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On Thu, 16 Jul 2009, tom wrote: > Gordon Henderson wrote: >> On Thu, 16 Jul 2009, Paul Hirst wrote: >> >>> On Wed, 2009-07-15 at 11:06 +0100, Rob Beard wrote: >>> >>>> As far as I know (after watching the demo video) they use an >>>> uncompressed kernel with only drivers which the hardware requires and >>>> use DMA access to transfer the stuff into memory, I gather too that the >>>> hardware is pretty limited due to it being designed for in-car use. >>>> >>> I would have thought a gzip compressed kernel would make the most sense. >>> They are bzip2 compressed by default aren't they? Which is pretty slow >>> to decompress compared to gzip. >>> >>> Can you still do 'make zImage' rather than 'make bzImage'? I haven't >>> compiled a kernel in a number of years now. The last one must have been >>> the last Gentoo system I built. >>> >> >> I'll give it a try soon, but the current kernels now support LZMA >> compression which is supposed to be much faster to uncompress. >> > Just wondering if this is a legacy feature or whether loading and > decompressing is faster than just loading an already decompressed > kernel? Obviously system dependent but intrigued to see any figures... If you can uncompress and write to RAM at the same speed as you can read from storage media, then having a compressed kernel should always be faster as you're reading less in from the chosen media (Flash, hard-drive, cd-rom, usb key, etc.) It will all boil down to the efficiency of the uncompression. Another factor to consider is cost - especially if you're making 1000's of units - I have a friend who works for a certian "data robot" storage device company and they want as little flash on-board as they can get away with - because it costs more when building millions of them, so you might find that you have no choice but to compress. When I first put together the process I use today for my "embedded" devices, 32MB Flash IDE drives were expensive. These days 256MB ones are cheaper, so that's what I use, but I still compress because it's easier... Actually, in the grand scheme of things, for my own units, having a boot time of a minute or so is more than acceptable. Snom VoIP phones which also run Linux take about a minute to startup themselves anyway. Gordon -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/linux_adm/list-faq.html