Keyboard: ReadJoystick

       Name: ReadJoystick                                            [Show more]
       Type: Subroutine
   Category: Keyboard
    Summary: Read the joystick axes and fire button and update the aileron,
             elevator and fire key values accordingly
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * UpdateFlightModel (Part 1 of 4) calls ReadJoystick


.ReadJoystick

 LDA row29_char20_4     \ If the screen byte at row 29, block 20, pixel row 4 is
 BEQ rjoy1              \ zero (i.e. black) then the joystick is not enabled, so
                        \ jump to rjoy1 to return from the subroutine

 LDX #1                 \ Set aileronPosition to the value from ADC channel 1,
 JSR ReadADCChannel     \ the joystick's x-position, inverted and clipped to the
 STA aileronPosition    \ range -118 to +116

 LDX #2                 \ Set elevatorPosition to the value from ADC channel 2,
 JSR ReadADCChannel     \ the joystick's y-position, inverted and clipped to the
 STA elevatorPosition   \ range -118 to +116

 LDX #0                 \ Call OSBYTE with A = 128 and X = 0 to read the status
 LDA #128               \ of the joystick's fire button into X
 JSR OSBYTE

 TXA                    \ If bit 0 of X is zero, the fire button is not being
 AND #1                 \ pressed, so jump to rjoy1
 BEQ rjoy1

 LDA #8                 \ The fire button is being pressed, so update the key
 STA keyLoggerLo+5      \ logger at keyLoggerLo+5, which corresponds to the
                        \ flaps and fire keys. We set the value to 8, the value
                        \ from keyTable2Lo for the fire button

.rjoy1

 RTS                    \ Return from the subroutine

 EQUB &36