energy-efficiency.md

Energy Efficiency

A guide to the various energy efficiency optimisations used by the core.

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Clock gating

Clock gating is used aggressivley to avoid clocking registers whos values do not need to change. The separate clock signals are listed below, along with the part of the core they are requested by.

Clock Signal	Usage
f_clk	Global free-running clock, used for in-core timers.
g_clk	Global gated clock, used by default in the core.
g_clk_rf	Register file gated clock.
g_clk_mul	Multiplier gated clock.

• The core level g_clk_* is derived from the f_clk.

• Each g_clk* clock signal has an associated *_req line:

  • When the *_req line is set, the clock must be delivered.

  • When the *_req line is low, the clock may be gated. The core cannot assume that just because *_req is low, the clock will not tick.

The g_clk signals are derived from f_clk:

             ----[Clk Gate]-----> g_clk
             |    ^
             |    |- g_clk_req
             |
             |
--> f_clk ---|---[Clk Gate]-----> g_clk_rf
             |    ^
             |    |- g_clk_rf_req
             |
             |
             ----[Clk Gate]-----> g_clk_mul
                  ^
                  |- g_clk_rf_req

Single Bit Sign Extension

• TBD

Glitch Minimisation

• TBD