On the Proton compiler forum Tim posted this on a thread about ModBus:

"Yes I know instant interrupts I was the one who came up with and implemented the idea in the first place. I also know the limitations, you have to save every single system reg on entry and restore it on exiting. Even Protons managed interrupts which work on a similar system is 10x better as it only saves the regs you used.

But the beauty of Proton is that if you are careful you can write your code with out using a single system reg

It a nice idea to boost the response of the Interrupts, native in PBP or DT-INTS.

And by the way, we have been waiting long for a nice surprise from Melabs. Anything cooking?