From 66358574c30fd95a8bcf7e3f268dd08799274996 Mon Sep 17 00:00:00 2001
From: Alan Cox <alan@linux.intel.com>
Date: Wed, 3 Oct 2018 14:36:10 +0100
Subject: [PATCH] vdp1: do proper interrupt blocking

This fixes the odd very weird happening because the TMS9918A data pointer is
messed up by register accesses (eg interrupts mid scroll). Also fix the
timing for MSX1. We can't quite otir/inir a TMS9918A on MSX but must use
outi ; jp nz in order to run at the required access rate.
---
 Kernel/dev/vdp1.s | 56 ++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 46 insertions(+), 10 deletions(-)

diff --git a/Kernel/dev/vdp1.s b/Kernel/dev/vdp1.s
index 07d0629e..d6a2be61 100644
--- a/Kernel/dev/vdp1.s
+++ b/Kernel/dev/vdp1.s
@@ -10,6 +10,8 @@
 	    .globl cursor_off
 	    .globl cursorpos
 
+	    .globl _int_disabled
+
 	    .globl _vdpport
 
 	    .globl vdpinit
@@ -79,6 +81,9 @@ plot_char:  pop hl
 	    push bc
 	    push de
 	    push hl
+	    ld a,(_int_disabled)
+	    push af
+	    di
 plotit:
 	    ld b, #0x40			; writing
 	    call videopos
@@ -89,6 +94,11 @@ plotit2:
 	    out (c), h			; address | 0x40
 	    dec c
 	    out (c), a			; character
+popret:
+	    pop af
+	    or a
+	    ret nz
+	    ei
 	    ret
 
 ;
@@ -110,7 +120,9 @@ scrollbuf:   .ds		40
 _scroll_down:
 		.endif
 scroll_down:
-	    ret
+	    ld a,(_int_disabled)
+	    push af
+	    di
 	    ld b, #23
 	    ld de, #0x3C0	; start of bottom line
 upline:
@@ -120,7 +132,9 @@ upline:
 	    out (c), e		; our position
 	    out (c), d
 	    dec c
-	    inir		; safe on MSX2 but not MSX1? - FIXME 
+down_0:
+	    ini
+	    jp nz, down_0
 	    inc c
 	    ld hl, #0x4028	; go down one line and into write mode
 	    add hl, de		; relative to our position
@@ -129,18 +143,23 @@ upline:
 	    ld b, #0x28
 	    ld hl, #scrollbuf
 	    dec c
-	    otir		; video ptr is to the line below so keep going
+down_1:
+	    outi		; video ptr is to the line below so keep going
+	    jp nz,down_1
 	    pop bc		; recover line counter
 	    ld hl, #0xffd8
 	    add hl, de		; up 40 bytes
 	    ex de, hl		; and back into DE
 	    djnz upline
-	    ret
+	    jp popret
 
 		.if VDP_DIRECT
 _scroll_up:
 		.endif
 scroll_up:
+	    ld a,(_int_disabled)
+	    push af
+	    di
 	    ld b, #23
 	    ld de, #40		; start of second line
 downline:   push bc
@@ -149,7 +168,9 @@ downline:   push bc
 	    out (c), e
 	    out (c), d
 	    dec c
-	    inir		; MSX1 fixme ?
+up_0:
+	    ini
+	    jp nz, up_0
 	    inc c
 	    ld hl, #0x3FD8	; up 40 bytes in the low 12 bits, add 0x40
 				; for write ( we will carry one into the top
@@ -160,13 +181,15 @@ downline:   push bc
 	    dec c
 	    ld hl, #scrollbuf
 	    ld b, #0x40
-	    otir		; FIXME: is otir ok for MSX 1 ???
+up_1:
+	    outi
+	    jp nz,up_1
 	    pop bc
 	    ld hl, #40
 	    add hl, de
 	    ex de, hl
 	    djnz downline
-	    ret
+	    jp popret
 
 		.if VDP_DIRECT
 _clear_lines:
@@ -176,6 +199,9 @@ clear_lines:
 	    pop de	; E = line, D = count
 	    push de
 	    push hl
+	    ld a,(_int_disabled)
+	    push af
+	    di
 	    ld c, d
 	    ld d, #0
 	    ld b, #0x40
@@ -195,7 +221,7 @@ l1:	    out (c), a		; Inner loop clears a line, outer counts
             djnz l1
 	    dec e
 	    jr nz, l2
-	    ret
+	    jp popret
 
 		.if VDP_DIRECT
 _clear_across:
@@ -207,6 +233,9 @@ clear_across:
 	    push bc
 	    push de
 	    push hl
+	    ld a,(_int_disabled)
+	    push af
+	    di
 	    ld b, #0x40
 	    call videopos
 	    ld a, c
@@ -218,7 +247,7 @@ clear_across:
 	    dec c
 l3:	    out (c), a
             djnz l1
-	    ret
+	    jp popret
 
 ;
 ;	FIXME: should use attribute blink flag not a char
@@ -231,6 +260,9 @@ cursor_on:
 	    pop de
 	    push de
 	    push hl
+	    ld a,(_int_disabled)
+	    push af
+	    di
 	    ld (cursorpos), de
 	    ld b, #0x00			; reading
 	    call videopos
@@ -249,10 +281,14 @@ cursor_on:
 _cursor_off:
 		.endif
 cursor_off:
+	    ld a,(_int_disabled)
+	    push af
+	    di
 	    ld de, (cursorpos)
 	    ld a, (cursorpeek)
 	    ld c, a
-	    call plotit
+	    jp plotit
+
 _vtattr_notify:
 	    ret
 
-- 
2.34.1