System Clock, Machine cycle, Instruction cycle and T-state
The higher system clock, machine cycle and instruction
cycle is used to measure the CPU/controller speed to execute/process the
program (firmware). The higher clock speed will indicate more instructions
processed per second. The Alternate measure of processing speed is the number
of instructions a CPU can process per second (instruction per second or IPS). This
unit is measure CPU/controller itself speed, is cannot indicate the whole system
performance and speed, because the system performance/speed may affect by
memory speed, bus speed, bus width (8 bits, 16bits, 32bits) and device that interface
with CPU/controller.
System Clock
System clock is main reference clock for whole system.
Normally, it is crystal clock at external. It measure in units Hertz(Hz)
T-state
T-state is sub step in machine cycle. It is one of the states
in machine cycle. Normally, each state will using single system clock.
Machine Cycle
Machine cycle is defined as the time required completing
the one operation. It includes of 3-6 T-state. Multiple sub process (T-state) combines
and become single machine cycle. The other word, multiple system clock needed
to execute single machine cycle. The sub process in machine cycle will have:-
Fetch = the program instruction is fetched to registry.
Decode = the instructions are decoded so that control
unit, ALU and FPU can understand the,
Execute = the instructions are carried out
Store = the original data or the result from the ALU or
FPU execution is stored either in the CPU registers or in memory, depending on
the instruction.
Today technology, there have some CPU/controller using
clock double up circuit to increase internal system clock. It will become the
CPU/controller need lower frequency system clock but can execute higher speed.
