Dashboard: cntr

       Name: cntr                                                    [Show more]
       Type: Subroutine
   Category: Dashboard
    Summary: Apply damping to the pitch or roll dashboard indicator
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * Main flight loop (Part 2 of 16) calls cntr


 This routine does a similar job to the routine of the same name in the BBC
 Master version of Elite, but the code is significantly different.


 Arguments:

   A                    The amount to dampen by

   X                    The value to dampen


 Returns:

   X                    The dampened value


.cntr1

 LDX #128               ; Set X = 128 to return so we don't dampen past the
                        ; middle of the indicator

.cntr2

 RTS                    ; Return from the subroutine

.cntr

 STA T                  ; Store the argument A in T

 LDA auto               ; If the docking computer is currently activated, jump
 BNE cntr3              ; to cntr3 to skip the following as we always want to
                        ; enable damping for the docking computer

 LDA DAMP               ; If DAMP is zero, then damping is disabled, so jump to
 BEQ cntr2              ; cntr2 to return from the subroutine

.cntr3

 TXA                    ; If X >= 128, then it's in the right-hand side of the
 BMI cntr4              ; dashboard slider, so jump to cntr4 to decrement it by
                        ; T to move it closer to the centre

                        ; If we get here then the current value in X is in the
                        ; left-hand side of the dashboard slider, so now we
                        ; increment it by T to move it closer to the centre

 CLC                    ; Set A = A + T
 ADC T

 BMI cntr1              ; If the addition pushed A to 128 or higher, jump to
                        ; cntr1 to return a value of X = 128, so we don't dampen
                        ; past the middle of the indicator

 TAX                    ; Set X to the newly dampened value

 RTS                    ; Return from the subroutine

.cntr4

 SEC                    ; Set A = A - T
 SBC T

 BPL cntr1              ; If the subtraction reduced A to 127 or lower, jump to
                        ; cntr1 to return a value of X = 128, so we don't dampen
                        ; past the middle of the indicator

 TAX                    ; Set X to the newly dampened value

 RTS                    ; Return from the subroutine