.include "keyboard.h65"
.include "string.h65"
.include "lcd.h65"
Export kb,init,irq_shift_reg_handler,irq_timer_handler,scancode,key_read
Export kb, CHARS_NOMOD, CHARS_MODSHIFT
ExportZp kb,status

.zeropage
status: 
.bss
key_read: .res 2
scancode:  .res 1

.code
;;********************************************************************************
;; @function Initialize the PS2 keyboard
;; @modifies: A
;;********************************************************************************
.proc init
    ; - use the shift register interrupts to read the first 8 bits
    ;   set shift register to shift in under external clock on CB1
    ; - configure timer for timing the read of the last 3 bits
    ;   timer 2 one shot mode is sufficient, leaves T1 available
    lda #(IO::ACR::SR_SIN_PHIE | IO::ACR::T2_IRQ_LOAD)
    tsb kb::KB_IO + IO::ACR
    ; the 3 last bits take about 230us, at @1MHz => wait 230 cycles and then the shift register
    ; (this could be shorter since the it takes a few cycles after the interrupt)
    lda #230
    sta kb::KB_IO + IO::T2CL
    stz key_read
    stz key_read+1
    stz scancode
    stz status

    ; enable SR interrupts
    lda #(IO::IRQ::IRQ | IO::IRQ::SR)
    sta kb::KB_IO + IO::IER
    ; load SR to reset
    lda kb::KB_IO + IO::SR
    rts
.endproc


;;********************************************************************************
;; @function Read the first 8 bits an
;; @modifies: A
;; @details
;;  - read shift register
;;  - disable shift register interrupts
;;  - reset shift register
;;  - enable timer 2 interrupts
;;  - start timer 2
;;  IO::SR has to be read before the next bit is shifted in, which happens ~75us after the irq
;;  at 1MHz, handling this interrupt takes about 50us (without any additional debug code),
;;  so it should work
;;********************************************************************************
.proc irq_shift_reg_handler
    lda kb::KB_IO + IO::SR
    sta key_read
    stz kb::KB_IO + IO::SR

    ; disable SR interrupts
    lda #IO::IRQ::SR
    sta kb::KB_IO + IO::IER
    ; enable timer interrupts
    lda #(IO::IRQ::IRQ | IO::IRQ::T2)
    sta kb::KB_IO + IO::IER
    ; start timer, low order count already in latch after init
    lda #0
    sta kb::KB_IO + IO::T2CH
    rts
.endproc


;;********************************************************************************
;; @function Read the last 3 bits after after timer 2 is up
;; @modifies: A
;; @details
;;  - read shift register
;;  - disable timer 2 interrupts
;;  - enable shift register interrupts
;;  - reset shift register
;;********************************************************************************
.proc irq_timer_handler
    lda kb::KB_IO + IO::SR
    sta key_read + 1

    lda kb::KB_IO + IO::T2CL  ; clear interrupt flag

    ; disable timer interrupts
    lda #(IO::IRQ::T2)
    sta kb::KB_IO + IO::IER

    ; reset SR
    ; disabling shifting in acr seems necessary to reset - otherwise
    ; it continues counting and interrupts after the first 5 bits of the next keypress
    lda #(IO::ACR::SR_SIN_PHIE | IO::ACR::T2_IRQ_LOAD)
    trb kb::KB_IO + IO::ACR
    tsb kb::KB_IO + IO::ACR
    stz kb::KB_IO + IO::SR
    ; enable shift register interrupts
    lda #(IO::IRQ::IRQ | IO::IRQ::SR)
    sta kb::KB_IO + IO::IER

    lda key_read+1
    ror
    ror
    ror
    lda key_read  ; not affecting carry
    rol           ; rotate carry into byte, rotate startbit into carry
    Reverse A
    sta scancode

    rts
.endproc

.rodata
.align 256
CHARS_NOMOD:
        .byte "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00^\x00"
        .byte "\x00\x00\x00\x00\x00q1\x00\x00\x00ysaw2\x00"
        .byte "\x00cxde43\x00\x00 vftr5\x00"
        .byte "\x00nbhgz6\x00\x00\x00mju78\x00"
        .byte "\x00,kio09\x00\x00.-l\xEFp\xE2\x00"
        .byte "\x00\x00\xE1\x00\xF5`\x00\x00\x00\x00\x00\x00\x00#\x00\x00"
        .byte "\x00<\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
        .byte "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"

.align 256
CHARS_MODSHIFT:
        .byte "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xDF\x00"
        .byte "\x00\x00\x00\x00\x00Q!\x00\x00\x00YSAW\"\x00"
        .byte "\x00CXDE$\xED\x00\x00 VFTR%\x00"
        .byte "\x00NBHGZ&\x00\x00\x00MJU/(\x00"
        .byte "\x00;KIO=)\x00\x00:_L\xEFP\xE2\x00"
        .byte "\x00\x00\xE1\x00\xF5`\x00\x00\x00\x00\x00\x00\x00'\x00\x00"
        .byte "\x00>\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
        .byte "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"