System Idle Request - Texas Instruments OMAP5912 Reference Manual

System DMA

System IDLE Request

60 Direct Memory Access (DMA) Support
All internal clocks are in idle mode, disabled, when the following is fulfilled:
1) Clock_Autogating_on = 1 in DMA_GCR.
2) No nonsynchronized LChs are enabled.
3) Either no synchronized LChs are enabled, or synchronized LChs are
enabled but no DMA request is received or pending.
The system DMA wakes up if software enables a new LCh or if a DMA request
is received. The system DMA also wakes up temporarily if the MPU or OCP-I
wants to read or write to any of the registers.
The system DMA can be put into IDLE mode, when system needs to go into
power saving mode. See Multimedia Processor OMAP3.2 Subsystem
Reference Guide (SPRU749) and Multimedia Processor Power Management
Reference Guide (SPRU753) for more information on prerequisite steps to put
the system and/or the system DMA in idle. An idle request signal is sent to the
DMA when the system wants it to go idle.
As soon as the DMA detects an idle request, it enters idle mode when all PChs
are free (including PCh-D). All nonsynchronized LChs, synchronized LChs
without DMA request detected, and suspended LChs are unscheduled PChs.
The DMA enters idle mode even if one of the LCD controllers is assigned
PCh-D but is in sleep mode. The DMA temporarily wakes up if:
A synchronized LChs DMA request is detected
-
There are any writes to generic LCh registers
-
Any of the LCD controllers gets active
-
The DMA goes back to idle mode when all these tasks are completed. This
also means as long as the system is requesting the system DMA to be in idle,
nonsynchronized LChs can be enabled, but they are never activated.
Synchronized LChs can be enabled and hence, activated at DMA request
during this time.
The DMA finishes pending accesses of physical channels and resumes the
logical channel transfer when released from idle. Therefore, it is the
responsibility of software to ensure that when software issues IDLE
instruction, all logical channels have been serviced.
The power-saving difference between the dynamic idle mode and the system
idle request is provided by the clock tree between the clock generation module
and the system DMA clock input.
SPRU755B