From a3d8829be92032d262cbea686c400a098e9e5242 Mon Sep 17 00:00:00 2001
From: Christian Groessler <chris@groessler.org>
Date: Fri, 17 Mar 2017 21:42:51 +0100
Subject: [PATCH] Creativison changes.

This change includes some cleanups, removal of mainargs.s (game console
programs never have arguments), and a workaround for a problem I'm seeing.

The problem is that sometimes (in fact, more often than not) the clrscr()
call in testcode/lib/joy-test.c writes some garbage chars on the screen (most
often a "P"). Could be my hardware (I haven't seen it on MAME), but to
me the root cause is still unknown.
---
 asminc/creativision.inc        |  7 ++++---
 cfg/creativision.cfg           |  2 +-
 libsrc/creativision/clrscr.s   |  6 +++---
 libsrc/creativision/cputc.s    |  6 +++---
 libsrc/creativision/crt0.s     | 15 ++++++++++-----
 libsrc/creativision/mainargs.s | 22 ----------------------
 6 files changed, 21 insertions(+), 37 deletions(-)
 delete mode 100644 libsrc/creativision/mainargs.s

diff --git a/asminc/creativision.inc b/asminc/creativision.inc
index 83a63ba07..49d55a342 100644
--- a/asminc/creativision.inc
+++ b/asminc/creativision.inc
@@ -10,10 +10,10 @@ CURSOR_X                = $3C
 CURSOR_Y                = $3D
 
 ;** VDP
-VDP_CONTROL_W           = $3001
-VDP_DATA_W              = $3000
-VDP_STATUS_R            = $2001
 VDP_DATA_R              = $2000
+VDP_STATUS_R            = $2001
+VDP_DATA_W              = $3000
+VDP_CONTROL_W           = $3001
 
 ;** PIA
 PIA0_DATA               = $1000
@@ -58,3 +58,4 @@ JOY_NNW                 = $4A
 BIOS_IRQ1_ADDR          = $FF3F
 BIOS_IRQ2_ADDR          = $FF52
 BIOS_NMI_RESET_ADDR     = $F808
+BIOS_WRITE_VDP_REG      = $FE1F
diff --git a/cfg/creativision.cfg b/cfg/creativision.cfg
index 06e39b36f..9e4ecd8ce 100644
--- a/cfg/creativision.cfg
+++ b/cfg/creativision.cfg
@@ -4,7 +4,7 @@ SYMBOLS {
 MEMORY {
     ZP:  file = "", define = yes, start = $0020, size = $00E0;
     RAM: file = "", define = yes, start = $01FA, size = $0206;
-    ROM: file = %O, define = yes, start = $B000, size = $1000;
+    ROM: file = %O, define = yes, start = $B000, size = $1000, fill = yes, fillval = $FF;
 }
 SEGMENTS {
     ZEROPAGE: load = ZP,             type = zp;
diff --git a/libsrc/creativision/clrscr.s b/libsrc/creativision/clrscr.s
index 9e7238345..3c4856446 100644
--- a/libsrc/creativision/clrscr.s
+++ b/libsrc/creativision/clrscr.s
@@ -18,7 +18,7 @@ _clrscr:
         lda     #$50    ; VRAM offset high ($10 OR $40)
         sta     VDP_CONTROL_W
 
-        lda     #$C0    ; Space from ROM setup
+        lda     #$40    ; Space char from ROM setup
 
         ldx     #0
         ldy     #3
@@ -34,8 +34,8 @@ L1:     sta     VDP_DATA_W
         lda     #0
         sta     CURSOR_X
         sta     CURSOR_Y
-        sta     <SCREEN_PTR
+        sta     SCREEN_PTR
         lda     #$10
-        sta      >SCREEN_PTR
+        sta     SCREEN_PTR+1
 
         rts
diff --git a/libsrc/creativision/cputc.s b/libsrc/creativision/cputc.s
index ff60494b9..437b738b2 100644
--- a/libsrc/creativision/cputc.s
+++ b/libsrc/creativision/cputc.s
@@ -96,8 +96,8 @@ BAD_CHAR:
         jmp     plot
 
 ;-----------------------------------------------------------------------------
-; Initialize the conio subsystem. Code goes into the INIT segment, which may
-; be reused after startup.
+; Initialize the conio subsystem. "INIT" segment is nothing special on the
+; Creativision, it is part of the "ROM" memory.
 
 .segment        "INIT"
 
@@ -122,4 +122,4 @@ LL:     lda     boxchars,x
         bne     LL
 
         cli
-        jmp plot
+        jmp     plot
diff --git a/libsrc/creativision/crt0.s b/libsrc/creativision/crt0.s
index 420ac71ef..5185ff237 100644
--- a/libsrc/creativision/crt0.s
+++ b/libsrc/creativision/crt0.s
@@ -31,9 +31,6 @@ entry:
         ldx     #<__RAM_START__ - 1
         txs
 
-        ; Start interrupts
-        cli
-
         ; Clear the BSS data
         jsr     zerobss
 
@@ -49,13 +46,21 @@ entry:
         ; Call module constructors
         jsr     initlib
 
+        ; enable vertical blank interrupts in the display controller
+        lda      #$E0           ; 16K RAM, Active Display, Mode 1, VBI enabled
+        ldx      #$01           ; Register 1
+        jsr      BIOS_WRITE_VDP_REG
+
+        ; Start interrupts
+        cli
+
         ; Call main()
         jsr     callmain
 
         ; Call module destructors. This is also the _exit entry.
 _exit:  jsr     donelib
 
-        ; TODO: Replace with some sort of reset
+        ; A Creativision program isn't supposed to exit.
 loop:   jmp loop
 
 ; ------------------------------------------------------------------------
@@ -81,7 +86,7 @@ irq2:   jmp     BIOS_IRQ2_ADDR
         ; VDP Setup
         ; This sets to Graphics Mode 1
         .byte   $00             ; Register 0
-        .byte   $E0             ; Register 1 16K RAM, Active Display, Mode 1, VBI enabled
+        .byte   $C0             ; Register 1 16K RAM, Active Display, Mode 1, VBI disabled
         .byte   $04             ; Register 2 Name Table at $1000 - $12FF
         .byte   $60             ; Register 3 Colour Table at $1800 - $181F
         .byte   $00             ; Register 4 Pattern Table at $0000 - $07FF
diff --git a/libsrc/creativision/mainargs.s b/libsrc/creativision/mainargs.s
deleted file mode 100644
index cda76d8d0..000000000
--- a/libsrc/creativision/mainargs.s
+++ /dev/null
@@ -1,22 +0,0 @@
-;
-; Ullrich von Bassewitz, 2003-03-07
-;
-; Setup arguments for main
-;
-
-
-        .constructor    initmainargs, 24
-        .import         __argc, __argv
-
-
-;---------------------------------------------------------------------------
-; Get possible command-line arguments. Goes into the special INIT segment,
-; which may be reused after the startup code is run
-
-.segment        "INIT"
-
-.proc   initmainargs
-
-        rts
-
-.endproc