 E16 clock by clock pipeline contents during control flow changes.

 Fetching       IR contents     Decode      Control flow change
 --------       -----------     -------     ------------------------------
  I0  I1        ?   ?           ?
                                    ?
  I2  I3        I0  I1          ?
                                    I0      >>>>> interrupt pending <<<<<
  I4  I5        I2  I3          I1          irq: flush IR, load RSTn into CR
                nop nop             RSTn    rst:  push PC, flush IR, P=Q0
  Q0  Q1        nop nop         nop               |
                                    nop     ISR call/ret overhead = 8 clocks
  RET Q3        Q0  Q1          nop               |
                                    Q0            |
  Q4  Q5        RET Q3          Q1                |
                                    RET     ret:  pop PC (I4) flush IR
  I4  I5        nop nop         Q3                note: Q3 should be NOP
                                    nop
  I6  I7        I4  I5          nop
                                    I4
  JMP I9        I6  I7          I5
                                    I6
  I10 I11       JMP I9          I7
                                    JMP     jump: flush IR
  J0  J1        nop nop         I9                note: I9 should be a NOP
                                    nop
  J2  J3        J0  J1          nop
                                    J0
  J4  @{        J2  J3          J1
                                    J2
  }@  J7        J4  @{          J3
                                    J4
  --  --        }@  J7          @{          mem cycle: set address bus
                                    }@      latch data, flush IR
  J8  J9        nop nop         J7
                                    nop
  J10 J11       J8  J9          nop
                                    J8
 CALL J13       J10 J11         J9
                                    J10
  J14 J15      CALL J13         J11
                                    CALL    call: push PC (J14) flush IR
  K0  K1        nop nop         J13               |
                                    nop           |
  RET K3        K0  K1          nop               |
                                    K0            |
  K4  K5        RET K3          K1                |
                                    RET     ret:  pop PC (J14) flush IR
  L0  L1        nop nop         K3                note: K3 should be a NOP
                                    nop
 SKIP L3        L0  L1          nop
                                    L0
  L4  L5        L2  L3          L1
                                    SKIP    skip: flush IR
  L6  L7        nop nop         L3                execute L3 but skip L4L5
                                    nop
  L8  L9        L6  L7          nop
                                    L6

