AUTO_INC_NONE = $00
AUTO_INC_1 = $01
AUTO_INC_2 = $02
AUTO_INC_4 = $03
AUTO_INC_8 = $04
AUTO_INC_16 = $05
AUTO_INC_32 = $06
AUTO_INC_64 = $07
AUTO_INC_128 = $08
AUTO_INC_256 = $09
AUTO_INC_512 = $0A
AUTO_INC_40 = $0B
AUTO_INC_80 = $0C
AUTO_INC_160 = $0D
AUTO_INC_320 = $0E
AUTO_INC_640 = $0F

DISABLED = 0
ENABLED = 1

VERA_L_BPP1 = %00000000
VERA_L_BPP2 = %00000001
VERA_L_BPP4 = %00000010
VERA_L_BPP8 = %00000011

VERA_L_BITMAP = %00000100
VERA_L_T256C = %00001000

VERA_L_32W = %00000000
VERA_L_64W = %00010000
VERA_L_128W = %00100000
VERA_L_256W = %00110000

VERA_L_32H = %00000000
VERA_L_64H = %01000000
VERA_L_128H = %10000000
VERA_L_256H = %11000000

VERA_TILESIZE8x8 = %00000000
VERA_TILESIZE16x8 = %00000001
VERA_TILESIZE8x16 = %00000010
VERA_TILESIZE16x16 = %00000011

; The base address of the VERA chip
VERA_BASE = $00DF00

; Offsets (relative to VERA_BASE) for each VERA register

VERA_ADDRx_L = VERA_BASE + 00
VERA_ADDRx_M = VERA_BASE + 01
VERA_ADDRx_H = VERA_BASE + 02

; Accssible with ADDRSEL == 0
VERA_ADDR0_L = VERA_BASE + 00
VERA_ADDR0_M = VERA_BASE + 01
VERA_ADDR0_H = VERA_BASE + 02

; Accssible with ADDRSEL == 1
VERA_ADDR1_L = VERA_BASE + 00
VERA_ADDR1_M = VERA_BASE + 01
VERA_ADDR1_H = VERA_BASE + 02

VERA_DATA0 = VERA_BASE + $03
VERA_DATA1 = VERA_BASE + $04

VERA_CTRL = VERA_BASE + $05
VERA_IEN = VERA_BASE + $06
VERA_ISR = VERA_BASE + $06
VERA_IRQLINE_L = VERA_BASE + $07
VERA_SCANLINE_L = VERA_BASE + $08

; Accssible with DCSEL == 0
VERA_DC_VIDEO = VERA_BASE + $09
VERA_DC_HSCALE = VERA_BASE + $0A
VERA_DC_VSCALE = VERA_BASE + $0B
VERA_DC_BORDER = VERA_BASE + $0C

; Accssible with DCSEL == 1
VERA_DC_HSTART = VERA_BASE + $09
VERA_DC_HSTOP = VERA_BASE + $0A
VERA_DC_VSTART = VERA_BASE + $0B
VERA_DC_VSTOP = VERA_BASE + $0C

; Layer 0
VERA_L0_CONFIG = VERA_BASE + $0D
VERA_L0_MAPBASE = VERA_BASE + $0E
VERA_L0_TILEBASE = VERA_BASE + $0F
VERA_L0_HSCROLL_L = VERA_BASE + $10
VERA_L0_HSCROLL_H = VERA_BASE + $11
VERA_L0_VSCROLL_L = VERA_BASE + $12
VERA_L0_VSCROLL_H = VERA_BASE + $13

; Layer 1
VERA_L1_CONFIG = VERA_BASE + $14
VERA_L1_MAPBASE = VERA_BASE + $15
VERA_L1_TILEBASE = VERA_BASE + $16
VERA_L1_HSCROLL_L = VERA_BASE + $17
VERA_L1_HSCROLL_H = VERA_BASE + $18
VERA_L1_VSCROLL_L = VERA_BASE + $19
VERA_L1_VSCROLL_H = VERA_BASE + $1A

