diff --git a/doc/notes.txt b/doc/notes.txt
index ff0d7181..ff33b28b 100644
--- a/doc/notes.txt
+++ b/doc/notes.txt
@@ -65,7 +65,7 @@ TODO:
 - click to break on raster position
 - restructure folders
 - update memory browser window if view before 1st compile, update symbols
-- spinner disappears sometimes
+- spinner disappears sometimes (and compiles even when not spinning...)
 
 
 WEB WORKER FORMAT
diff --git a/index.html b/index.html
index e68ea79c..e9e8d81e 100644
--- a/index.html
+++ b/index.html
@@ -195,6 +195,10 @@ if (window.location.host.endsWith('8bitworkshop.com')) {
     <button id="replay_max" type="submit" title="End of replay"><span class="glyphicon glyphicon-fast-forward" aria-hidden="true"></span></button>
    </div>
   </div>
+  <div id="error_alert" class="alert alert-danger alert-dismissable" style="position:absolute;right:0;top:0;display:none">
+    <!--<button type="button" class="close" data-dismiss="alert" aria-hidden="true">&times;</button>-->
+    <div id="error_alert_msg"></div>
+  </div>
 </div>
 <!--
 <div class="twitbtn">
diff --git a/presets/astrocade/bios.c b/presets/astrocade/bios.c
new file mode 100644
index 00000000..99a72d76
--- /dev/null
+++ b/presets/astrocade/bios.c
@@ -0,0 +1,452 @@
+
+
+#define TEST
+
+#include <string.h>
+
+typedef unsigned char byte;
+typedef signed char sbyte;
+typedef unsigned short word;
+typedef signed short sword;
+
+/// HARDWARE
+
+__sfr __at(0x00) hw_col0r;	// palette 0
+__sfr __at(0x01) hw_col1r;
+__sfr __at(0x02) hw_col2r;
+__sfr __at(0x03) hw_col3r;
+__sfr __at(0x04) hw_col0l;
+__sfr __at(0x05) hw_col1l;
+__sfr __at(0x06) hw_col2l;
+__sfr __at(0x07) hw_col3l;	// palette 7
+
+__sfr __at(0x09) hw_horcb;	// horiz color boundary
+__sfr __at(0x0a) hw_verbl;	// vertical blanking line * 2
+__sfr __at(0x0c) hw_magic;	// magic register
+__sfr __at(0x0e) hw_inmod;	// interrupt enable
+__sfr __at(0x19) hw_xpand;	// expander register
+
+__sfr __at(0x08) hw_intst;	// intercept test feedback
+
+__sfr __at(0x10) hw_p1ctrl;	// player controls
+__sfr __at(0x11) hw_p2ctrl;	// player controls
+__sfr __at(0x12) hw_p3ctrl;	// player controls
+__sfr __at(0x13) hw_p4ctrl;	// player controls
+
+#define M_SHIFT0	0x00
+#define M_SHIFT1	0x01
+#define M_SHIFT2	0x02
+#define M_SHIFT3	0x03
+#define M_XPAND		0x08
+#define M_MOVE		0x00
+#define M_OR		0x10
+#define M_XOR		0x20
+#define M_FLOP		0x40
+#define M_SHIFT(x)	((x)&3)
+#define XPAND_COLORS(off,on) (((off)&3) | (((on)&3)<<2))
+
+/// GRAPHICS FUNCTIONS
+
+#define VHEIGHT 89	// number of scanlines
+#define VBWIDTH 40	// number of bytes per scanline
+#define PIXWIDTH 160	// 4 pixels per byte
+
+#define EXIT_CLIPDEST(addr) if ((((word)addr)&0xfff) >= 0xe10) return
+
+byte __at (0x0000) vmagic[VHEIGHT][VBWIDTH];
+byte __at (0x4000) vidmem[VHEIGHT][VBWIDTH];
+
+// Used by MUSIC PROCESSOR:
+word MUZPC;   //     $4FCE   // MUSic Program Counter
+word MUZSP;   //     $4FD0   // MUSic Stack Pointer
+byte PVOLAB;  //     $4FD2   // Preset VOLume for tones A and B
+byte PVOLMC;  //     $4FD3   // Preset VOLuMe for tone C and Noise Mode
+byte VOICES;  //     $4FD4   // music VOICES mask
+// COUNTER TIMERS (used by DECCTS,ACTINT,CTIMER):
+byte CT[8];
+// Used by SENTRY to track controls:
+byte CNT;     //     $4FDD   // Counter update & Number Tracking
+byte SEMI4S;  //     $4FDE   // SEMAPHORE flag bitS
+byte OPOT[4]; //     $4FDF   // Old POT 0 tracking byte
+byte KEYSEX;  //     $4FE3   // KEYS-EX tracking byte
