🚀 go-pugleaf

I've been merrily working my way through the book "Operating System
Design, The XINU Approach" by Douglas Comer (copyright 1984) until
this exercise - haven't been able to answer all the exercises but felt
that with {some, enough} perspiration they could be done - until I
tried exercise 10 at the end of chapter 5 :

"Procedure chprio contains a serious design flaw.  Find it, describe its
consequences, and repair it.".

That's the only reference to chprio in the index.
Is the design flaw that chprio tests only for the PRFREE state ...
if that's not it, what is the flaw?  Is there a later
edition of the book where this is discussed?

Secondly, has anyone ported xinu over to the Zilog Z280 cpu?

Thanks for any and all help,
dciem!lfergus!larry (Larry Moore)