I am curious if Microcontrolers are effected by the vulnerabilities of Meltdown and Spectre. These devices are not specifically CPUs, and do not run Operating Systems per-say. I'm not really sure I understand the whole speculative execution attack, but I would like to know if this can effect things like microcontrolers, which are used to drive many IOT devices.
In general, no, for several reasons.
First, Meltdown is an issue with how Intel chose to handle invalid memory accesses during speculative execution. A couple of ARM designs are vulnerable to a variant of Meltdown, but other than that, it's Intel-only.
Second, Meltdown and Spectre both require that the CPU use a technique called "speculative execution". This is a great performance boost, but it comes at the cost of a bigger, more expensive, and more power-hungry chip. Microcontrollers are small, cheap, low-power chips -- exactly the opposite of what would use speculative execution.
Third, Meltdown and Spectre are about getting around memory protection. The typical microcontroller only runs a single program, so applying memory protection is a waste of time and effort -- any memory a program could read using Meltdown or Spectre, the program could read just by looking at it.