+byte OSW[4];  //     $4FE4   // Old SWitch 0 tracking byte
+byte COLLST;  //     $4FE8   // COLset LaST address for P.B. A
+// Used by STIMER:
+byte DURAT;   //     $4FEA   // note DURATion
+byte TMR60;   //     $4FEB   // TiMeR for SIXTY'ths of sec
+byte TIMOUT;  //     $4FEC   // TIMer for blackOUT
+byte GTSECS;  //     $4FED   // Game Time SECondS
+byte GTMINS;  //     $4FEE   // Game Time MINuteS
+// Used by MENU:
+long RANSHT;  //     $4FEF   // RANdom number SHifT register
+byte NUMPLY;  //     $4FF3   // NUMber of PLaYers
+byte ENDSCR[3];  //     $4FF4   // END SCoRe to 'play to'
+byte MRLOCK;  //     $4FF7   // Magic Register LOCK out flag
+byte GAMSTB;  //     $4FF8   // GAMe STatus Byte
+byte PRIOR;   //     $4FF9   // PRIOR music protect flag
+byte SENFLG;  //     $4FFA   // SENtry control seizure FLaG
+// User UPI Routines, even numbers from $80 to $FE ( + 1 for SUCK):
+byte* UMARGT;  //     $4FFB   // User Mask ARGument Table + (routine / 2)
+word* USERTB;  //     $4FFD   // USER Table Base + routine = JumP address
+
+// start routine @ 0x0
+void bios_start()  __naked {
+__asm
+        DI
+        LD	SP,#0x4fce
+  	CALL	_bios_init
+        LD	HL,#0x2005
+        LD	A,(HL)
+        INC	HL
+#ifndef TEST
+        LD	H,(HL)
+        LD	L,A
+        JP	(HL)
+#else
+  	jp	_main
+#endif
+    	.ds	0x38 - 0xf	; skip to 0x38
+__endasm;
+}
+
+void interrupt_0x38() __naked {
+__asm
+  	push	hl
+  	push	af
+  	push	bc
+  	push	de
+  	push	ix
+  	push	iy
+  	ld	hl,#0
+  	add	hl,sp
+  	push	hl
+  	call	_SYSCALL
+  	pop	hl
+  	pop	iy
+  	pop	ix
+  	pop	de
+  	pop	bc
+  	pop	af
+  	pop	hl
+  	ret
+__endasm;
+}
+
+void _predope() __naked {
+__asm
+    	.ds	0x200-0x52	; skip to 0x200
+__endasm;
+}
+
+// DOPE vector @ 0x200
+void DOPE()  __naked {
+__asm
+  	JP	_STIMER
+  	JP	_CTIMER
+__endasm;
+}
+
+// TODO: font defs
+
+void STIMER() {
+}
+
+void CTIMER() {
+}
+
+void bios_init() {
+  memset((void*)0x4fce, 0, 0x5000-0x4fce);
+}
+
+///// INTERPRETER
+
+typedef struct {
+  union {
+    struct {
+      word iy,ix,de,bc,af,hl;
+    } w;
+    struct {
+      byte iyl,iyh,ixl,ixh,e,d,c,b,f,a,l,h;
+    } b;
+  } regs;
+  byte* params;
+} ContextBlock;
+
+#define REG_IY	0x1
+#define REG_E	0x2
+#define REG_D	0x4
+#define REG_C	0x8
+#define REG_B	0x10
+#define REG_IX  0x20
+#define REG_A	0x40
+#define REG_HL	0x80
+#define REG_DE	(REG_D|REG_E)
+#define REG_BC	(REG_B|REG_C)
+
+typedef void (Routine)();
+typedef void (SysRoutine)(ContextBlock *ctx);
+
+typedef struct {
+  SysRoutine* routine;
+  byte argmask;
+} SysCallEntry;
+
+void SYSCALL(ContextBlock *ctx);
+
+void INTPC(ContextBlock *ctx) {
+  while (ctx->params[0] != 2) { // 2 = exit
+    SYSCALL(ctx);
+  }
+}
+
+// never called, hopefully
+void EXIT(ContextBlock *ctx) {
+  ctx;
+}
+
+// jumps to HL
+void RCALL(ContextBlock *ctx) {
+  ((Routine*)ctx->regs.w.hl)();
+}
+
+// Outputs D to port 0A, B to port 09, A to port 0E.
+void SETOUT(ContextBlock *ctx) {
+  hw_verbl = ctx->regs.b.d;
+  hw_horcb = ctx->regs.b.b;
+  hw_inmod = ctx->regs.b.a;
+}
+
+// sets color palettes from (HL)
+void COLSET(ContextBlock *ctx) {
+  byte* palette = (byte*) ctx->regs.w.hl;
+  hw_col0r = *palette++;
+  hw_col1r = *palette++;
+  hw_col2r = *palette++;
+  hw_col3r = *palette++;
+  hw_col0l = *palette++;
+  hw_col1l = *palette++;
+  hw_col2l = *palette++;
+  hw_col3l = *palette++;
+}
+
+// Stores A in BC bytes starting at location DE.
