System Clock Description
MPC5510 Microcontroller Family Reference Manual, Rev. 1
Freescale Semiconductor
3-7
Preliminary
3.5.2
Halt Clock Gating
System clock gating is forced via the centralized halt mechanism. The SIU_HLT register’s bits
corresponding to individual modules are configured to determine which modules are clock gated.
The HLT bits are used to drive the stop inputs to the modules. After the module completes a clean
shutdown, the module asserts the stop acknowledge handshake. The stop acknowledge is visible in the
SIU_HLTACK read-only register bits. The modules are individually controlled and halted.
The halted module recovers when the HLT bit is cleared by software. After HLT is cleared, the device’s
logic will re-enable the clocks to the modules and negate the stop signal after the required timing has been
met.
There is no hardware disable for the eDMA and FlexRay modules. Thus before setting the HLT bits for
these masters, software should take actions to prepare for the eDMA and FlexRay clocks to be stopped.
Then software sets the HLT bits for the eDMA and FlexRay to indicate to the clock logic that the clocks
to these modules can now be stopped.
When the HLT bits for the eDMA and FlexRay are set and when the Z0 and Z1 have executed WAIT
instructions, then the clocks to the platform are also gated. The platform logic includes the MPU, AXBS,
AIPS, and MCM. The INTC and SIU are not clock gated to allow for an interrupt to be used to exit WAIT.
3.5.3
Core WAIT Clock Gating
Core clock gating is enabled via the CPU WAIT instruction (or, if the core is in reset, by the CRP Core
Reset bit).
The Z1 and Z0 cores may be idled by their WAIT instructions. The WAIT instructions are used as a
power-saving feature to halt the core. Executing the WAIT instruction puts the corresponding core in an
idle state at a clean transition point. When the core stops, clocks to the core are gated off, and the core
Table 3-2. Software-Controlled Clock Gating Support
Block Name
Register Name
Bit Name
DSPI
MCR
MDIS
ESCI
MCR
MDIS
FlexCAN
MCR
MDIS
EMIOS
MCR
MDIS
EBI
MCR
MDIS
MLB
MCR
MDIS
PIT_RTI
MCR
MDIS
1
1
Only the PIT timers are disabled by MDIS. The RTI is not affected by MDIS.
I
2
C
IBCR
MDIS
NPC
MCR
MCKO_EN, MCKO_GT
Flash Array
MCR
STOP