NMI injection

Hi All, Can someone clarify me what is “NMI injection” means? Does it helps when system is frozen? If so how to do this for Intel Atom processor machines? I configured my system to respond for SysRq key press, but I see when system is frozen then SysRq key press has no effect. I’ve read that when kernel is locked up it won’t respond for SysRq key press actions. What is the definition for “kernel locked up” means? And how to solve this? -- Thanks, Sekhar