+void FILL(ContextBlock *ctx) {
+  byte* dest = (byte*) ctx->regs.w.de;
+  word count = ctx->regs.w.bc;
+  byte val = ctx->regs.b.a;
+  memset(dest, val, count);
+}
+
+#define LOCHAR 32
+#define HICHAR 127
+#define FONT_BWIDTH 1
+#define FONT_HEIGHT 8
+const char FONT[HICHAR-LOCHAR+1][FONT_HEIGHT*FONT_BWIDTH] = {
+{ 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, },{ 0x00,0x00,0x00,0x20,0x20,0x20,0x00,0x20, },{ 0x00,0x00,0x50,0x50,0x50,0x00,0x00,0x00, },{ 0x00,0x00,0x00,0x50,0xF8,0x50,0xF8,0x50, },{ 0x00,0x00,0x00,0xF8,0xA0,0xF8,0x28,0xF8, },{ 0x00,0x00,0x00,0xC8,0xD0,0x20,0x58,0x98, },{ 0x00,0x00,0x00,0xE0,0xA8,0xF8,0x90,0xF8, },{ 0x00,0x00,0x40,0x40,0x40,0x00,0x00,0x00, },{ 0x00,0x00,0x30,0x20,0x20,0x20,0x20,0x20, },{ 0x00,0x00,0x60,0x20,0x20,0x20,0x20,0x20, },{ 0x00,0x00,0x00,0x20,0xA8,0x70,0xA8,0x20, },{ 0x00,0x00,0x00,0x20,0x20,0xF8,0x20,0x20, },{ 0x00,0x00,0x00,0x00,0x00,0x00,0x60,0x60, },{ 0x00,0x00,0x00,0x00,0x00,0xF8,0x00,0x00, },{ 0x00,0x00,0x00,0x00,0x00,0x00,0x60,0x60, },{ 0x00,0x00,0x00,0x08,0x10,0x20,0x40,0x80, },{ 0x00,0x00,0x00,0xF8,0x88,0xE8,0x88,0xF8, },{ 0x00,0x00,0x00,0x10,0x30,0x50,0x10,0x10, },{ 0x00,0x00,0x00,0xF8,0x08,0xF8,0x80,0xF8, },{ 0x00,0x00,0x00,0xF8,0x08,0xF8,0x08,0xF8, },{ 0x00,0x00,0x00,0x38,0x48,0x88,0xF8,0x08, },{ 0x00,0x00,0x00,0xF8,0x80,0xF8,0x08,0xF8, },{ 0x00,0x00,0x00,0xF8,0x80,0xF8,0x88,0xF8, },{ 0x00,0x00,0x00,0xF8,0x08,0x10,0x20,0x40, },{ 0x00,0x00,0x00,0xF8,0x88,0xF8,0x88,0xF8, },{ 0x00,0x00,0x00,0xF8,0x88,0xF8,0x08,0xF8, },{ 0x00,0x00,0x00,0x30,0x30,0x00,0x30,0x30, },{ 0x00,0x00,0x00,0x30,0x30,0x00,0x30,0x30, },{ 0x00,0x00,0x08,0x10,0x20,0x40,0x20,0x10, },{ 0x00,0x00,0x00,0x00,0xF8,0x00,0xF8,0x00, },{ 0x00,0x00,0x40,0x20,0x10,0x08,0x10,0x20, },{ 0x00,0x00,0x00,0xF8,0x08,0x78,0x00,0x60, },{ 0x00,0x00,0x00,0xF8,0xA8,0xB8,0x80,0xF8, },{ 0x00,0x00,0x00,0xF8,0x88,0xF8,0x88,0x88, },{ 0x00,0x00,0x00,0xF0,0x90,0xF8,0x88,0xF8, },{ 0x00,0x00,0x00,0xF8,0x80,0x80,0x80,0xF8, },{ 0x00,0x00,0x00,0xE0,0x90,0x88,0x88,0xF8, },{ 0x00,0x00,0x00,0xF8,0x80,0xF8,0x80,0xF8, },{ 0x00,0x00,0x00,0xF8,0x80,0xF8,0x80,0x80, },{ 0x00,0x00,0x00,0xF8,0x80,0xB8,0x88,0xF8, },{ 0x00,0x00,0x00,0x88,0x88,0xF8,0x88,0x88, },{ 0x00,0x00,0x00,0x40,0x40,0x40,0x40,0x40, },{ 0x00,0x00,0x00,0x08,0x08,0x88,0x88,0xF8, },{ 0x00,0x00,0x00,0x88,0x90,0xA0,0x90,0x88, },{ 0x00,0x00,0x00,0x80,0x80,0x80,0x80,0xF8, },{ 0x00,0x00,0x00,0xFE,0x92,0x92,0x92,0x92, },{ 0x00,0x00,0x00,0x88,0xC8,0xA8,0x98,0x88, },{ 0x00,0x00,0x00,0xF8,0x88,0x88,0x88,0xF8, },{ 0x00,0x00,0x00,0xF8,0x88,0x88,0xF8,0x80, },{ 0x00,0x00,0x00,0xF8,0x88,0xA8,0xA8,0xF8, },{ 0x00,0x00,0x00,0xF8,0x88,0xF8,0x90,0x88, },{ 0x00,0x00,0x00,0xF8,0x80,0xF8,0x08,0xF8, },{ 0x00,0x00,0x00,0xF8,0x20,0x20,0x20,0x20, },{ 0x00,0x00,0x00,0x88,0x88,0x88,0x88,0xF8, },{ 0x00,0x00,0x00,0x88,0x88,0x90,0xA0,0xC0, },{ 0x00,0x00,0x00,0x92,0x92,0x92,0x92,0xFE, },{ 0x00,0x00,0x00,0x88,0x50,0x20,0x50,0x88, },{ 