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The IBM System/360 Model 91 was an early machine that supported out-of-order execution of instructions; it used the Tomasulo algorithm, which uses register renaming. The POWER1 from 1990 is the first microprocessor that used register renaming and out-of-order execution. This processor implemented register renaming only for floating-point loads.
Tomasulo's algorithm uses register renaming to correctly perform out-of-order execution. All general-purpose and reservation station registers hold either a real value or a placeholder value. If a real value is unavailable to a destination register during the issue stage, a placeholder value is initially used.
This same technique is used in the R10000 register renaming mapping file, which stores a 6-bit virtual register number for each of the physical registers. In the renaming file, the renaming state is checkpointed whenever a branch is taken, so that when a branch is detected to be mispredicted, the old renaming state can be recovered in a single ...
System Verilog is the first major HDL to offer object orientation and garbage collection. Using the proper subset of hardware description language, a program called a synthesizer, or logic synthesis tool , can infer hardware logic operations from the language statements and produce an equivalent netlist of generic hardware primitives [ jargon ...
the Tomasulo algorithm, which uses register renaming, allowing continual issuing of instructions The task of removing data dependencies can be delegated to the compiler, which can fill in an appropriate number of NOP instructions between dependent instructions to ensure correct operation, or re-order instructions where possible.
While process advances will allow ever greater numbers of execution units (e.g. ALUs), the burden of checking instruction dependencies grows rapidly, as does the complexity of register renaming circuitry to mitigate some dependencies. Collectively the power consumption, complexity and gate delay costs limit the achievable superscalar speedup.
High-level synthesis (HLS), sometimes referred to as C synthesis, electronic system-level (ESL) synthesis, algorithmic synthesis, or behavioral synthesis, is an automated design process that takes an abstract behavioral specification of a digital system and finds a register-transfer level structure that realizes the given behavior.
In computing, a linear-feedback shift register (LFSR) is a shift register whose input bit is a linear function of its previous state. The most commonly used linear function of single bits is exclusive-or (XOR). Thus, an LFSR is most often a shift register whose input bit is driven by the XOR of some bits of the overall shift register value.