dphar...@telus.net wrote:
Since bootloaders need to establish communications in order to function, it
would seem useful to be able to use some of this functionality by the bootloaded
application code. In particular, this is in relation to CAN, where the boot-up
code will need to establish a node-id, and be able to communicate serial number
information to a central node.
Obviously, access to the serial number, and links to the CAN driver routines,
would be useful in the applications code, and would save duplication.
How would one go about producing a header or library file that would let you
link references to the routines in the bootloader for use in the application?
Well, I started down the path of creating a general solution, but
haven't done sufficient QA to release it to the world yet... perhaps you
would like to alpha test?
I added a small, upward compatible tweak to the linker scripts to insert
an "entry jump" section right after the interrupt vectors. Then a
simple set of conditional assembler macros is used to build two
different .o files from a single, trivial .S file that defines the
shared functions. One .o is the actual trampoline jumps that go in the
bootloader. The other .o is external definitions for the application to
link against. As long as you do not change the order of the entry jumps
and only add, and do not delete functions, the bootloader and
application can be independently updated.
The linker script changes are upward compatible, in that if there is no
entry jump section the script yields the same result as the production
scripts, so it can become your regular linker script.
I have gotten as far as trying a tiny handful of non-functional examples
and examining the disassembled binary. It looks OK, but has not yet
been smoke tested. Let me know if you would like to try it out and I'll
bundle up the code for you. I'm not going to get around to more testing
until I finish my current (PIC... yuch) contract.
The idea is not original to me. I started with some code that Joerg
sent to me that was sent to him by somebody else. And Data General, I
believe, used the "entry jump" concept to call system functions and
switch to protected mode in 1960's and 70's era mini-computers.
-dave
Thanks,
David
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