0x00,0x00,0x00,0x88,0x88,0xF8,0x08,0xF8, },{ 0x00,0x00,0x00,0xF8,0x10,0x20,0x40,0xF8, },{ 0x00,0x00,0x38,0x20,0x20,0x20,0x20,0x20, },{ 0x00,0x00,0x00,0x80,0x40,0x20,0x10,0x08, },{ 0x00,0x00,0x70,0x10,0x10,0x10,0x10,0x10, },{ 0x00,0x00,0x00,0x20,0x50,0x88,0x00,0x00, },{ 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, },{ 0x00,0x00,0x40,0x20,0x10,0x00,0x00,0x00, },{ 0x00,0x00,0x00,0xF8,0x88,0xF8,0x88,0x88, },{ 0x00,0x00,0x00,0xF0,0x90,0xF8,0x88,0xF8, },{ 0x00,0x00,0x00,0xF8,0x80,0x80,0x80,0xF8, },{ 0x00,0x00,0x00,0xE0,0x90,0x88,0x88,0xF8, },{ 0x00,0x00,0x00,0xF8,0x80,0xF8,0x80,0xF8, },{ 0x00,0x00,0x00,0xF8,0x80,0xF8,0x80,0x80, },{ 0x00,0x00,0x00,0xF8,0x80,0xB8,0x88,0xF8, },{ 0x00,0x00,0x00,0x88,0x88,0xF8,0x88,0x88, },{ 0x00,0x00,0x00,0x40,0x40,0x40,0x40,0x40, },{ 0x00,0x00,0x00,0x08,0x08,0x88,0x88,0xF8, },{ 0x00,0x00,0x00,0x88,0x90,0xA0,0x90,0x88, },{ 0x00,0x00,0x00,0x80,0x80,0x80,0x80,0xF8, },{ 0x00,0x00,0x00,0xFE,0x92,0x92,0x92,0x92, },{ 0x00,0x00,0x00,0x88,0xC8,0xA8,0x98,0x88, },{ 0x00,0x00,0x00,0xF8,0x88,0x88,0x88,0xF8, },{ 0x00,0x00,0x00,0xF8,0x88,0x88,0xF8,0x80, },{ 0x00,0x00,0x00,0xF8,0x88,0xA8,0xA8,0xF8, },{ 0x00,0x00,0x00,0xF8,0x88,0xF8,0x90,0x88, },{ 0x00,0x00,0x00,0xF8,0x80,0xF8,0x08,0xF8, },{ 0x00,0x00,0x00,0xF8,0x20,0x20,0x20,0x20, },{ 0x00,0x00,0x00,0x88,0x88,0x88,0x88,0xF8, },{ 0x00,0x00,0x00,0x88,0x88,0x90,0xA0,0xC0, },{ 0x00,0x00,0x00,0x92,0x92,0x92,0x92,0xFE, },{ 0x00,0x00,0x00,0x88,0x50,0x20,0x50,0x88, },{ 0x00,0x00,0x00,0x88,0x88,0xF8,0x08,0xF8, },{ 0x00,0x00,0x00,0xF8,0x10,0x20,0x40,0xF8, },{ 0x00,0x00,0x38,0x20,0x20,0xE0,0x20,0x20, },{ 0x00,0x00,0x20,0x20,0x20,0x20,0x20,0x20, },{ 0x00,0x00,0xE0,0x20,0x20,0x38,0x20,0x20, },{ 0x00,0x00,0x00,0xE8,0xB8,0x00,0x00,0x00, },{ 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, },};
+
+// draw a letter
+void draw_char(byte ch, byte x, byte y, byte op) {
+  const byte* src = &FONT[(ch-LOCHAR)][0];
+  byte xb = x>>2;		// divide x by 4
+  byte* dest = &vmagic[y][xb];	// destination address
+  hw_magic = M_SHIFT(x) | M_XPAND | op;
+  for (byte i=0; i<8; i++) {
+    char b = *src++;
+    EXIT_CLIPDEST(dest);
+    *dest++ = b;	// expand lower nibble -> 1st byte
+    *dest++ = b;	// expand upper nibble -> 2nd byte
+    *dest++ = 0;	// leftover -> 3rd byte
+    *dest = 0;		// reset upper/lower flag
+    dest += VBWIDTH-3;	// we incremented 3 bytes for this line
+  }
+}
+
+void draw_string(const char* str, byte x, byte y, byte op) {
+  do {
+    byte ch = *str++;
+    if (!ch) break;
+    draw_char(ch, x, y, op);
+    x += 8;
+  } while (1);
+}
+
+// String display routine
+void STRDIS(ContextBlock *ctx) {
+  byte opts = ctx->regs.b.c;
+  byte x = ctx->regs.b.e;
+  byte y = ctx->regs.b.d;
+  char* str = (char*) ctx->regs.w.hl;
+  void* fontdesc = (void*) ctx->regs.w.ix;
+  hw_xpand = opts & 0xf;
+  draw_string(str, x, y, 3&(opts>>4)); // TODO: opts
+}
+
+// Character display routine
