nv_rd16i2cr
return nv_rd16i2cr(i2c, addr, 0x0) >= 0;
return nv_rd16i2cr(i2c, addr, 0xff) == 0x3220 &&
nv_rd16i2cr(i2c, addr, 0xfe) == 0x5449;
int vshunt = nv_rd16i2cr(i2c, addr, shunt_reg);
int vbus = nv_rd16i2cr(i2c, addr, bus_reg);