TC1796
System Units (Vol. 1 of 2)
System Control Unit
User’s Manual
5-5
V2.0, 2007-07
SCU, V2.0
5.1.3
Power Management Modes
This section describes in more detail the power management modes, their operations,
and how power management modes are entered and exited. It also describes the
behavior of TC1796 system components in all power management modes.
5.1.3.1
Idle Mode
The Idle Mode is requested by software when writing to register PMG_CSR with bit field
REQSLP = 01
B
. After requesting the Idle Mode, the power management state machine
posts an idle request signal to the CPU. The CPU finishes its current operation, sends
an acknowledge signal back to the PMSM, and then enters an inactive state in which the
CPU clocks and the DMI and PMI memory units are shut off.
Other system components that are able to write to register PMG_CSR can also request
the Idle Mode. For example, the PCP or DMA controller can request Idle Mode by writing
to the PMG_CSR register.
During Idle Mode, memory accesses to the DMI and PMI via the local memory buses
(DLMB and PLMB) cause these units to awaken automatically to handle the
transactions. When memory transactions are complete, the DMI and PMI return to Idle
Mode again.
The system will return to Run Mode through the occurrence of any of the following
conditions:
•
An interrupt signal is received from an enabled interrupt source.
•
A NMI request is received either from an external source via the NMI pin, or from the
Watchdog Timer. The Watchdog Timer triggers an NMI trap request in Idle Mode
when its count value (WDT_SR.WDTTIM) changes from 7FFF
H
to 8000
H
.
•
An external power-on reset signal (PORST), or hardware reset signal (HDRST) is
received.
•
A software reset is requested by a FPI Bus agent by writing to the reset request
register RST_REQ.
If any of these conditions arise, the TC1796 immediately awakens and returns to Run
Mode. If it is awakened by a hardware or software reset signal, the TC1796 system
begins its reset sequence. If it is awakened by a Watchdog Timer overflow event, it
executes the instruction following the one that was last executed before Idle Mode was
entered. If it is awakened by an NMI signal or interrupt signal, the CPU will immediately
vector to the appropriate handler.