+void CHRDIS(ContextBlock *ctx) {
+  char chstr[2];
+  chstr[0] = ctx->regs.b.a;
+  chstr[1] = 0;
+  ctx->regs.w.hl = (word) &chstr;
+  STRDIS(ctx);
+}
+
+const SysCallEntry SYSCALL_TABLE[64] = {
+  /* 0 */
+  { &INTPC,	0 },
+  { &EXIT,	0 },
+  { &RCALL,	REG_HL },
+  { 0, 0 },
+  { 0, 0 },
+  /* 10 */
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  /* 20 */
+  { 0, 0 },
+  { &SETOUT,	REG_D|REG_B|REG_A },
+  { &COLSET,	REG_HL },
+  { &FILL,	REG_A|REG_BC|REG_DE },
+  { 0, 0 },
+  /* 30 */
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  /* 40 */
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  /* 50 */
+  { &CHRDIS,	REG_E|REG_D|REG_C|REG_A },
+  { &STRDIS,	REG_E|REG_D|REG_C|REG_HL },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  /* 60 */
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  /* 70 */
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  /* 80 */
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  /* 90 */
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  /* 100 */
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  /* 110 */
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  /* 120 */
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+  { 0, 0 },
+};
+
+void suckParams(ContextBlock *ctx, byte argmask) {
+  byte* dest = (byte*) ctx;
+  byte* src = ctx->params;
+  if (argmask & REG_IX) {
+    ctx->regs.b.ixl = *src++;
+    ctx->regs.b.ixh = *src++;
+  }
+  if (argmask & REG_E)
+    ctx->regs.b.e = *src++;
+  if (argmask & REG_D)
+    ctx->regs.b.d = *src++;
+  if (argmask & REG_C)
+    ctx->regs.b.c = *src++;
+  if (argmask & REG_B)
+    ctx->regs.b.b = *src++;
+  if (argmask & REG_A)
+    ctx->regs.b.a = *src++;
+  if (argmask & REG_HL) {
+    ctx->regs.b.l = *src++;
+    ctx->regs.b.h = *src++;
+  }
+  ctx->params = src;
+}
+
+void SYSCALL(ContextBlock *ctx) {
+  byte op = *ctx->params++;
+  byte argmask;
+  SysRoutine* routine;
+  // user-defined?
+  if (op & 0x80) {
+    argmask = UMARGT[op & 0x7f];
+    routine = (SysRoutine*) USERTB[op & 0x7f];
+  } else {
+    const SysCallEntry* entry = &SYSCALL_TABLE[op>>1];
+    argmask = entry->argmask;
+    routine = entry->routine;
+  }
+  // suck params into context block?
+  if (op & 1) {
+    suckParams(ctx, argmask);
+  }
+  // call the routine
+  if (routine) {
+    routine(ctx);
+  }
+}
+
+#ifdef TEST
+void main() {
+__asm
+	RST	0x38
+  	.db	0	; INTPC
+  	.db	22+1	; SETOUT
+        .db	102*2, 0x1c, 0x08
+        .db	24+1	; COLSET
+        .dw	_main   ; palette???
+        .db	26+1	; FILL
+        .dw	0x4000
+        .dw	90*40
+        .db	0xaa
+        .db	52+1	; draw string
+        .db	0
+        .db	32
+        .db	0x0c
+        .dw	HelloString
+        .db	50+1	; draw char
+        .db	0
+        .db	64
+        .db	0x0c
+        .db	65
+        .db	2	; EXIT
+        jp	.end
+HelloString:
+        .ascii	"HELLO WORLD!"
