;;********************************************************************************
;; @module ps2_keyboard 
;; @type driver
;; @details:
;;  Support for a PS2 Keyboard using the shift register of a 6522 VIA
;;  @section reading Reading a scancode/command answer
;;   Pressing a key causes 11 bits to be sent: 1 start - 8 scancode - 1 parity - 1 stop 
;;   The VIA is set up to interrupt after 8 bits have been shifted into the shift register
;;   from the external clock pulses of the keyboard (additional hardware required to 
;;   address the hardware bug of the VIA, where bit get lost when the external clock 
;;   transition happens during falling edge of PHI2). After reading the shift register,
;;   the VIAs T2 timer is set to interrupt after the last 3 bits have been shifted in,
;;   which takes about ~230ms.
;;	 T2 is used because it leaves to more versatile T1 available for something else
;; 
;;  @section processing Processing a scancode
;;	 The scancode may be processed by storing the address of a handler subroutine in
;;	 `ps2kb::scancode_handler`. This handler can load the scancode byte from `ps2kb::scancode`.
;;
;;  
;;  To use a different layout, change the enum K and the CHARS_NOMOD and CHARS_MODSHIFT
;; @warning
;;  The value with which the timer is loaded must depends on the clock frequency
;;	of the keyboard and the computer
;;  
;;********************************************************************************
.ifndef INCLUDE_PS2_KEYBOARD
INCLUDE_PS2_KEYBOARD = 1
.include "system.h65"

.scope ps2kb
Import ps2kb, init, begin_receive, scancode, status, scancode_handler
Import ps2kb, _receive_irq_shift_reg_handler, _receive_irq_timer_handler, _send_byte, _send_irq_shift_reg_handler, _send_irq_timer_handler,
Import ps2kb, send_command, send_cmd, send_data, cmd_response, response_length, FMT_CMD_FAIL

VIA = IO1
; Enough time must pass for 3 bits to be shifted in.
; TIMER_RECV = 230  ; 230 ms (@1MHz)
TIMER_RECV = 400  ; 230 ms (@1MHz)
; Enough time must pass for one bit must be shifted out (parity),
; but at most two (parity+stop).
; After that, the interrupt must have happened because the keyboard will pull data low.
; At that point, the SR needs to be set to input again
; TIMER_SEND = 230  ; 180 ms (@1MHz)
TIMER_SEND = 400  ; 180 ms (@1MHz)

PULL_REG = IO::RANH
PULL_DDR = IO::DDRA
; use RA4 to pull the clock low
PULL_MASK_CLK = %00010000

; using ff because 0 is a possible data byte (set led)
NO_DATA     = $ff   ; indicates that no data byte should be send
NO_RESPONSE = $ff   ; indicates a command did not receive a response (yet)
ACK         = $fa   ; successful transmission
RESEND      = $fe   ; unsuccessful transmission


.enum STATUS
    RECEIVE_KEYS	= %10000000     ; keyboard sends scancodes
    RECEIVE_ANSWER	= %01000000     ; keyboard replies to a command
    SEND_CMD   		= %00100000     ; host sends/sent the command byte
    SEND_DATA   	= %00010000     ; host sends/sent the data byte
    SEND_RECV   	= %00001000     ; keyboard sends additional data byte
    SEND        	= SEND_CMD | SEND_DATA | SEND_RECV ; host is sending something, only used for checking status
    NONE			= %00000000
.endenum

.enum TYPEMATIC
    REPEAT_MASK     = %00011111     ; 00000 = 30Hz, ..., 11111 = 2Hz
    DELAY250        = %00000000
    DELAY500        = %00100000
    DELAY750        = %01000000
    DELAY1000       = %01100000
.endenum
.endscope

; see https://wiki.osdev.org/PS/2_Keyboard
.macro ps2kb_CmdEcho
    lda #$ee
    ldx #ps2kb::NO_DATA
    ldy #0
    jsr ps2kb::send_command
.endmacro

.macro ps2kb_CmdSetLeds mask
    lda #$ed
    .ifnblank mask
    ldx #mask
    .endif
    ldy #0
    jsr ps2kb::send_command
.endmacro

.macro ps2kb_CmdGetScancodeSet
    lda #$f0
    ldx #0
    ldy #1
    jsr ps2kb::send_command
.endmacro

.macro ps2kb_CmdSetScancodeSet set
    .assert set = 1 .or set = 2 .or set = 3, warning, "ps2kb_CmdSetScancodeSet: invalid scancode set"
    lda #$f0
    ldx #set
    ldy #0
    jsr ps2kb::send_command
.endmacro

.macro ps2kb_CmdIdentify
    lda #$f2
    ldx #ps2kb::NO_DATA
    ldy #2
    jsr ps2kb::send_command
.endmacro

.macro ps2kb_CmdTypematicSettings settings
    lda #$f3
    ldx #settings
    ldy #0
    jsr ps2kb::send_command
.endmacro

.macro ps2kb_CmdEnable
    lda #$f4
    ldx #ps2kb::NO_DATA
    ldy #0
    jsr ps2kb::send_command
.endmacro

.macro ps2kb_CmdDisable
    lda #$f5
    ldx #ps2kb::NO_DATA
    ldy #0
    jsr ps2kb::send_command
.endmacro

.macro ps2kb_CmdSetTypematic scancode
    ldy #0
    .ifblank scancode
    lda #$f7
    ldx #ps2kb::NO_DATA
    .else
    lda #$fb
    ldx #scancode
    .endif
    jsr ps2kb::send_command
.endmacro

.macro ps2kb_CmdSetMakeRelease scancode
    ldy #0
    .ifblank scancode
    lda #$f8
    ldx #ps2kb::NO_DATA
    .else
    lda #$fc
    ldx #scancode
    .endif
    jsr ps2kb::send_command
.endmacro

.macro ps2kb_CmdSetMake scancode
    ldy #0
    .ifblank scancode
    lda #$f9
    ldx #ps2kb::NO_DATA
    .else
    lda #$fd
    ldx #scancode
    .endif
    jsr ps2kb::send_command
.endmacro

.macro ps2kb_CmdSelfTest
    lda #$ff
    ldx #ps2kb::NO_DATA
    ldy #1
    jsr ps2kb::send_command
.endmacro

.macro ps2kb_WaitFinishCmd
:
    wai
    lda ps2kb::status
    and #ps2kb::STATUS::SEND
    bne :-
.endmacro

.macro ps2kb_PrintCmdFailed
    Printf ps2kb::FMT_CMD_FAIL,ps2kb::send_cmd,ps2kb::send_data,ps2kb::cmd_response,ps2kb::cmd_response+1,ps2kb::cmd_response+2
.endmacro


.endif  ; guard