6.4.1 Embedded Power Controller
The EPC is composed of three main modules:
- An event arbitration module used to prioritize ON, OFF, WAKE, and SLEEP requests.
- A power state-machine used to determine which power sequence to execute, based on the system state (supplies, temperature, and so forth) and requested transition (from the event arbitration module).
- A power sequencer that fetches the selected power sequence from OTP and executes it. The power sequencer sets up and controls all resources accordingly, based on the definition of each sequence.
Figure 6-17 shows the EPC block diagram.
Figure 6-17 EPC Block Diagram
The power state-machine is defined through the following states:
- NO SUPPLY: The device is not powered by any energy source on the system power rail (VCC1 < POR).
- BACKUP: The device is not powered by a valid supply on the system power rail (VCC1 < VSYS_LO) (VCC > POR).
- OFF: The device is powered by a valid supply on the system power rail (VCC1 > VSYS_LO) and it is waiting for a start-up event or condition. All device resources are in the OFF state. The approximate time for device to arrive the OFF state from the NO SUPPLY state, without considering the rise time of VSYS and the settling time of the VSYS_LO comparator, is approximately 5.5 ms.
- ACTIVE: The device is powered by a valid supply on the system power rail (VCC1 > VSYS_LO) and has received a start-up event. It has switched to the ACTIVE state, having full capacity to supply the processor and other platform modules.
- SLEEP: The device is powered by a valid supply on the system power rail (VCC1 > VSYS_LO) and is in low-power mode. All configured resources are set to their low-power mode, which can be ON, SLEEP, or OFF depending on the specific resource setting. If a given resource is maintained active (ON) during low-power mode, then all its linked subsystems are automatically maintained active.
Figure 6-18 shows the state diagram for the power control state-machine.
Figure 6-18 State Diagram for the Power Control State-Machine
Power sequences define how a resource state switches between the OFF, ACTIVE, and SLEEP states, but they have no effect during the NO SUPPLY or BACKUP states. The EPC supervises the system according to these power sequences, once the device is brought into the OFF state from a NO SUPPLY or BACKUP state. This is achieved automatically by internal hardware controlling the device before handing it over to the EPC.
The allowed power transitions are:
- OFF to ACTIVE (OFF2ACT)
- ACTIVE to OFF (ACT2OFF)
- ACTIVE to SLEEP (ACT2SLP)
- SLEEP to ACTIVE (SLP2ACT)
- SLEEP to OFF (SLP2OFF)
Each power transition consists of a sequence of one or several register accesses that controls the resources according to the EPC supervision. Because these sequences are stored in nonvolatile memory (OTP), they cannot be altered.