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Diffstat (limited to 'scroll/include/joypad.s')
| -rw-r--r-- | scroll/include/joypad.s | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/scroll/include/joypad.s b/scroll/include/joypad.s new file mode 100644 index 0000000..8711c28 --- /dev/null +++ b/scroll/include/joypad.s @@ -0,0 +1,63 @@ +.segment "CODE" + +;;; +;; Joypad controller code. The following memory addresses are reserved: $21-$23. +;; +;; Memory address $21 is used for internal purposes, whereas $22 and $23 contain +;; the bitmask of the buttons that are pressed from each controller. +;;; + +.scope Joypad + ;; Button masks. + BUTTON_A = 1 << 7 + BUTTON_B = 1 << 6 + BUTTON_SELECT = 1 << 5 + BUTTON_START = 1 << 4 + BUTTON_UP = 1 << 3 + BUTTON_DOWN = 1 << 2 + BUTTON_LEFT = 1 << 1 + BUTTON_RIGHT = 1 << 0 + + ;; Port addresses for controllers. + JOYPAD1 = $4016 + JOYPAD2 = $4017 + + ;; We keep all the information from controller from mainly two variables: + ;; m_buttons1 and m_buttons2; containing respectively the buttons pressed + ;; for this frame for both controllers. The m_inv_buttons ($21) is an + ;; internal variable and should not be used for anything outside of this + ;; usage. + m_inv_buttons = $21 + m_buttons1 = $22 + m_buttons2 = $23 + + ;; READ_CONTROLLER reads the input from the controller mapped into the given + ;; port, and saves the state into the given `buttons` address. + ;; Implementation taken from NESHacker's example of smb3-like movement. + .macro READ_CONTROLLER port, buttons + lda m_inv_buttons + tay + lda #1 + sta port + sta m_inv_buttons + lsr + sta port + : + lda port + lsr + rol m_inv_buttons + bcc :- + tya + eor m_inv_buttons + and m_inv_buttons + sta buttons + .endmacro + + ;; read sets the values for m_buttons1 and m_buttons2 as read from both + ;; controllers. + .proc read + READ_CONTROLLER JOYPAD1, m_buttons1 + READ_CONTROLLER JOYPAD2, m_buttons2 + rts + .endproc +.endscope |