+        .db 0
+.end:
+__endasm;
+  	while (1) CT[0]++;
+}
+#endif
diff --git a/src/baseplatform.ts b/src/baseplatform.ts
index 3093ee85..f6c13970 100644
--- a/src/baseplatform.ts
+++ b/src/baseplatform.ts
@@ -523,8 +523,8 @@ export abstract class BaseZ80Platform extends BaseDebugPlatform {
     switch (category) {
       case 'CPU':   return cpuStateToLongString_Z80(state.c);
       case 'Stack': {
-        var sp = state.c.SP;
-        var start = ((sp-1) & 0xff00);
+        var sp = state.c.SP-1;
+        var start = sp & 0xff00;
         var end = start + 0xff;
         if (sp == 0) sp = 0x10000;
         return dumpStackToString(<Platform><any>this, [], start, end, sp, 0xcd);
@@ -897,7 +897,7 @@ export function dumpStackToString(platform:Platform, mem:number[], start:number,
     } else {
       if (nraw == 0)
         s += "\n$" + hex(sp) + ": ";
-      s += hex(read(sp+1)) + " ";
+      s += hex(read(sp)) + " ";
       if (++nraw == 8) nraw = 0;
     }
   }
diff --git a/src/platform/astrocade.ts b/src/platform/astrocade.ts
index b9d4f6e3..c82b809b 100644
--- a/src/platform/astrocade.ts
+++ b/src/platform/astrocade.ts
@@ -172,7 +172,7 @@ const _BallyAstrocadePlatform = function(mainElement, arcade) {
 
   start = function() {
     ram = new RAM(arcade ? 0x5000 : 0x1000);
-    var lzgrom = window['ASTROCADE_LZGROM'];
+    var lzgrom = window['ASTROCADE_LZGROM'] || window['ASTROCADE_BIOS_LZG'];
     if (lzgrom)
       bios = new lzgmini().decode(stringToByteArray(atob(lzgrom)));
     else
@@ -320,6 +320,11 @@ const _BallyAstrocadePlatform = function(mainElement, arcade) {
     this.reset();
   }
 
+  loadBIOS(title, data) {
+    bios = padBytes(data, 0x2000);
+    this.reset();
+  }
+
   loadState(state) {
     cpu.loadState(state.c);
     ram.mem.set(state.b);
@@ -426,9 +431,16 @@ const _BallyArcadePlatform = function(mainElement) {
   this.loadControlsState(_in);
 }
 
+const _BallyAstrocadeBIOSPlatform = function(mainElement) {
+  this.__proto__ = new (_BallyAstrocadePlatform as any)(mainElement);
+
+  this.loadROM = this.loadBIOS;
+}
+
 /////
 
 PLATFORMS['astrocade'] = _BallyAstrocadePlatform;
+PLATFORMS['astrocade-bios'] = _BallyAstrocadeBIOSPlatform;
 PLATFORMS['astrocade-arcade'] = _BallyArcadePlatform;
 
 //http://glankonian.com/~lance/astrocade_palette.html
@@ -439,3 +451,5 @@ for (var i=0; i<256; i++) {
   x = ((x&0xff)<<16) | ((x>>16)&0xff) | (x&0x00ff00);
   ASTROCADE_PALETTE[i] = x | 0xff000000;
 }
+
+//var ASTROCADE_BIOS_LZG = decodeURIComponent();
diff --git a/src/project.ts b/src/project.ts
index 08e6a8c1..2c82fe9b 100644
--- a/src/project.ts
+++ b/src/project.ts
@@ -258,8 +258,8 @@ export class CodeProject {
   
   processBuildResult(data:WorkerResult) {
     // TODO: link listings with source files
-    this.listings = data.listings;
-    if (this.listings) {
+    if (data.listings) {
+      this.listings = data.listings;
       for (var lstname in this.listings) {
         var lst = this.listings[lstname];
         if (lst.lines)
diff --git a/src/tools/uifont.ts b/src/tools/uifont.ts
index f2ff51a1..9d4c119c 100644
--- a/src/tools/uifont.ts
+++ b/src/tools/uifont.ts
@@ -13,6 +13,7 @@ var FONT_DEFAULT_PARAMS = {
     wbytes:1,
     width:8,
     height:8,
+    yoffset:0,
     lochar:32,
     hichar:127,
     rotate:false,
@@ -36,6 +37,7 @@ var FONT_PRESETS = {
        vcs: { output:'dasm', msbfirst:true },
   mw8080bw: { rotate:true, flip:true, msbfirst:true },
        nes: { np:2, msbfirst:true },
+ astrocade: { output:'zmac', msbfirst:true },
 };
 
 function loadPreset(preset_id) {
@@ -58,6 +60,7 @@ function refreshToolbar(event?) {
       case 'height':
       case 'lochar':
       case 'hichar':
+      case 'yoffset':
         params[event.item.id] = parseInt(event.item.value);
         break;
       case 'rotate':
@@ -78,6 +81,10 @@ function refreshToolbar(event?) {
         if (event.subItem)
           loadCharSel(event.subItem.id);
         break;
+      case 'output':
+        if (event.subItem)
+          params[event.item.id] = event.subItem.id;
+        break;
     }
   }
   // set derived params
@@ -172,19 +179,27 @@ function renderGlyph(glyph, putPixel) {
   var h = glyph.bbx[1];
   var dx = glyph.bbx[2];
   var dy = glyph.bbx[3];
+  var error_logged = false;
   for (var y=0; y<glyph.bytes.length; y++) {
       for (var x=0; x<w; x++) {
           if (glyph.bytes[glyph.bytes.length-y-1] & (0x800000 >> x)) {
               var xx = x+dx;
               var yy = y+dy;
+              yy += params.yoffset || 0;
