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Controllers: UpdateJoystick

[NES version, Bank 7]

Name: UpdateJoystick [Show more] Type: Subroutine Category: Controllers Summary: Update the values of JSTX and JSTY with the values from the controller Deep dive: Bolting NES controllers onto the key logger
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * NMI calls UpdateJoystick
.UpdateJoystick LDA QQ11a ; If the old view in QQ11a is not the space view, then BNE SetControllerPast ; jump to SetControllerPast to set the controller ; history variables to the values from four VBlanks ago ; and return from the subroutien using a tail call LDX JSTX ; Set X to the current roll rate in JSTX LDA #8 ; Set joystickDelta = 8, to use as the amount by which STA joystickDelta ; we change the roll rate by for each button press LDY numberOfPilots ; Set Y to numberOfPilots, which will be 0 if only one ; pilot is configured, or 1 if two pilots are configured ; ; As the rest of this routine updates the joystick based ; on the values in controller1Right + Y etc., this means ; that when the game is configured for two pilots, the ; routine updates the joystick variables based on the ; buttons being pressed on controller 2 ; ; In other words, when two pilots are configured, ; controller 2 steers the ship while controller 1 looks ; after the weaponry BNE joys1 ; If numberOfPilots = 1 then the game is configured for ; two pilots, so skip the following so that holding down ; the B button on controller 1 doesn't stop controller 2 ; from updating the flight controls LDA controller1B ; If the B button is being pressed on controller 1 then BMI joys10 ; the arrow should be used to control the icon bar and ; ship speed, rather than the ship's steering, so jump ; to joys10 to return from the subroutine .joys1 LDA controller1Right,Y ; If the right button is not being pressed, jump to BPL joys2 ; joys2 to skip the following instruction JSR DecreaseJoystick ; The right button is being held down, so decrease the ; current roll rate in X by joystickDelta .joys2 LDA controller1Left,Y ; If the left button is not being pressed, jump to joys3 BPL joys3 ; to skip the following instruction JSR IncreaseJoystick ; The left button is being held down, so increase the ; current roll rate in X by joystickDelta .joys3 STX JSTX ; Store the updated roll rate in JSTX TYA ; If Y is non-zero then the game is configured for two BNE joys4 ; pilots, so jump to joys4... though as this is the very ; next line, this has no effect .joys4 LDA #4 ; Set joystickDelta = 4, to use as the amount by which STA joystickDelta ; we change the pitch rate by for each button press LDX JSTY ; Set X to the current pitch rate in JSTY LDA JSTGY ; If JSTGY is $FF then the game is configured to reverse BMI joys8 ; the controller y-axis, so jump to joys8 to change the ; pitch value in the opposite direction LDA controller1Down,Y ; If the down button is not being pressed, jump to joys5 BPL joys5 ; to skip the following instruction JSR DecreaseJoystick ; The down button is being held down, so decrease the ; current pitch rate in X by joystickDelta .joys5 LDA controller1Up,Y ; If the up button is not being pressed, jump to joys7 BPL joys7 ; to skip the following instruction .joys6 JSR IncreaseJoystick ; The up button is being held down, so increase the ; current pitch rate in X by joystickDelta .joys7 STX JSTY ; Store the updated pitch rate in JSTY RTS ; Return from the subroutine .joys8 LDA controller1Up,Y ; If the up button is not being pressed, jump to joys9 BPL joys9 ; to skip the following instruction JSR DecreaseJoystick ; The up button is being held down, so decrease the ; current pitch rate in X by joystickDelta (as the game ; is configured to reverse the joystick Y channel) .joys9 LDA controller1Down,Y ; If the down button is being pressed, jump to joys6 to BMI joys6 ; increase the current pitch rate in X by joystickDelta ; (as the game is configured to reverse the joystick Y ; channel) STX JSTY ; Store the updated pitch rate in JSTY RTS ; Return from the subroutine .joys10 RTS ; Return from the subroutine