Who here have experience of running software written for 80C52 on LPC1778? Is it likely to work right away or will it crash? I have an existing design with existing software that I'm thinking of upgrading.
"Is it likely to work right away"
It is unlikely in the extreme that it will even build straight away!
However, If it is carefully designed for portability; ie, target dependencies (including toolset dependencies) are minimised and carefully isolated into easily identified areas, then the job of porting should be straightforward.
But, if that were the case, would you have had to ask the question...?