The PRU is a proprietary TI architecture that is totally different from the Cortex M3. The PRU is a low-level deterministic real-time 32-bit microcontroller, while the Cortex M3 is a "real processor" with interrupts, memory management and so forth. The instruction sets and architectures have nothing in common.

Maybe you're thinking of the Cortex M3 that's on the chip for power management?

Different chip/vendor but Freescale's i.mx7 is an AMP design with a Cortex A7 + an M4 presumably for the realtime bits. I had the same thought w/r/t development on the PRU.

http://www.nxp.com/products/microcontrollers-and-processors/...

Ah, you're right, it does look like that's the case. It's a shame it's not something better supported (like a cortex variant).

I think newer chips have the option for CortexM companion. This goes bit beyond my skillset, but I think the point of proprietary PRU ISA was that they could ensure super specific and regular instruction timings, every instruction being executed in single cycle with no pipelining or other stuff that can make real-time programming more tricky. That is something that afaik you simply can't do with Cortex M cores.

Cortex-R series is the equivalent to the PRU.

'R' for realtime.... in-order scheduing, highly optimised for determinism over performance.

(Having said that.... 'M' series is pretty good too really).