-27 7:01 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-10-26 13:44 Grant Edwards
1999-10-26 15:05 ` Gary Thomas
1999-10-26 18:42 ` Grant Edwards
1999-10-27 4:00 ` Hugo Tyson
1999-10-27 5:14 ` Gary Thomas
1999-10-27 7:01 ` Grant Edwards [this message]
1999-10-27 7:09 ` Gary Thomas
1999-10-27 1:04 ` Dan Hovang
2013-10-12 14:54 [ECOS] ARM Vectors.S Question Michael Jones
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