The instruction fetch address phase is best thought of as residing in stage `X`. The 2-cycle feedback loop between jump/branch decode into address issue in stage `X`, and the fetch data phase in stage `F`, is what defines Hazard3's jump/branch performance.
Hazard3 implements either one or two AHB5 bus master ports. The single-port configuration is used when ease of integration is a priority, since it supports simpler bus topologies. The dual-port configuration adds a dedicated port for instruction fetch, which improves both the maximum frequency and the clock-for-clock performance.
Hazard3 uses AHB5 specifically, rather than older versions of the AHB standard, because of its support for global exclusives. This is a bus feature that allows a processor to perform an ordered read-modify-write sequence with a guarantee that no other processor has written to the same address range in between. Hazard3 uses this to implement multiprocessor support for the A (atomics) extension.
For minimal M-extension support, Hazard3 instantiates a sequential multiply/divide circuit (restoring divide, naive repeated-addition multiply). Instructions stall in stage `X` until the multiply/divide completes. Optionally, the circuit can be unrolled by a small factor to produce multiple bits ber clock -- 2 or 4 is achievable in practice.
A single-cycle multiplier can be instantiated, retiring either to stage 3 or stage 2 (configurable). By default only 32-bit `mul` is supported, which is by far the most common of the four multiply instructions.
