Quartus® Prime Pro Edition User Guide: Platform Designer

ID 683609
Date 4/01/2024
Public

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4.8.3. Reducing Power Consumption by Disabling Logic

There are typically two types of low power modes: volatile and non-volatile. A volatile low power mode holds the component in a reset state. When the logic is reactivated, the previous operational state is lost. A non-volatile low power mode restores the previous operational state. You can use either software-controlled or hardware-controlled sleep modes to disable a component in order to reduce power consumption.

Software-Controlled Sleep Mode

To design a component that supports software-controlled sleep mode, create a single memory-mapped location that enables and disables logic by writing a zero or one. You can use the register’s output as a clock enable or reset, depending on whether the component has non-volatile requirements. The agent interface must remain active during sleep mode so that the enable bit is set when the component needs to be activated.

If multiple hosts can access a component that supports sleep mode, you can use the Mutex Intel® FPGA IP to provide mutually exclusive accesses to your component. You can also build in the logic to re-enable the component on the very first access by any host in your system. If the component requires multiple clock cycles to re-activate, then it must assert a wait request to prolong the transfer as it exits sleep mode.

Hardware-Controlled Sleep Mode

Alternatively, you can implement a timer in your component that automatically causes the component to enter a sleep mode based on a timeout value specified in clock cycles between read or write accesses. Each access resets the timer to the timeout value. Each cycle with no accesses decrements the timeout value by one. If the counter reaches zero, the hardware enters sleep mode until the next access.

Figure 181. Hardware-Controlled Sleep Components


This example provides a schematic for the hardware-controlled sleep mode. If restoring the component to an active state takes a long time, use a long timeout value so that the component is not continuously entering and exiting sleep mode. The agent interface must remain functional while the rest of the component is in sleep mode. When the component exits sleep mode, the component must assert the waitrequest signal until it is ready for read or write accesses.