.module cdtc_sqscr_configure_crtc

.z80

;; Parameters. You can set these.

; You can customize values below, to your wishes and context

_screen_first_byte_address == 0xC000
_crtc_r1_disp_width_chars == 32    ; 32 chars, 64 bytes, 256-pixel wide screen (standard is 40)
_crtc_r6_disp_height_chars == 32   ; 32 chars, 256-pixel high screen
_crtc_r9_plus_1_disp_lines_per_char_height == 8 ; standard value 8, r9 == 7

; Don't change lines below

_screen_width_in_bytes == _crtc_r1_disp_width_chars * 2
_screen_total_lines == _crtc_r6_disp_height_chars * _crtc_r9_plus_1_disp_lines_per_char_height



;; Some sanity checks

.iif gt, (_crtc_r1_disp_width_chars - 63) .mexit ; ERROR CPC only accepts up to 63 characters wide screen

.iif gt, (_crtc_r6_disp_height_chars - 32) .mexit ; ERROR This routine so far cannot handle screens with more than 256 lines.  Please comment, vote or contribue on https://github.com/cpcitor/cpc-dev-tool-chain/issues

.iif gt, (_crtc_r1_disp_width_chars * _crtc_r6_disp_height_chars - 1024) .mexit ; ERROR screen specifications too big.  CPC cannot output more that 1024 characters in MODE 1 without overscan.  This routine does not support 32k overscan screens yet.



        .globl _crtc_r1_disp_width_chars
        .globl _crtc_r6_disp_height_chars
        .globl _screen_first_byte_address
        .globl _screen_width_in_bytes

_cdtc_screen_basic__configure_crtc::
        ld bc, #0xbc01
        out (c), c
        ld bc, #0xbd00 + _crtc_r1_disp_width_chars
        out (c), c

        ;; horizontal centering
        ld bc, #0xbc02
        out (c), c
        ld bc, #0xbd00 + 46 + ((_crtc_r1_disp_width_chars-40)/2)
        out (c), c

        ld bc, #0xbc06
        out (c), c
        ld bc, #0xbd00 + _crtc_r6_disp_height_chars
        out (c), c

        ;; vertical centering
        ld bc, #0xbc07
        out (c), c
        ld bc, #0xbd00 + 30 + ((_crtc_r6_disp_height_chars-24)/2)
        out (c), c

        ld bc, #0xbc09
        out (c), c
        ld bc, #0xbd00 + (_crtc_r9_plus_1_disp_lines_per_char_height - 1)
        out (c), c

        ld bc, #0xbc09
        out (c), c
        ld bc, #0xbd00 + (_crtc_r9_plus_1_disp_lines_per_char_height - 1)
        out (c), c

        ret