Messages in this thread | | | Subject | Re: FFS2 and MTDs (flash) | Date | Mon, 5 Jul 1999 21:35:09 +0200 (MEST) | From | (Rogier Wolff) |
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David Woodhouse wrote: > > Think of CFI-compliant flash mapped into the host's address space. Why cache > it in RAM when you can just point a page table at the original?
One of the things is that the ROMs and flash devices that you're talking about are usually only 8 or 16 bits wide. That means that you get worse access times than 32- or 64-bit wide RAM. If you just copy the page from the device into main memory the only thing that YOU'll notice is that it is a whole lot faster than a disk. Once you start executing code out of it, the first thing you'll notice is that it's slower than RAM.... ;-)
XIP is useful though for very cramped machines. Say one with 4M RAM and 16M flash. You might even want the kernel to stay put in the flash. Possibly have the choice of running the one important application (e.g. the mp3 decompressor in the empeg-car) get copied over to RAM before execution....
Roger.
-- ** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2137555 ** *-- BitWizard writes Linux device drivers for any device you may have! --* ------ Microsoft SELLS you Windows, Linux GIVES you the whole house ------
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