               /*
               font.pixbounds[0] = Math.min(font.pixbounds[0], xx);
               font.pixbounds[1] = Math.min(font.pixbounds[1], yy);
               font.pixbounds[2] = Math.max(font.pixbounds[2], xx);
               font.pixbounds[3] = Math.max(font.pixbounds[3], yy);
               */
-              if (xx >= 0 && yy >= 0 && xx < params.width && yy < params.height)
+              var xoutrange = xx < 0 || x >= params.width;
+              var youtrange = yy < 0 || y >= params.width;
+              if (!xoutrange && !youtrange) {
                 putPixel(xx, yy);
+              } else if (!error_logged) {
+                errors.push((xoutrange?"X":"Y") + " out of range on character " + String.fromCharCode(glyph.ord) + " " + x + "," + y);
+                error_logged = true;
+              }
           }
       }
   }
@@ -244,12 +259,6 @@ function encodeGlyph(glyph, bytes) {
         }
         var xoutrange = (x <  0 || x >= params.width);
         var youtrange = (y <  0 || y >= params.height);
-        if (xoutrange || youtrange) {
-            if (!abort) {
-                errors.push((xoutrange?"X":"Y") + " out of range on character " + String.fromCharCode(glyph.ord) + " " + x + "," + y);
-                abort = true;
-            }
-        }
         var bpb = 8 / (params.bpp||1);
         var ofs = Math.floor(x/bpb) + (params.height-1-y)*params.wbytes;
         var bit = x % bpb;
@@ -260,7 +269,8 @@ function encodeGlyph(glyph, bytes) {
 
 function encodeFont() {
     var s = '';
-    if (params.output.startsWith('c_')) {
+    var c_output = params.output.startsWith('c_');
+    if (c_output) {
       //s += '/* ' + JSON.stringify(params) + JSON.stringify(font.bounds) + JSON.stringify(font.pixbounds) + ' */\n';
       s += "#define LOCHAR " + params.lochar + "\n";
       s += "#define HICHAR " + params.hichar + "\n";
@@ -268,9 +278,9 @@ function encodeFont() {
       s += "#define FONT_HEIGHT " + params.height + "\n";
       s += "const char FONT[HICHAR-LOCHAR+1][FONT_HEIGHT*FONT_BWIDTH] = {\n";
     } else {
-      s += "LOCHAR\t\t= " + params.lochar + "\n";
-      s += "HICHAR\t\t= " + params.hichar + "\n";
-      s += "FONT_HEIGHT\t= " + params.height + "\n";
+      s += "LOCHAR\t\tequ " + params.lochar + "\n";
+      s += "HICHAR\t\tequ " + params.hichar + "\n";
+      s += "FONT_HEIGHT\tequ " + params.height + "\n";
       s += "FontData:\n";
     }
     errors = [];
@@ -281,19 +291,23 @@ function encodeFont() {
             encodeGlyph(glyph, bytes);
             if (params.output=='c_nested') s += "{ ";
             else if (params.output=='dasm') s += "\thex\t";
+            else if (params.output=='zmac') s += "\tdb\t";
             for (var i=0; i<bytes.length; i++) {
-              if (params.output.startsWith('c_'))
-                s += "0x" + hex(bytes[i]) + ",";
-              else if (params.output == 'dasm')
+              if (params.output == 'dasm')
                 s += hex(bytes[i]);
+              else
+                s += "0x" + hex(bytes[i]) + ((i<bytes.length-1)?",":"");
             }
             if (params.output=='c_nested') s += " },";
-            if (!params.output.startsWith('c_') || params.newline) s += "\n";
+            if (!c_output || params.newline) s += "\n";
         }
     }
-    s += "};\n";
+    if (c_output) s += "};\n";
     while (errors.length) {
+      if (c_output)
         s = "/* " + errors.pop() + " */\n" + s;
+      else
+        s = ";; " + errors.pop() + "\n" + s;
     }
     return s;
 }
@@ -356,6 +370,7 @@ $().w2toolbar({
 			 { text: 'Midway 8080',   id: 'mw8080bw' }, 
 			 { text: 'NES',           id: 'nes' },
 			 { text: 'Apple ][',    	id: 'apple2' },
+			 { text: 'Astrocade',    	id: 'astrocade' },
 		  ]},
 		{ type: 'check',  id: 'rotate', caption: 'Rotate', img: 'fas fa-sync', tooltip: 'Rotate 90 degrees (swap X/Y)' },
 		{ type: 'check',  id: 'xflip', caption: 'Mirror', img: 'fas fa-arrows-alt-h', tooltip: 'Flip X axis' },
@@ -370,10 +385,19 @@ $().w2toolbar({
   		]},
 		{ type: 'html', id: 'width', html: toolbarHTMLItem('width','Width:',2) },
 		{ type: 'html', id: 'height', html: toolbarHTMLItem('height','Height:',2) },
+		{ type: 'html', id: 'yoffset', html: toolbarHTMLItem('yoffset','Y Offset:',2) },
+		{ type: 'menu-radio', id: 'output', caption: 'Output', img: 'icon-folder',
+		  tooltip: 'Output format',
+		  items: [
+			 { text: 'C array (nested)', id: 'c_nested' }, 
+			 { text: 'C array (flat)',   id: 'c_flat' }, 
