SEC \ Set xLinear = -xLiftDragSc / 256 LDA #0 \ SBC xLiftDragScHi \ starting with the low bytes STA xLinearLo LDA #0 \ And then the high bytes SBC xLiftDragScTop STA xLinearHi SEC \ Set yLinear = (yFlapsLiftSc - yLiftDragSc) / 256 LDA yFlapsLiftScHi \ SBC yLiftDragScHi \ starting with the low bytes STA yLinearLo LDA yFlapsLiftScTop \ And then the high bytes SBC yLiftDragScTop STA yLinearHi LDA zVelocityPHi \ Set A to the high byte of the forward airspeed from \ the perspective of the plane BMI turn3 \ If it is negative, jump down to turn3 to set A = 0 and \ skip the following checks, as we only retract the \ flaps if we are going to fast in a forward direction PHA \ Store A on the stack so we can retrieve it after the \ following call to RetractFlapsIfFast JSR RetractFlapsIfFast \ Retract the flaps if we are going too fast PLA \ Retrieve the value of A from the stack CMP #48 \ If zVelocityPHi < 48, jump to turn4 BCC turn4 LDA #&EA \ Set A = &EA and jump to turn10 to set zLinearHi to BNE turn10 \ &EA and return from the subroutine (this BNE is \ effectively a JMP as A is never zero) .turn3 LDA #0 \ We jump here if the value of zVelocityPHi in A is \ negative, in which case we set A = 0, so we now have: \ \ A = max(0, zVelocityPHi) .turn4 LDX engineStatus \ If engineStatus is zero, then the engine is not BEQ turn8 \ running, so jump to turn8 to set the forward force \ from the engine to zero STA H \ Set X = max(0, zVelocityPHi) STA G \ Set G = max(0, zVelocityPHi) LDA zVelocityPLo \ Set A to the low byte of the forward airspeed LDX #3 \ Set X as a shift counter in the following loop, so we \ shift right by 4 places .turn5 LSR G \ Set (G A) = (G A) >> 1 ROR A DEX \ Decrement the shift counter BPL turn5 \ Loop back until we have shifted right by X + 1 places, \ so: \ \ (G A) = (G A) >> 4 \ = max(0, zVelocityP) / 16 STA W \ Set (G W) = (G A) \ = max(0, zVelocityP) / 16 LDY thrustHi \ Set Y to the high byte of the current thrust STY R \ Set (R A) = (thrustHi thrustLo) LDA thrustLo \ = thrust LDX L \ Fetch the current value of onGround BEQ turn7 \ If onGround is zero then we are not on the ground, so \ jump to turn7 CPY #4 \ If thrustHi < 4, jump to turn6 to skip the following BCC turn6 \ two instructions ASL A \ Set (R A) = (R A) << 1 ROL R \ \ so we double the value of (R A) if the thrust is >= \ (4 0), i.e. >= 1024 .turn6 LDY H \ If max(0, zVelocityPHi) >= 4, jump to turn7 to skip CPY #4 \ the following BCS turn7 CPY #1 \ If max(0, zVelocityPHi) < 1, jump to turn7 to skip BCC turn7 \ the following ASL A \ Set (R A) = (R A) << 1 ROL R \ \ so we double the value of (R A) again if zVelocityPHi \ is 2 or 3, which means zVelocity is in the range (2 0) \ to (3 255), or 512 to 1023 \ By now we have set (R A) to the thrust, scaled up as \ follows: \ \ * Doubled if thrust >= 1024 \ \ * Doubled if zVelocity is in the range 512 to 1023 \ \ Let's call this thrustScaled .turn7 SEC \ Set (Y X) = (R A) - (G W) SBC W \ = thrustScaled - (max(0, zVelocityP) / 16) TAX \ \ starting with the low bytes LDA R \ And then the high bytes SBC G TAY BPL turn9 \ If Y is positive, skip to turn9, otherwise keep going \ to set (Y X) = 0, so this means: \ \ (Y X) = max(0, thrustScaled \ - (max(0, zVelocityP) / 16)) .turn8 LDY #0 \ Set (Y X) = 0 LDX #0 .turn9 JSR ScaleByAltitude \ Set (Y X V) = (Y X) * ~yPlaneHi \ \ so (Y X) = (Y X) * ~yPlaneHi / 256 \ = max(0, thrustScaled \ - (max(0, zVelocityP) / 16)) \ * ~yPlaneHi / 256 \ \ or (Y X) = 0 if the engine is off TXA \ Set zLinear = (Y X) - zLiftDragSc / 256 SEC \ SBC zLiftDragScHi \ starting with the low bytes STA zLinearLo TYA \ And then the high bytes, so now we have the following SBC zLiftDragScTop \ when the engine is on: \ \ zLinear = max(0, thrustScaled \ - (max(0, zVelocityP) / 16)) \ * ~yPlaneHi / 256 \ - zLiftDragSc / 256 .turn10 STA zLinearHi \ Store the high byte of the result in zLinearHi RTS \ Return from the subroutineName: ApplyTurnAndThrust (Part 2 of 2) [Show more] Type: Subroutine Category: Flight model Summary: Calculate the (xLinear, yLinear, zLinear) vectorContext: See this subroutine in context in the source code References: No direct references to this subroutine in this source file
