dave_marsden wrote on Wednesday, August 27, 2008:
There is a distinction between power down, brown out and LPM0 through LPM3. LPM0 through LPM3 do not cause the processor to restart, but rather allow for resumption of execution with the CPU context intact. To the execution unit time appears to have stopped. The actual low power mode determines which internal clocks remain active. If the internal timers are configured to a clock source which remains active in the low power mode, then there is no need to compensate for the interval that the CPU was in the low power state. This also allows the OS’s tick timer to wake up the system at the same tick interval regardless of low power or full speed operation.
It is quite normal for a battery powered MSP430 system to enter the power down mode as quickly as practical and resume equally promptly. Normally the idle task defines to the system what should occur if no task require servicing. In a battery powered system, the thing to do when idle is conserve energy and to be ready to resume activity as efficiently (time and energy) as possible.
Performing system power up initialization would be extremely energy inefficient if it occurred every few milliseconds, hence the requirement to have the system enter a low power mode immediately in the event of no other actions required, to wait until the next clock tick or other system relevant event before resuming execution.