msx2: Make the cursor work

I was clearly not awake pasting the initial cursor code together.

This gives us a correct text rendering, except for the mysterious double
copy which presumably is a VDP set up error of some kind.

diff --git a/Kernel/platform-msx2/vdp.s b/Kernel/platform-msx2/vdp.s
index f17645d..7bb0c5b 100644 (file)
--- a/Kernel/platform-msx2/vdp.s
+++ b/Kernel/platform-msx2/vdp.s
@@ -123,6 +123,7 @@ plotit:
            ld b, #0x40                 ; writing
            call _videopos
            ld a, c
+plotit2:
            ld bc, (_vdpport)
            out (c), l                  ; address
            out (c), h                  ; address | 0x40
@@ -256,12 +257,23 @@ _cursor_on:
            push de
            push hl
            ld (cursorpos), de
-           ld c, #'_'
-            call plotit
-           ret
+           ld b, #0x00                 ; reading
+           call _videopos
+           ld a, c
+           ld bc, (_vdpport)
+           out (c), l                  ; address
+           out (c), h                  ; address
+           dec c
+           in a, (c)                   ; character
+           ld (cursorpeek), a          ; save it away
+           set 6, h                    ; make it a write command
+           ld a, #'_'                  ; write the cursor
+           jp plotit2
+
 _cursor_off:
            ld de, (cursorpos)
-           ld c, #' '
+           ld a, (cursorpeek)
+           ld c, a
            call plotit
            ret
 ;
@@ -269,3 +281,4 @@ _cursor_off:
 ;
            .area _DATA
 cursorpos:  .dw 0
+cursorpeek: .db 0