From 45f5263d58e5cf46aee77d73cc492e499e8ae025 Mon Sep 17 00:00:00 2001
From: Alan Cox <alan@linux.intel.com>
Date: Sun, 2 Sep 2018 21:58:21 +0100
Subject: [PATCH] nascom: commit the vt work in progress ready for 0.2

---
 Kernel/platform-nascom/nascom-vt.s | 162 +++++++++++++++++++++++++++++
 1 file changed, 162 insertions(+)
 create mode 100644 Kernel/platform-nascom/nascom-vt.s

diff --git a/Kernel/platform-nascom/nascom-vt.s b/Kernel/platform-nascom/nascom-vt.s
new file mode 100644
index 00000000..f2ca50c2
--- /dev/null
+++ b/Kernel/platform-nascom/nascom-vt.s
@@ -0,0 +1,162 @@
+;
+;	The Nascom has a fairly simple default video console except
+;	that each line has margins of space that are used for other
+;	stuff
+;
+		.module nascom-vt
+
+
+		.globl _cursor_off
+		.globl _cursor_disable
+		.globl _cursor_on
+		.globl _plot_char
+		.globl _clear_lines
+		.globl _clear_across
+		.globl _vtattr_notify
+		.globl _scroll_up
+		.globl _scroll_down
+
+
+		.area _CODE
+;
+;	Required to preserve BC
+;
+addr:		
+		ld a,e		; get Y
+		dec a		; weird line wrapping
+		and #15
+		add a,a
+		add a,a
+		add a,a
+		add a,a		; x16: as far as we can 8bit add
+		ld l,a
+		ld h,#0
+		ld e,d
+		ld d,h		; DE is now 00xx where xx is the X value
+		add hl,hl	; x 32
+		add hl,hl	; x 64
+		ld de,#0xF800
+		add hl,de
+		ret
+
+_cursor_off:
+		ld hl,(cpos)
+		bit 7,h		; all valid cpos values are > 0x8000
+		ret z
+		ld a,(csave)
+		ld (hl),a
+		xor a
+		ld (cpos+1),a
+_cursor_disable:
+		ret
+
+_cursor_on:
+		pop hl
+		pop de
+		push de
+		push hl
+		call addr
+		ld a,(hl)
+		ld (hl),#'_;
+		ld (csave),a
+		ld (cpos),hl
+		ret
+
+_plot_char:
+		pop hl
+		pop de
+		pop bc
+		push bc
+		push de
+		push hl
+		ld (hl),c
+		ret
+
+;
+;	The weird layout means we can't do a single ldir
+;
+_clear_lines:
+		pop hl
+		pop de
+		push de		; E = Y D = count
+		push hl
+		ld c,d
+		ld d,#0
+wipenext:
+		push de
+		call addr
+		xor a
+wipeline:
+		ld b,#48
+wiper:		ld (hl),#' '
+		inc hl
+		djnz wiper
+		pop de
+		inc e
+		dec d
+		jr nz, wipenext
+		ret
+
+_clear_across:
+		pop hl
+		pop de		; E = y D = x
+		pop bc		; C = count
+		push bc
+		push de
+		push hl
+		call addr
+		ld a,#' '
+		ld b,c
+clear2:		ld (hl),a
+		inc hl
+		djnz clear2
+_vtattr_notify:
+		ret
+
+_scroll_up:
+		; Do the special case first
+		ld hl,#0xF80A
+		ld de,#0xFBCA
+		ld bc,#48
+		ldir
+		ld de,#0xF80A
+		ld hl,#0xF84A
+		; BC is always 0 here
+		ld a,#15
+nextup:
+		ld c,#48
+		ldir
+		ld c,#16
+		add hl,bc
+		ex de,hl
+		add hl,bc
+		ex de,hl
+		pop bc
+		dec a
+		jr nz,nextup
+		ret
+
+_scroll_down:
+		ld hl,#0xFB79
+		ld de,#0xFBB9
+		ld a,#15
+nextdown:
+		ld bc,#48
+		lddr
+		ld bc,#0xFFF0		; - 16
+		add hl,bc
+		ex de,hl
+		add hl,bc
+		ex de,hl
+		dec a
+		jr nz, nextdown
+		; Top line special case
+		ld hl,#0xFBC0
+		ld de,#0xF800
+		ld bc,#48
+		ldir
+		ret
+
+		.area _DATA
+csave:		.byte 0
+cpos:		.word 0
-- 
2.34.1