Power management is a crucial design consideration for mobile battery-operated systems. Frequency scaling and doze mode are two ways to manage CPU power. Each of these, used separately, reduces the power usage of the CPU, but something unexpected is observed when both are used together: no additional power savings is achieved. Doze mode is the simplest method of managing CPU power, and for the case of the i.MX21 processor, saves more power than frequency scaling. However, the CPU is not the only power consumer; the whole system needs to be considered in an effective power management design.