Re: New CPM/DPRAM allocator

[Nick Garnett <nickg@ecoscentric.com>]

John Dallaway <jld@ecoscentric.com> writes:

> A few of questions:
> 
> 1) Does this incompatibilty affect _all_ targets which run both RedBoot and 
> eCos?

Just PowerPC QUICC targets, like the MBX, Adder or Viper, for example.

> 2) Could the new allocator implementation be modified in any way to preserve 
> compatibility?

Possibly. But I'll defer to Gary on this one.

> 3) To what extent might the new allocator perturb eCos functionality other 
> than by a stepwise "it will work or it will be completely broken".

It shouldn't affect anything else. Failure modes are hard to specify
since they depend on the contents of what is currently an
uninitialized location in RAM. Different instances of RedBoot might
have different values there.

We might even be able to add a test to the DPRAM code to detect an old
RedBoot and generate an error message before proceeding.

> 4) Is a further break in compatibility possible as potential issues with the 
> new allocator are ironed out?

Unlikely. The code is only a handful of lines. 

> 
> We need to determine how to manage the switch over to the new CPM/DPRAM 
> allocator smoothly for everyone. From my perspective, it is certainly 
> unfortunate that this innovation has arrived between 2.0 beta and 2.0 
> final. Were it not for the break in compatibility, I would vote against 
> incorporating this change for 2.0 final since the change will (to a certain 
> extent) invalidate beta testing by the net community. However, it would 
> also be undesirable for 2.0 final RedBoot to be incompatible with anonCVS 
> eCos from day 1. Users are likely to want to stick with a release version 
> of the firmware while experimenting with eCos from anonCVS.
> 

It only affects a handful of boards: MBX, VIPER, ADDER, TS1000. QUICC2
targets like the tS6 and VADS are not affected, and non-QUICC MPC8xx
targets like the CMA28x and FADS boards are not affected.

-- 
Nick Garnett                    eCos Kernel Architect
http://www.ecoscentric.com/     The eCos and RedBoot experts