6502-OS/system/lcd.s65

.include "system/lcd.h65"

.ifndef lcd::LCD_IO
.fatal "lcd::LCD_IO is not defined: set it to the base address of the IO chip of the LCD"
.endif

Export lcd,init,clear,print,print_char,set_position,set_custom_char
Export lcd,_cmd,_wait_nbusy,_write_ram,_read_ram,_set_dd_ram_addr_from_charcount
Export lcd,_charcount
; RAM VARIABLES
.bss
_charcount:  .res 1

; @TODO when clockspeeds are more than 1MHz, _cmd, _write_ram and _read_ram might need to be adjusted
.code
;;********************************************************************************
;; @function Initialize the lcd module
;; @details call before doing anything else
;; @modifies A
;;********************************************************************************
.proc init
    ; init IO
    lda #$ff                        ; RB 0-7 output
    sta lcd::LCD_IO+IO::DDRB

    lda lcd::LCD_IO+IO::DDRA
    ora #(lcd::RS | lcd::RW | lcd::E)
    sta lcd::LCD_IO+IO::DDRA

    ; init lcd
    lda #lcd::CMD::FUNCTION_SET  
    jsr _cmd
    lda #lcd::CMD::DISPLAY_ON
    jsr _cmd
    lda #lcd::CMD::CLEAR
    jsr _cmd
    lda #lcd::CMD::ENTRY_MODE
    jsr _cmd

    stz _charcount
    rts
.endproc


;;********************************************************************************
;; @function Set the cursor to a position
;; @param A: cursor position: `(lcd::LINEX + offset)`, where offset € [$0, $f]
;; @details:
;;  If the position is too large, it will be set to char 4 in line 2
;; @returns A: the cursor position
;;********************************************************************************
.proc set_position
    pha
    cmp #$60
    bge @invalid
    cmp #$50
    bge @line4
    cmp #$40
    bge @line2
    cmp #$20
    bge @invalid
    cmp #$10
    bge @line3
    bra @set
; @line1:  ; starts at $00, _charcount at $00
@line2:  ; starts at $40, _charcount at $10
    sbc #$30  ; carry is already set
    bra @set
@line3:  ; starts at $10, _charcount at $20
    add #$10
    bra @set
@line4:  ; starts at $50, _charcount at $30
    sbc #$20
@set:
    sta _charcount
    pla
    pha
    ora #lcd::CMD::SET_ADDRESS
    jsr _cmd
    ; and #(<~lcd::CMD::SET_ADDRESS)  ; return original argument
    pla
    rts
@invalid:
    pla  ; otherwise stack corruption
    lda #$13
    sta _charcount
    lda #(lcd::CMD::SET_ADDRESS | (lcd::LINE2 + 3))
    jsr _cmd
    lda #(lcd::LINE2 + 3)
    rts
.endproc

;********************************************************************************
; PRINTING TO LCD
;********************************************************************************

;;********************************************************************************
;; @function Clear the display
;; @see lcd_print
;; @modifies A
;;********************************************************************************
.proc clear
    stz _charcount
    lda #lcd::CMD::CLEAR
    jsr _cmd
    rts
.endproc

;;********************************************************************************
;; @function Print a null-terminated string
;; @param ARG0-1 Address of the string to print
;; @modifies: A,Y
;; @returns Y: Length of the string
;;********************************************************************************
.proc print
    ldy #$00
@lcd_print_loop:
    lda (ARG0),y
    beq @lcd_print_end
    jsr print_char
    iny
    bra @lcd_print_loop
@lcd_print_end:
    rts
.endproc


;;********************************************************************************
;; @function Print a single character
;; @param A: Character to print
;;********************************************************************************
.proc print_char
    pha
    jsr _write_ram
    inc _charcount
    jsr _break_line
    pla ; put char back in a
.endproc


;;********************************************************************************
;; @function Write a custom character to the lcds CharacterGenerator (CG) RAM
;; @param A: The ASCII code: 0-7
;; @param ARG0-1: Start address of the 8 bytes describing the character
;; @returns: C: 0 => success, 1 => invalid argument
;; @modifies: A,Y
;;********************************************************************************
.proc set_custom_char
    cmp #8
    bcs @rts  ; >= 8
    rol  ; address is bytes 3-5
    rol 
    rol
    ora #lcd::CMD::SET_CG_ADDRESS
    jsr lcd::_cmd
    ldy #0
@loop:
    lda (ARG0),y
    jsr lcd::_write_ram
    iny
    cpy #8
    bne @loop
    clc
@rts:
    rts
.endproc


;;********************************************************************************
;; Internal LCD Commands
;;********************************************************************************
;; @function Wait until the lcd is no longer busy
;; @details
;;  Reads from the address until the busy flag is no longer set.
;;  After reading, the VIA will be set to output mode again
;;********************************************************************************
.proc _wait_nbusy
    pha
    stz lcd::LCD_IO + IO::DDRB           ; set IO1-IO + IO::RB to input
    lda lcd::LCD_IO + IO::RA
    and #<~lcd::RA_MASK
    ora #lcd::RW
    sta lcd::LCD_IO + IO::RA

@lcd_wait_nbusy_loop:   ; read the busy flag
    ; set E low, then high
    lda lcd::LCD_IO + IO::RA
    and #<~lcd::E
    sta lcd::LCD_IO + IO::RA
    ora #lcd::E
    sta lcd::LCD_IO + IO::RA
    
    lda lcd::LCD_IO + IO::RB
    bmi @lcd_wait_nbusy_loop   ; msb set
    
    lda lcd::LCD_IO + IO::RA
    and #<~lcd::RA_MASK
    sta lcd::LCD_IO + IO::RA
    lda #%11111111   ; set IO1-IO + IO::RB to output
    sta lcd::LCD_IO + IO::DDRB
    pla
    rts
.endproc


