msx2: various platform side and vdp fixes

With these and the small core fixes to follow we blow up for reasons I don't
yet understand in the uput() call in create_init. Presumably some kind of
mapping setup bug. With that commented we hit the boot device request, at
which point we have no keyboard.

Display is still wonky. Guess it wants an MSXpert to figure out whats wrong
with the 80x25 setup

Kernel/platform-msx2/crt0.s

@@ -39,7 +39,14 @@
 ;
 ; Execution begins with us correctly mapped and at 0x0x100
 ;
+; We assume here that the kernel packs below 48K for now we've got a few
+; KBytes free but revisit as needed
+;
 start:		di
+	        ld a, #4		; 0 holds 8K of stuff we might want
+                out (0xff), a		; if we go the OS route, so use 4
+					; plus "0" is magic so this saves
+					; shifting them all by one.
 		; Debug port
 		ld a, #0x23
 	        out (0x2e), a

Kernel/platform-msx2/devtty.c

@@ -161,7 +161,7 @@ static void keydecode(void)
 
 #endif
 
-void platform_interrupt(void)
+void tty_interrupt(void)
 {
 #if 0
 	uint8_t a = irqmap;

Kernel/platform-msx2/main.c

@@ -30,12 +30,18 @@ void pagemap_init(void)
     int i = msxmaps - 1;
     /* Add all the RAM, except 0,1,2,3 which is the kernel data/bss, add 0
        last to become the common for init */
-    while (i > 3)
+    while (i > 4)
         pagemap_add(i--);
     /* Init will pick this up correctly as its common */
-    pagemap_add(0);
+    pagemap_add(4);
 }
 
 void map_init(void)
 {
 }
+
+
+void platform_interrupt(void)
+{
+	timer_interrupt();
+}

Kernel/platform-msx2/msx2.s

@@ -237,10 +237,8 @@ _program_vectors:
 ;
 map_process_always:
 	    push hl
-	    push af
 	    ld hl, #U_DATA__U_PAGE
 	    call map_process_2
-	    pop af
 	    pop hl
 	    ret
 ;
@@ -251,23 +249,18 @@ map_process:
 	    or l
 	    jr nz, map_process_2
 ;
-;	Map in the kernel below the current common, all registers preserved
-;	This maps 0-3 but I guess we should save the map from the boot
-;	somehow and use that?
+;	Map in the kernel below the current common, go via the helper
+;	so our cached copy is correct.
 ;
 map_kernel:
-	    push af
-	    ld a, #3
-	    out (0xFC), a
-	    dec a
-	    out (0xFD), a
-	    dec a
-	    out (0xFE), a
-	    ; and 0xFF is managed by task switches
-	    pop af
-            ret
+	    push hl
+	    ld hl, #map_kernel_data
+	    call map_process_2
+	    pop hl
+	    ret
 map_process_2:
 	    push de
+	    push af
 	    ld de, #map_table	; Write only so cache in RAM
 	    ld a, (hl)
 	    ld (de), a
@@ -282,20 +275,17 @@ map_process_2:
 	    ld a, (hl)		; Next 16K. Leave the common for the task
 	    out (0xFE), a	; switcher
 	    ld (de), a
+	    pop af
 	    pop de
-				; NOTE: map_restore relies on the HL for
-				; exit of this
             ret
 ;
 ;	Restore a saved mapping. We are guaranteed that we won't switch
 ;	common copy between save and restore. Preserve all registers
 ;
 map_restore:
 	    push hl
-	    push af
 	    ld hl,#map_savearea
 	    call map_process_2	; Put the mapper back right
-	    pop af
 	    pop hl
 	    ret
 ;
@@ -313,6 +303,8 @@ map_table:
 	    .db 0,0,0,0	
 map_savearea:
 	    .db 0,0,0,0
+map_kernel_data:
+	    .db 3,2,1,4
 
 ; emulator debug port for now
 outchar:

Kernel/platform-msx2/vdp.s

@@ -16,6 +16,7 @@
 	    .globl _vdpport
 
 	    .globl vdpinit
+	    .globl platform_interrupt_all
 
 	    .area _CODE
 ;
@@ -282,3 +283,14 @@ _cursor_off:
 	    .area _DATA
 cursorpos:  .dw 0
 cursorpeek: .db 0
+
+	    .area _COMMONMEM
+
+;
+;	FIXME: should use vdpport, but right now vdpport is in data not
+;	common space.
+;
+platform_interrupt_all:
+	    ld c, #0x99
+	    in a, (c)
+	    ret