PowerPlay Report - 'Simulation Zero' versus 'Default' Toggle Rate

All,

I've generated a .vcd file in the Modelsim environment with:

vcd file test.vcd

vcd add -r tb/dut/*

As far as I can tell all of the signals in my design are recorded into that file. When I use the .vcd file with Quartus PowerPlay, the section 'Confidence Metric Details' of the power report breaks out as follows:

+------------------------------------------------------------------------------------------------------------------------------------------------------+
; Confidence Metric Details                                                                                                                            ;
+----------------------------------------------------------------------------------------+---------------+-------------+---------------+---------------+
; Data Source                                                                            ; Total         ; Pin         ; Registered    ; Combinational ;
+----------------------------------------------------------------------------------------+---------------+-------------+---------------+---------------+
; Simulation (from file)                                                                 ;               ;             ;               ;               ;
;     -- Simulation time nodes in unknown state                                          ; 0.1%          ;             ;               ;               ;
;     -- Number of signals with Toggle Rate from Simulation                              ; 10092 (10.9%) ; 520 (85.8%) ; 9037 (24.7%)  ; 535 (1.0%)    ;
;     -- Number of signals with Zero toggle rate, from Simulation                        ; 7421 (8.0%)   ; 9 (1.5%)    ; 7297 (20.0%)  ; 115 (0.2%)    ;
;     -- Number of signals with Static Probability from Simulation                       ; 10092 (10.9%) ; 520 (85.8%) ; 9037 (24.7%)  ; 535 (1.0%)    ;
;                                                                                        ;               ;             ;               ;               ;
; Node, entity or clock assignment                                                       ;               ;             ;               ;               ;
;     -- Number of signals with Toggle Rate from Node, entity or clock assignment        ; 11 (0.0%)     ; 0 (0.0%)    ; 0 (0.0%)      ; 11 (0.0%)     ;
;     -- Number of signals with Static Probability from Node, entity or clock assignment ; 11 (0.0%)     ; 0 (0.0%)    ; 0 (0.0%)      ; 11 (0.0%)     ;
;                                                                                        ;               ;             ;               ;               ;
; Vectorless estimation                                                                  ;               ;             ;               ;               ;
;     -- Number of signals with Toggle Rate from Vectorless estimation                   ; 0 (0.0%)      ; 0 (0.0%)    ; 0 (0.0%)      ; 0 (0.0%)      ;
;     -- Number of signals with Static Probability from Vectorless estimation            ; 0 (0.0%)      ; 0 (0.0%)    ; 0 (0.0%)      ; 0 (0.0%)      ;
;                                                                                        ;               ;             ;               ;               ;
; Default assignment                                                                     ;               ;             ;               ;               ;
;     -- Number of signals with Toggle Rate from Default assignment                      ; 80564 (86.7%) ; 0 (0.0%)    ; 27503 (75.3%) ; 53061 (95.2%) ;
;     -- Number of signals with Static Probability from Default assignment               ; 82797 (89.1%) ; 86 (14.2%)  ; 27503 (75.3%) ; 55208 (99.0%) ;
;                                                                                        ;               ;             ;               ;               ;
; Assumed 0                                                                              ;               ;             ;               ;               ;
;     -- Number of signals with Toggle Rate assumed 0                                    ; 2233 (2.4%)   ; 86 (14.2%)  ; 0 (0.0%)      ; 2147 (3.9%)   ;
+----------------------------------------------------------------------------------------+---------------+-------------+---------------+---------------+

Question:

Why is the use of 'Default assignment' non-zero. What causes a signal to be assigned my default toggle rate VERSUS determining from simulation that there is 'Zero toggle rate'. Is my .vcd file at fault?

Thanks,

Cam