;;********************************************************************************
;; @function Send a @ref lcd::CMD "command" to the lcd
;; @param A: command
;; @modifies A
;;********************************************************************************
.proc _cmd
    jsr _wait_nbusy

    sta lcd::LCD_IO + IO::RB

    ; while preserve bits 0-4: unset E, set RS
    ; unset E, RW and  RS
    lda lcd::LCD_IO + IO::RA
    and #(<~lcd::RA_MASK)
    sta lcd::LCD_IO + IO::RA
    ; set E
    ora #lcd::E
    sta lcd::LCD_IO + IO::RA
    ; unset E
    eor #lcd::E
    sta lcd::LCD_IO + IO::RA
    rts
.endproc


;;********************************************************************************
;; @function Write a byte to the lcd
;; @details
;;  Set the CG or DD address first
;; @param A: data
;; @modifies A
;;********************************************************************************
.proc _write_ram
    jsr _wait_nbusy
    sta lcd::LCD_IO + IO::RB
    ; while preserve bits 0-4: unset E and RW, set RS
    lda lcd::LCD_IO + IO::RA
    and #(<~lcd::RA_MASK)
    ora #lcd::RS
    sta lcd::LCD_IO + IO::RA
    ; set E
    ora #lcd::E
    sta lcd::LCD_IO + IO::RA
    ; unsert E
    eor #lcd::E
    sta lcd::LCD_IO + IO::RA
    rts
.endproc


;;********************************************************************************
;; @function Read a byte from the lcd
;; @details
;;  Set the CG or DD address first
;; @returns A: byte
;;********************************************************************************
.proc _read_ram
    jsr _wait_nbusy
    ; set IO1-IO + IO::RB to input
    stz lcd::LCD_IO + IO::DDRB  
    ; while preserve bits 0-4: unset E, set RW and RS
    lda lcd::LCD_IO + IO::RA
    and #(<~lcd::RA_MASK)
    ora #(lcd::RW | lcd::RS)
    sta lcd::LCD_IO + IO::RA
    ; set E
    ora #lcd::E
    sta lcd::LCD_IO + IO::RA
    ; load the byte 
    lda lcd::LCD_IO + IO::RB
    pha
    ; unset E
    lda lcd::LCD_IO + IO::RA
    eor #lcd::E
    sta lcd::LCD_IO + IO::RA
    ; set IO1-IO + IO::RB to output
    lda #$ff
    sta lcd::LCD_IO + IO::DDRB
    pla
    rts
.endproc


;;********************************************************************************
;; @function Set the LCD DD-RAM Address from the character count
;; @details
;;  Sets the DD-RAM Address so that a line break occurs after 16 characters
;;  If _charcount is more than $40, the position will be set to _charcount % $40
;;********************************************************************************
.proc _set_dd_ram_addr_from_charcount
    cmp #$40  ; set to line1 when full
    bcs @wrap_to_line1 ; a € [$40, $ff]
    cmp #$10
    bcc @line1  ; a € [$00, $0f]
    cmp #$20
    bcc @line2  ; a € [$10, $1f]
    cmp #$30
    bcc @line3  ; a € [$20, $2f]
    ; bra @line4; a € [$30, $3f]
@line4:
    clc
    adc #$20        ; _charcount $30-$3f -> $50 - $5f
    bra @set_address
@wrap_to_line1:
    and #%00111111
    ; now every _charcount is mapped between 0 and $3f
    bra @set_address
@line2:
    adc #$30        ; _charcount $10-$1f -> $40 - $4f
    bra @set_address
@line3:
    sec
    sbc #$10        ; _charcount $20-$2f -> $10 - $1f
    bra @set_address
@line1:             ; _charcount $00-$1f -> $00 - $0f - nothing to do
@set_address:
    ora #lcd::CMD::SET_ADDRESS
    jsr _cmd
    rts
.endproc

;;********************************************************************************
;; @function Set the LCD DD-RAM Address to te next line if the end of the line was reached
;; @details
;;  If the cursor is past the end of a line, the DD-RAM Address is set to the next line.
;;  If _charcount is more than $40, the position will be set to line 1.
;;  This function is intended to be used with to set the correct address when
;;  auto-shift is enabled
;;********************************************************************************
.proc _break_line
    ; check if checks are necessary
    lda _charcount
    beq @line1
    bit #%10001111  ; ($10 | $20 | $30 | $40) = %01110000
    beq @check
    rts
@check:
    ; checks necessary
    cmp #$10
    beq @line2
    cmp #$20
    beq @line3
    cmp #$30
    beq @line4
    cmp #$40  ; set to line1 when full
    bge @line1 
    rts
@line1:
    stz _charcount
    lda #(lcd::CMD::SET_ADDRESS | lcd::LINE1)
    jsr _cmd
    rts
@line2:
    lda #(lcd::CMD::SET_ADDRESS | lcd::LINE2)
    jsr _cmd
    rts
@line3:
    lda #(lcd::CMD::SET_ADDRESS | lcd::LINE3)
    jsr _cmd
    rts
@line4:
    lda #(lcd::CMD::SET_ADDRESS | lcd::LINE4)
    jsr _cmd
    rts
.endproc