+			 { text: 'Assembler (DASM)', id: 'dasm' }, 
+			 { text: 'Assembler (zmac)', id: 'zmac' },
+		  ]},
 		{ type: 'break', id: 'break1' },
-		{ type: 'menu-radio', id: 'charsel', caption: 'Characters', img: 'icon-folder', 
+		
+		{ type: 'menu-radio', id: 'charsel', caption: 'Chars', img: 'icon-folder', 
 		  tooltip: 'Range of characters to encode, from first to last',
-		  //text: function(item) { refreshCharSel(item); return item.caption; },
 		  items: [
 			 //{ text: 'ISO (256 chars)', value:'0-255' }, 
 			 { text: 'ASCII (upper only)', id:'32-95' }, 
diff --git a/src/ui.ts b/src/ui.ts
index e188a0dd..4b1ca752 100644
--- a/src/ui.ts
+++ b/src/ui.ts
@@ -5,7 +5,7 @@
 import $ = require("jquery");
 import * as bootstrap from "bootstrap";
 import { CodeProject } from "./project";
-import { WorkerResult, SourceFile } from "./workertypes";
+import { WorkerResult, SourceFile, WorkerError } from "./workertypes";
 import { ProjectWindows } from "./windows";
 import { Platform, Preset } from "./baseplatform";
 import { PLATFORMS } from "./emu";
@@ -95,6 +95,7 @@ function initProject() {
       toolbar.removeClass("is-busy");
       toolbar.removeClass("has-errors"); // may be added in next callback
       projectWindows.setErrors(null);
+      $("#error_alert").hide();
     }
     $('#compile_spinner').css('visibility', busy ? 'visible' : 'hidden');
   };
@@ -469,11 +470,24 @@ function updateSelector() {
   });
 }
 
+function showErrorAlert(errors : WorkerError[]) {
+  var div = $("#error_alert_msg").empty();
+  for (var err of errors.slice(0,10)) {
+    var s = '';
+    if (err.path) s += err.path + ":";
+    if (err.line) s += err.line + ":";
+    s += err.msg;
+    div.append($("<p>").text(s));
+  }
+  $("#error_alert").show();
+}
+
 function setCompileOutput(data: WorkerResult) {
   // errors? mark them in editor
   if (data.errors && data.errors.length > 0) {
-    projectWindows.setErrors(data.errors);
     toolbar.addClass("has-errors");
+    projectWindows.setErrors(data.errors);
+    showErrorAlert(data.errors);
   } else {
     // process symbol map
     symbolmap = data.symbolmap;
diff --git a/src/views.ts b/src/views.ts
index 1a42f1b9..378ac81f 100644
--- a/src/views.ts
+++ b/src/views.ts
@@ -496,7 +496,7 @@ export class DisassemblerView implements ProjectView {
   getCursorPC() : number {
     var line = this.disasmview.getCursor().line;
     if (line >= 0) {
-      var toks = this.disasmview.getLine(line).split(/\s+/);
+      var toks = this.disasmview.getLine(line).trim().split(/\s+/);
       if (toks && toks.length >= 1) {
         var pc = parseInt(toks[0], 16);
         if (pc >= 0) return pc;
diff --git a/src/worker/workermain.js b/src/worker/workermain.js
index 4993645c..01ce95c4 100644
--- a/src/worker/workermain.js
+++ b/src/worker/workermain.js
@@ -165,6 +165,13 @@ var PLATFORM_PARAMS = {
      data_size: 0x220,
      stack_end: 0x8000,
   },
+  'astrocade-bios': {
+    code_start: 0x0000,
+      rom_size: 0x2000,
+    data_start: 0x4fce,
+     data_size: 50,
+     stack_end: 0x4fce,
+  },
 };
 
 // shim out window and document objects for security
@@ -598,7 +605,7 @@ function assembleDASM(step) {
         unresolved[matches[1]] = 0;
       }
     } else if (s.startsWith("Warning:")) {
-      errors.push({line:1, msg:s.substr(9)});
+      errors.push({line:0, msg:s.substr(9)});
     }
   }
   var Module = DASM({
@@ -918,7 +925,7 @@ function assembleSDASZ80(step) {
       if (matches) {
         //var errline = parseInt(matches[2]);
         errors.push({
-          line:1, // TODO
+          line:0, // TODO
           path:step.path,
           msg:matches[1]
         });
diff --git a/tools/fontgen/index.html b/tools/fontgen/index.html
index d85fd9ee..83564d09 100644
--- a/tools/fontgen/index.html
+++ b/tools/fontgen/index.html
@@ -35,7 +35,7 @@ if (window.location.host.endsWith('8bitworkshop.com')) {
       <li>Select a font below (check out the search and filter options.)</li>
       <li>Choose a platform from the Presets menu, or choose your own encoding options.</li>
       <li>Select a range of characters to encode.</li>
-      <li>Check out the preview bitmap to make sure none of your characters are visibly cut off, or increase your height/width (if your platform supports it.)</li>
+      <li>If you have out-of-range errors you want to fix, adjust the Y Offset value, or increase your height/width (if your platform supports it.)</li>
       <li>Copy the output to the clipboard.</li>
       <li>Paste it into your code.</li>
     </ol>