Cortex-A8 R2P2.pdf - ARM Information Center

Debug12.12 Debugging systems with energy management capabilitiesThe processor offers functionality for debugging systems with energy managementcapabilities. This section describes scenarios where the OS takes energy-savingmeasures when in an idle state.The different measures that the OS can take to save energy during an idle state aredivided into two groups:StandbyThe OS takes measures that reduce energy consumption but maintain theprocessor state.Power down The OS takes measures that reduce energy consumption but do notmaintain the processor state. Recovery involves a reset of the core afterthe power level has been restored, and reinstallation of the processorstate.12.12.1 StandbyStandby is the least invasive OS energy saving state because it only implies that the coreis unavailable. It does not clear any of the debug settings. For this case, ifDBGNOCLKSTOP is HIGH, the processor guarantees the following:• If the processor is in standby and a halting debug event occurs, the processor:— leaves standby— retires the Wait-For-Interrupt (WFI) instruction— enters debug state.• The processor responds to APB accesses as if it was not in standby.NoteIf you implement the CoreSight Debug Access Port (DAP) in your system, ARMrecommends that the DAP CDBGPWRUPREQ output is connected to theDBGNOCLKSTOP processor input.12.12.2 Emulating power downBy writing to bit [0] of the PRCR, the debugger asserts the DBGNOPWRDWN output.The expected usage model of this signal is that it is connected to the system powercontroller and that, when HIGH, it indicates that this controller can work in emulatemode.12-116 Copyright © 2006-2008 ARM Limited. All rights reserved. ARM DDI 0344E