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C00002 00002	      All you ever wanted to know about hardware (yawn, zzzzzz)
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      All you ever wanted to know about hardware (yawn, zzzzzz)

Some of the basic registers:
IR: instruction register; holds current instruction. Decoding of
    the actual request is done out of this register.

PC: program counter; contains the address of the instruction to
    be executed. Typical machine cycle increments this register
    (by 1); JUMPs, JUMPNILs, CALLs, and POPJs alter it differently.

AC1-n: registers to handle parameter passing.

P,Cp: stack pointers

more if needed
___________
notation as per Sec 7.2 pp165-166.

basic machine cycle:
l: c(IR)←c(c(PC))
   c(PC)←c(PC)+1   
   execute[IR]
   go l

basic control cycle suitable for recursion: 
i.e. what "execute[(CALL s fn)]" & "execute[(POPJ s)]" do.

execute[i] <=
	is_call[i] → call[stack[i];fn[i]]
	is_popj[i] → popj[stack[i]]
   ......


call[s;fn] <= 
	c(c(s)) ← c(PC)
	   c(s) ← c(s)+1
          c(PC) ← fn

popj[s]  <=			;n.b. popj has a typo in the notes.
	 c(s) ← c(s)-1
	c(PC) ← c(c(s))