Intel sez: Synchronous Flash and XIP is the future -- thoughts?
nico at cam.org
Mon Dec 16 12:21:50 EST 2002
On Mon, 16 Dec 2002, David Woodhouse wrote:
> wd at denx.de said:
> > Running the kernel XIP is not so insane. It can help to reduce boot
> > time. We still more than 3 seconds from power-on to application
> > start, which is not so bad, but still too much in some cases;
> > avoiding the memcpy() of some 2 MB of data is kind of attractive
> > then...
> That's true, although even if you have the kernel on a separate flash chip
> to which you don't ever write, it does cost you later because you then run
> from flash which is slower than RAM. I wonder if we could copy the kernel
> from flash to RAM at runtime and fix up the page tables as we go, to get the
> best of both worlds?
On ARM this has no value since the kernel takes up at most 1 or 2 page table
entries (1MB section descriptors that is).
Fortunately on ARM the kernel seems to be sane with .text and .rodata
actually being read-only.
/me who incidentally just finished hacking a XIP kernel and filesystem patch
on ARM for a customer named Intel...
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