Button press:
0x08 a1 07 xx xx xx xx xx xx

0x08 = number of bytes following
0xA107 = keypress event

remaning 6 buttons are placeholders for pressed
keys. 0xFE means no key, other value indicates that
a key is pressed

xx: 00 = a, 01 = b, 02 = c, 03 = d, 0xFE = none


Joystick move:
0x05 a1 08 00 xx yy

xx = 0x7f = right, 0x80 = left
yy = 0x7f = down, 0x80 = up

left/down goes from 0x00 to 0x7f
right/up goes from 0x7f to 0x80