In People v. Hayton (1979) 95 Cal.App.3d 413, a claim of pretrial delay was analyzed as follows: "Issues cognizable on an appeal following a guilty plea are limited to issues based on 'reasonable constitutional, jurisdictional, or other grounds going to the legality of the proceedings' resulting in the plea. (Pen. Code, 1237.5.) The reason for this rule is that 'a plea of guilty admits all matters essential to the conviction.' ( People v. DeVaughn (1977) 18 Cal.3d 889, 895.) Obtaining a certificate of probable cause does not make cognizable those issues which have been waived by a plea of guilty. ( People v. Kaanehe (1977) 19 Cal.3d 1, 9.) Therefore, section 1237.5 of the Penal Code does not expand the grounds upon which an appeal may be taken after a guilty plea, but 'merely establishes a procedure for screening out frivolous claims among these issues which have not been waived.' ( People v. Kaanehe, supra, at p. 9.) . . . Thus, although the constitutional right to speedy trial is fundamental , we conclude that a defendant may not raise the issue on appeal after he has pleaded guilty." (Id., at pp. 416, 418.) In explicating its conclusion, the Hayton court reasoned that: "The essence of a defendant's speedy trial or due process claim in the usual case is that the passage of time has frustrated his ability to establish his innocence. The resolution of a speedy trial or due process issue necessitates a careful assessment of the particular facts of a case in order that the question of prejudice may be determined. para. Where the defendant pleads guilty, there are no facts to be assessed. And since a plea of guilty admits every element of the offense charged, there is no innocence to be established." (Id., at p. 419.)