Modify bsim 2.0.0 from MIT's Computation Structures (6.004) class to add video out.

bhack.js

$(".tty").prepend( '<div style="float: right;"><canvas id="television" width="192" height="128" style="background-color: lightblue;">xbetahack ERROR: html5 canvas is missing.</canvas></div>');

bhack = {
	tv: {
		canvas: null,
		width: 96,
		height: 64,
		pos: 0,
		
		fill: function(col) {
			var c = bhack.tv.canvas;
			var ctx = c.getContext("2d");
			ctx.fillStyle = col;
			ctx.fillRect(0, 0, c.width, c.height);
		},
		clear: function() {
			bhack.tv.fill("#FFF");
			bhack.tv.pos = 0;
		},
		set_pos: function(newpos) { bhack.tv.pos = newpos % (bhack.tv.width * bhack.tv.height); },
		out: function(color) {
			
			var tv = bhack.tv;
			var c = tv.canvas;
			var ctx = c.getContext("2d");

			var style = tv.palette[color];
			if(style) {
				ctx.fillStyle = style;
					
				var x = tv.pos % tv.width;
				var xs = c.width/tv.width;
				var y = Math.floor(tv.pos / tv.width);
				var ys = c.height/tv.height;
				ctx.fillRect(x * xs, y * ys, xs, ys);
			}
			
			tv.pos += 1;
			tv.pos = tv.pos % (tv.width * tv.height);
		},
		
		palette: [
			"rgb(124,124,124)",
			"rgb(0,0,252)",
			"rgb(0,0,188)",
			"rgb(68,40,188)",
			"rgb(148,0,132)",
			"rgb(168,0,32)",
			"rgb(168,16,0)",
			"rgb(136,20,0)",
			"rgb(80,48,0)",
			"rgb(0,120,0)",
			"rgb(0,104,0)",
			"rgb(0,88,0)",
			"rgb(0,64,88)",
			"rgb(0,0,0)",
			"rgb(0,0,0)",
			"rgb(0,0,0)",
			
			"rgb(188,188,188)",
			"rgb(0,120,248)",
			"rgb(0,88,248)",
			"rgb(104,68,252)",
			"rgb(216,0,204)",
			"rgb(228,0,88)",
			"rgb(248,56,0)",
			"rgb(228,92,16)",
			"rgb(172,124,0)",
			"rgb(0,184,0)",
			"rgb(0,168,0)",
			"rgb(0,168,68)",
			"rgb(0,136,136)",
			"rgb(0,0,0)",
			"rgb(0,0,0)",
			"rgb(0,0,0)",
			
			"rgb(248,248,248)",
			"rgb(60,188,252)",
			"rgb(104,136,252)",
			"rgb(152,120,248)",
			"rgb(248,120,248)",
			"rgb(248,88,152)",
			"rgb(248,120,88)",
			"rgb(252,160,68)",
			"rgb(248,184,0)",
			"rgb(184,248,24)",
			"rgb(88,216,84)",
			"rgb(88,248,152)",
			"rgb(0,232,216)",
			"rgb(120,120,120)",
			"rgb(0,0,0)",
			"rgb(0,0,0)",
			
			"rgb(252,252,252)",
			"rgb(164,228,252)",
			"rgb(184,184,248)",
			"rgb(216,184,248)",
			"rgb(248,184,248)",
			"rgb(248,164,192)",
			"rgb(240,208,176)",
			"rgb(252,224,168)",
			"rgb(248,216,120)",
			"rgb(216,248,120)",
			"rgb(184,248,184)",
			"rgb(184,248,216)",
			"rgb(0,252,252)",
			"rgb(216,216,216)",
			"rgb(0,0,0)",
			"rgb(0,0,0)"
		]
	}	
}

bhack.tv.canvas = $("#television")[0];
bhack.tv.fill("#FFF");

var x = BSim.Beta.Opcodes[0x00].exec;
BSim.Beta.Opcodes[0x00].exec = function PRIV_OP_MOD(a, literal, c) {
	switch(literal) {
		case 99:	// clear
			bhack.tv.clear();
			break;
		case 100:	// set pos
			bhack.tv.set_pos(this.readRegister(a));
			break;
		case 101:	// put byte
			bhack.tv.out(this.readRegister(a));
			break;
			
		default:
			x(a, literal, c);
	}
}

mario.uasm

.include "/shared/bsim/beta.uasm"          // include instruction macros

// TELEVISION
.macro TV_CLEAR() PRIV_OP (99)
.macro TV_POS() PRIV_OP (100)
.macro TV_OUT() PRIV_OP (101)

