Re: [Fud] Constrained Firmware update challenge

Michael Richardson <mcr+ietf@sandelman.ca> Mon, 17 April 2017 15:26 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Carsten Bormann <cabo@tzi.org>
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Date: Mon, 17 Apr 2017 11:26:21 -0400
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Subject: Re: [Fud] Constrained Firmware update challenge
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Carsten Bormann <cabo@tzi.org> wrote:
    > How do you update that bootloader (which now contains the majority of
    > the code on the device, by the way)?

I think that it may be possible to significantly simply that code path
such that it does not have so much code.  Updates may be impossible
(burnt into ROM), or it might just be a special part of the flash that
is seperate from the main code.

Things I would expect to leave out would include:
       - L2 neighbour cache and L3 routing
       - fragment creation (just re-assembly)
       - neighbor discovery
       - RPL
       - DTLS and/or OSCOAP setup.
       - authorization: public key handling, certs if used, ACE tokens, DH
       - interrupts (everything polled I/O)

This is part of my postulate, and perhaps you will reasonably disagree with
the assumption that this can be done.  I believe that the code would be
seperate from the normal code.   Done wrong it could contain the majority
of the code, but done well, I think it would be perhaps 20%.

Effectively, we no longer double buffer the entire system, just the totally
minimal code required to load new code.  It could alternatively be that the
bootloader code is used as a kind of "BIOS" via subroutines.

--
Michael Richardson <mcr+IETF@sandelman.ca>ca>, Sandelman Software Works
 -= IPv6 IoT consulting =-