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Re: [avr-gcc-list] Fixed, external function "pointers"

From: Dave Hylands
Subject: Re: [avr-gcc-list] Fixed, external function "pointers"
Date: Tue, 10 Jan 2006 22:54:28 -0800

Hi Erik,

Posting to the list...

On 1/10/06, Erik Walthinsen <address@hidden> wrote:
> I've got a bootloader under development (started in C, converted to ASM
> blind, now am validating ASM piece by piece) that should fit in 512
> bytes, uses I2C for communication, and provides the application with an
> I2C register-style interface, as well as a function to write to PROGMEM
> arrays.  And of course application-code uploads when in bootloader mode.

One of the linker options is --just-symbols=filename which will import
the symbols from an objet file.

So if you import the symbols from the bootloader you can call directly
into the functions. This has potential maintenance issues (the app
will only work with a particular version of the bootloader).

Another option is to put a jump table at a known location (typically
somewhere near the beginning of the bootloader. You link the
application against the bootloader jump table entries using
--just-symbols. Now the bootloader can change quite a bit without
chaning the location of the jump table entries.

Dave Hylands
Vancouver, BC, Canada

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