This part of the routine calculates the following. If zVelocityPHi >= 48 (so forward speed >= 500 mph), we calculate: [ xLinear ] [ 0 ] [ xLiftDragSc ] [ yLinear ] = [ yFlapsLiftSc ] - [ yLiftDragSc ] [ zLinear ] [ 0 ] [ (&EA zLinearLo) ] If zVelocityPHi < 48 (so forward speed < 500 mph), we calculate: [ xLinear ] [ 0 ] [ xLiftDragSc ] [ 0 ] [ yLinear ] = [ yFlapsLiftSc ] - [ yLiftDragSc ] + [ 0 ] [ zLinear ] [ 0 ] [ zLiftDragSc ] [ zEngine ] where zEngine is 0 if the engine is off, or the following if the engine is on: zEngine = max(0, thrustScaled - (max(0, zVelocityP) / 16)) * airDensity / 512 and: airDensity = ~yPlaneHi * 2 and thrustScaled is the thrust in (thrustHi thrustLo), but: * Doubled if thrust >= 1024 * Doubled if zVelocity is in the range 512 to 1023 It also calls the RetractFlapsIfFast routine to retract the flaps if we are going too fast.
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Subroutine RetractFlapsIfFast (category: Flight model)
Retract the flaps if we are going faster than 150 mph
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Subroutine ScaleByAltitude (category: Flight model)
Multiply the high byte of the plane's altitude by a 16-bit number
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Variable engineStatus in workspace Main variable workspace
Engine status
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Variable thrustHi in workspace Main variable workspace
Thrust (high byte)
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Variable thrustLo in workspace Main variable workspace
Thrust (low byte)
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Label turn10 is local to this routine
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Label turn3 is local to this routine
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Label turn4 is local to this routine
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Label turn5 is local to this routine
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Label turn6 is local to this routine
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Label turn7 is local to this routine
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Label turn8 is local to this routine
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Label turn9 is local to this routine
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Variable xLiftDragScHi in workspace Main variable workspace
Scaled linear force due to lift in the x-axis (high byte)
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Variable xLiftDragScTop in workspace Main variable workspace
Scaled linear force due to lift in the x-axis (top byte)
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Variable xLinearHi (category: 3D geometry)
High byte of point 252 (x-coordinate)
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Variable xLinearLo in workspace Main variable workspace
Low byte of point 252 (x-coordinate)
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Variable yFlapsLiftScHi in workspace Main variable workspace
Scaled linear force in the y-axis due to lift from the flaps (high byte)
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Variable yFlapsLiftScTop in workspace Main variable workspace
Scaled linear force in the y-axis due to lift from the flaps (top byte)
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Variable yLiftDragScHi in workspace Main variable workspace
Scaled linear force due to side forces in the y-axis (high byte)
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Variable yLiftDragScTop in workspace Main variable workspace
Scaled linear force due to side forces in the y-axis (top byte)
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Variable yLinearHi in workspace Main variable workspace
High byte of point 252 (y-coordinate)
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Variable yLinearLo in workspace Main variable workspace
Low byte of point 252 (y-coordinate)
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Variable zLiftDragScHi in workspace Main variable workspace
Scaled linear force due to drag in the z-axis (high byte)
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Variable zLiftDragScTop in workspace Main variable workspace
Scaled linear force due to drag in the z-axis (top byte)
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Variable zLinearLo in workspace Main variable workspace
Low byte of point 252 (z-coordinate)
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Variable zVelocityPHi in workspace Main variable workspace
Plane velocity along the z-axis from the perspective of the pilot (high byte)
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Variable zVelocityPLo in workspace Main variable workspace
Plane velocity along the a-axis from the perspective of the pilot (low byte)