What is the scope of the review of a Miranda claim?

4. Discussion--As we stated in People v. Boyer (1989) 48 Cal.3d 247, 263, 256 Cal.Rptr. 96, 768 P.2d 610, reviewing a similar claimed Miranda violation, "The scope of our review of constitutional claims of this nature is well established. We must accept the trial court's resolution of disputed facts and inferences, and its evaluations of credibility, if they are substantially supported. [Citations.] However, we must independently determine from the undisputed facts, and those properly found by the trial court, whether the challenged statement was illegally obtained. [Citation.]"