SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
Figure 5-4 highlights the high level flow-chart for entry into any of the DSP powerdown modes. The system host (typically) first informs the DSP that it should enter a powerdown mode. The host (g.h. device MPU) sends a software message (normally via system level mailbox+interrupt). In parallel, the PRCM (via host or DSP programmation) will hardware assert an SIdleReq request to the DSP via the IDLE Protocol connection. At the next stage, the C66x CPU, in general, performs any software bookkeeping necessary to transition the DSP subsystem to a quiescent state. This may include : waiting for outstanding DMA transfers to complete, waiting for outstanding DMA transfers to complete, etc. The C66x processor should finally execute the IDLE instruction when it is ready to be powered-down. Assuming the DSP_SYS_SYSCONFIG[5:4] STANDBYMODE is enabled, then the hardware will transition to an idle state and notify to the system the intention to enter powerdown state to the system via the master standby and slave idle protocols. After IDLE and MSTANDBY handshake is completed, the DSP clocks are optionally gated; and supply rails are optionally reduced or turned off.
The PM_DSPx_PWRSTCTRL[1:0] POWERSTATE bit field in device PRCM must be set to 0x3 (ON state) prior to performing the sequence shown in Figure 5-4 for the transition to be successful.