; Audio
VERA_AUDIO_CTRL = VERA_BASE + $1B
VERA_AUDIO_RATE = VERA_BASE + $1C
VERA_AUDIO_DATA = VERA_BASE + $1D

; SPI (Unused in prototype four!)
VERA_SPI_DATA = VERA_BASE + $1E
VERA_SPI_CTRL = VERA_BASE + $1F

; VRAM layout
TEXT_CONSOLE_TILES = $0800
TEXT_CONSOLE0_VRAM = $1800
VERA_PSG_BASE = $1F9C0
VERA_PALETTE_BASE = $1FA00
VERA_SPRITE_ATTR_BASE = $1FC00

; vera_address_select - selects the active VERA address register
; Selecting 0 means that the address registers control the address
; accessed by VERA_DATA0, while selecting 1 means controlling the
; address for VERA_DATA1.
vera_address_select .macro value
    pha

    lda #(\value & %00000001)
    tsb VERA_CTRL

    pla
.endmacro

; vera_address_set  - sets the address registers to the passed in value
vera_address_set .macro addr
    pha

    lda #>\addr
    sta VERA_ADDRx_L
    
    lda #<\addr
    sta VERA_ADDRx_M
    
    lda #`\addr
    sta VERA_ADDRx_H
    
    pla
.endmacro

; vera_address_incr - set the VERA address auto-increment.
vera_address_incr .macro increment
    pha

    ; Clear the top four bits of ADDRx_H (increment value and decrement bit)
    lda #%11111000
    trb VERA_ADDRx_H

    ; Set the new value
    lda #\increment << 4
    tsb VERA_ADDRx_H

    pla
.endmacro

; vera_address_decr - set the VERA address auto-decrement.
vera_address_decr .macro decrement
    pha

    ; Clear the top five bits of ADDRx_H
    lda #%11110000
    trb VERA_ADDRx_H

    ; Set the new value (and the decrement bit)
    lda #(\increment << 4) | %00001000
    tsb VERA_ADDRx_H

    pla
.endmacro

; Copies up to 64KB of two-byte data to VERA memory, beginning at
; the provided address in VERA's address space.
;
; Arguments:
;   target:     The address in VERA memory at which the
;               copied data will begin
;   source:     The address in CPU memory at which the data
;               to be copied begins
;   length:     The number of bytes to copy to VERA memory. Must
;               be a multiple of 2.
vera_write .macro target, source, length
    .save_registers

    ; Set up the address/data VERA registers for 16-bit copying.

    .vera_address_select 0
    .vera_address_set \{target}
    .vera_address_incr AUTO_INC_2
    .vera_address_select 1
    .vera_address_set \{target} + 1
    .vera_address_incr AUTO_INC_2

    .long_a
    
    ldx #0
copy_loop:
    lda \{source},X
    sta VERA_DATA0
    inx
    inx
    cpx #\{length}
    beq copy_loop

    .restore_registers
.endmacro

; Copies up to 64KB of two-byte data to CPU memory from VERA
; memory.
;
; Arguments:
;   target:     The address in CPU memory at which the
;               copied data will begin
;   source:     The address in VERA memory at which the data
;               to be copied begins
;   length:     The number of bytes to copy from VERA memory. Must
;               be a multiple of 2.
vera_read .macro target, source, length
    .save_registers

    ; Set up the address/data VERA registers for 16-bit copying.

    .vera_address_select 0
    .vera_address_set \{source}
    .vera_address_incr AUTO_INC_2
    .vera_address_select 1
    .vera_address_set \{source} + 1
    .vera_address_incr AUTO_INC_2

    .long_a
    
    ldx #0
copy_loop:
    lda VERA_DATA0
    sta \{target},X
    inx
    inx
    cpx #\{length}
    beq copy_loop

    .restore_registers
.endmacro