function _init()
 local bgm=build_bgm()
 local free_patterns={}
 for i=0,63 do add(free_patterns,i) end

 bgm:build(free_patterns,0)

 cstore(0x3100,0x3100,0x1200)
 music(0)
end
function _update()
end
function _draw()
 cls(0)
 print("enjoy the music!")
end

function build_bgm()
 local bgm=song:new()

 bgm:add(32)

 local root=0
 for chan=0,7 do
  local p=root+chan*7
  local start=0+chan*1
  local v=5-chan/3
  local c=chan%4
  bgm:plot(c,start+0,{v=v,p=p})
  bgm:plot(c,start+1,{v=v,p=p+12})
  bgm:plot(c,start+2,{v=v,p=p+7,e=5})
  bgm:plot(c,start+3,{v=v-1,p=p+3,e=2})
  -- bgm:plot(c,start+4,{v=v-1,p=p})
 end

 return bgm
end