L2 - Clocks Flashcards
What does accuracy denote in digital physical clocks?
maximum offset of a clock
Rate Correction
correct the rate of the clock
- analog: change parameters of the crystal oscillator
- digital: change number of microticks per macrotick
What is a microtick?
Microtick is a periodic event.
Events are _______________.
Events are partially ordered. Temporal order necessary but not as sufficient as casual order.
What’s the standard procedure for fault tolerant algorithms?
- Get state of global time counters & all other nodes
- Analysis
- Error Detection
- Calculate Correction Value
- Adjustment of local time counter
In which parts can the cluster model be divided?
- operator cluster (human operator)
- computational cluster (RTS)
- controlled cluster (physical plant or machine to be controlled)
State Correction
correct local time immediately
What does jitter depend on?
The jitter EPSILON depends on the system level of creation.
How do you describe the time between microticks and how it is mathematically defined?
The time between two microticks is a granule and defined by 1/frequency.
External Clock Synchronization
External Clock Synchronization links the global time of a system to an external time reference (e.g.: UTC). Important for GPS and high speed printing.
What is jitter?
Jitter (EPSILON) is the deviation from true periodicity and defines the precision of the synchronization. Jitter is a significant, and usually undesired, factor in the design of almost all communications links.
What min. precision should the synchronization have in the Application, the Kernel and the Hardware?
- Application: max 5ms
- Kernel: max. 100us
- Hardware: max. 1us
Name a characteristic of a perfect clock.
Drift rate RHO should be 0. Drift rate depends on temperature and ageing.
What does the drift offset GAMMA indicate?
The drift offset GAMMA indicates the maximum offset before synchronization.
