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#1 2006-03-16 13:47:25

chris
Member
Germany
Registered: 2006-03-06
Last visit: 2006-08-25
Posts: 13

Size of firmware image

Hi,
how large can a firmware image? Are there restrictions on the compressed or the uncompressed size?

Chris

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#2 2006-03-16 20:53:44

HH
Developer
Registered: 2006-02-15
Last visit: 2007-03-12
Posts: 103

Re: Size of firmware image

The practical limit is what can fit into the space on the Flash device, and that is the compressed kernel image.  There are 4 things on the flash.  (1) bootloader, size ~32K.  (2) Non-volatile variables saved on the flash, size varies according to device type but is generally less than 100K (my dual-WAN router uses 96K but other devices can and do use a lot less). (3) webpages, size 64K (obsolete but every OEM firmware still uses it, possibly because the first 4 chars identify the device). (4) Compressed kernel, size = what's left over after 1-3 are accounted for.

Roughly, if you have a 2 MB flash chip there's about 1.8 MB available for the compressed kernel and if you have a 4 MB flash chip there's about 3.8 available.

The RAM size limit on the uncompressed kernel is, I believe, 6 MB.

Last edited by HH (2006-03-16 20:55:14)

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