// MACROS
.macro DEC(R) SUBC(R, 1, R)
.macro INC(R) ADDC(R, 1, R)

// INTERRUPTS

. = VEC_RESET
	BR(int_reset)

// MAIN

. = 20

int_reset:
	BR(__start)

__start:
	LDR(stack_base, SP)	// setup stack
	
	// setup tv
	TV_CLEAR()
	
	BR(draw_mario, LP)	// draw our hero

__halt:	HALT()
	BR(__halt)

pixel_i = R6

line = R7
line_i = R8
line_ptr = R9

color = R10
color_i = R11
color_ptr = R12

draw_mario:
color_loop_init:
	CMOVE(0, color_i)
color_loop:
	// lookup color
	MOVE(color_i, R0)
	MULC(R0, 4, R0)
	ADDC(R0, mario_colors, R0)
	LD(R0, 0, color)
	
	// set bitmap pointer
	MULC(color_i, 16*4, color_ptr)
	ADDC(color_ptr, mario_bitmap, color_ptr)
	MOVE(color_ptr, line_ptr)
line_loop_init:
	CMOVE(0, line_i)
line_loop:
	// get line
	LD(line_ptr, 0, line)
	
	// if line is zero, skip it
	BEQ(line, line_loop_end, R31)
pixel_loop_init:
	CMOVE(0, pixel_i)
pixel_loop:
	// get pixel
	SHLC(line, 1, line)
	ANDC(line, 0x800, R0)
	SHRC(R0, 11, R0)
	BEQ(R0, pixel_alpha, R31)
pixel_colored:
	MOVE(color, R0)
	BR(pixel_out)
pixel_alpha:
	CMOVE(0, R0)
	SUBC(R0, 1, R0)
pixel_out:
	TV_OUT()
pixel_loop_end:
	INC(pixel_i)
	CMPEQC(pixel_i, 12, R0)
	BEQ(R0, pixel_loop)
line_loop_end:
	// go to next line in mem
	ADDC(line_ptr, 4, line_ptr)
	
	// put tv on next line
	SUB(line_ptr, color_ptr, R0)
	MULC(R0, 96/4, R0)
	TV_POS()
	
	INC(line_i)
	CMPEQC(line_i, 16, R0)
	BEQ(R0, line_loop)
color_loop_end:
	INC(color_i)
	CMPEQC(color_i, 3, R0)
	BEQ(R0, color_loop)
	
	RTN()
	
mario_colors:
	LONG(0x16)	// NES red
	LONG(0x09)	// NES green
	LONG(0x38)	// NES yellow

mario_bitmap:
mario_red:
	LONG(0x1f0)
	LONG(0x3fe)
	LONG(0x0)
	LONG(0x0)
	LONG(0x0)
	LONG(0x0)
	LONG(0x0)
	LONG(0x80)
	LONG(0x90)
	LONG(0xf0)
	LONG(0x168)
	LONG(0x1f8)
	LONG(0x3fc)
	LONG(0x39c)
	LONG(0x0)
	LONG(0x0)
  
mario_green:
	LONG(0x0)
	LONG(0x0)
	LONG(0x390)
	LONG(0x510)
	LONG(0x588)
	LONG(0x61e)
	LONG(0x0)
	LONG(0x370)
	LONG(0x76e)
	LONG(0xf0f)
	LONG(0x204)
	LONG(0x0)
	LONG(0x0)
	LONG(0x0)
	LONG(0x70e)
	LONG(0xf0f)

mario_yellow:
	LONG(0x0)
	LONG(0x0)
	LONG(0x68)
	LONG(0x2ee)
	LONG(0x277)
	LONG(0x1e0)
	LONG(0x1fc)
	LONG(0x0)
	LONG(0x0)
	LONG(0x0)
	LONG(0xc93)
	LONG(0xe07)
	LONG(0xc03)
	LONG(0x0)
	LONG(0x0)
	LONG(0x0)

stack_base:
    LONG(.+4)      // Pointer to bottom of stack
    . = .+0x1000   // Reserve space for stack