Chapter 2. The processor
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Figure 2.2: Addition between the two 32bit words
Figure 2.3: Addition between the four 16bit
Figure 2.4: Addition between the 8 8bit words
2.1.3
Predication
All the instructions in PLX are predicated. This means that every instruction has a
flag bit attached, if this bit is one then the instruction is executed else it is not. This
results in the processor not having branch instructions or branch hazards. All of the
instructions are propagated through the pipeline and those that have a zero predicate
flag are simply not executed. There are eight 1-bit predicate registers, numbered P0 to
P7. There are 16 of there 1byte predicate registers forming the predicate file. At any
given time only one register is active which is chosen by software. P0 is hardwired to 1
meaning that all instructions assigned to this predicate register will be executed.