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Migen and nMigen compatibility summary

nMigen intends to provide as close to 100% compatibility to Migen as possible without compromising its other goals. However, Migen widely uses * imports, tends to expose implementation details, and in general does not have a well-defined interface. This document attempts to elucidate a well-defined Migen API surface (including, when necessary, private items that have been used downstream), and describes the intended nMigen replacements and their implementation status.

API change legend:

  • id: identical
  • obs: removed or incompatibly changed with compatibility stub provided
  • obs →n: removed or incompatibly changed with compatibility stub provided, use n instead
  • brk: removed or incompatibly changed with no replacement provided
  • brk →n: removed or incompatibly changed with no replacement provided, use n instead
  • →n: renamed to n
  • ⇒m: merged into m
  • a=→b=: parameter a renamed to b
  • a=∼: parameter a removed
  • .a=→.b: attribute a renamed to b
  • .a=∼: attribute a removed
  • ?: no decision made yet

When describing renames or replacements, mod refers to a 3rd-party package mod (no nMigen implementation provided), .mod.item refers to nmigen.mod.item, and "(import .item)" means that, while item is provided under nmigen.mod.item, it is aliased to, and should be imported from a shorter path for readability.

Status legend:

  • (−) No decision yet, or no replacement implemented
  • (+) Implemented replacement (the API and/or compatibility shim are provided)
  • (⊕) Verified replacement and/or compatibility shim (the compatibility shim is manually reviewed and/or has 100% test coverage)
  • (⊙) No direct replacement or compatibility shim is provided

Compatibility summary

  • (−) fhdl → .hdl
    • (⊕) bitcontainer ⇒ .tools
      • (⊕) log2_int id
      • (⊕) bits_for id
      • (⊕) value_bits_sign → Value.shape
    • (⊕) conv_output obs
    • (⊕) decorators ⇒ .hdl.xfrm
      Note: transform_* methods not considered part of public API.
      • (⊙) ModuleTransformer brk
      • (⊙) ControlInserter brk
      • (⊕) CEInserter → EnableInserter
      • (⊕) ResetInserter id
      • (⊕) ClockDomainsRenamer → DomainRenamer, cd_remapping=→domain_map=
    • (⊙) edif brk
    • (⊕) module obs → .hdl.dsl
      Note: any class inheriting from Module in oMigen should inherit from Elaboratable in nMigen and use an nMigen Module in its .elaborate() method.
      • (⊕) FinalizeError obs
      • (⊕) Module obs → .hdl.dsl.Module
    • (⊙) namer brk
    • (⊙) simplify brk
    • (⊕) specials obs
      • (⊙) Special brk
      • (⊕) Tristate obs
      • (⊕) TSTriple obs → .lib.io.Pin
      • (⊕) Instance → .hdl.ir.Instance
      • (⊕) Memory id
        Note: nMigen memories should not be added as submodules.
        • (⊕) .get_port obs → .read_port() + .write_port()
      • (⊕) _MemoryPort obs → .hdl.mem.ReadPort + .hdl.mem.WritePort
      • (⊕) READ_FIRST/WRITE_FIRST obs
        Note: READ_FIRST corresponds to mem.read_port(transparent=False), and WRITE_FIRST to mem.read_port(transparent=True).
      • (⊙) NO_CHANGE brk
        Note: in designs using NO_CHANGE, replace it with logic implementing required semantics explicitly, or with a different mode.
    • (⊕) structure → .hdl.ast
      • (⊕) DUID id
      • (⊕) _Value → Value
        Note: values no longer valid as keys in dict and set; use ValueDict and ValueSet instead.
      • (⊕) wrap → Value.cast
      • (⊕) _Operator → Operator, op=→operator=, .op→.operator
      • (⊕) Mux id
      • (⊕) _Slice → Slice id
      • (⊕) _Part → Part id
      • (⊕) Cat id, .l→.parts
      • (⊕) Replicate → Repl, v=→value=, n=→count=, .v→.value, .n→.count
      • (⊕) Constant → Const, bits_sign=→shape=, .nbits→.width
      • (⊕) Signal id, bits_sign=→shape=, attr=→attrs=, name_override=∼, related=, variable=∼, .nbits→.width
      • (⊕) ClockSignal id, cd=→domain=, .cd→.domain
      • (⊕) ResetSignal id, cd=→domain=, .cd→.domain
      • (⊕) _Statement → Statement
      • (⊕) _Assign → Assign, l=→lhs=, r=→rhs=
      • (⊕) _check_statement obs → Statement.cast
      • (⊕) If obs → .hdl.dsl.Module.If
      • (⊕) Case obs → .hdl.dsl.Module.Switch
      • (⊕) _ArrayProxy → .hdl.ast.ArrayProxy, choices=→elems=, key=→index=
      • (⊕) Array id
      • (⊕) ClockDomain → .hdl.cd.ClockDomain
      • (⊙) _ClockDomainList brk
      • (⊙) SPECIAL_INPUT/SPECIAL_OUTPUT/SPECIAL_INOUT brk
      • (⊙) _Fragment brk → .hdl.ir.Fragment
    • (⊙) tools brk
      • (⊙) insert_resets brk → .hdl.xfrm.ResetInserter
      • (⊙) rename_clock_domain brk → .hdl.xfrm.DomainRenamer
    • (⊙) tracer brk
      • (⊕) get_var_name → .tracer.get_var_name
      • (⊙) remove_underscore brk
      • (⊙) get_obj_var_name brk
      • (⊙) index_id brk
      • (⊙) trace_back brk
    • (⊙) verilog
      • (⊙) DummyAttrTranslate ?
      • (⊕) convert obs → .back.verilog.convert
    • (⊙) visit brk → .hdl.xfrm
      • (⊙) NodeVisitor brk
      • (⊙) NodeTransformer brk → .hdl.xfrm.ValueTransformer/.hdl.xfrm.StatementTransformer
  • (−) genlib → .lib
    • (−) cdc ?
      • (⊙) MultiRegImpl brk
      • (⊕) MultiReg → .lib.cdc.FFSynchronizer
      • (−) PulseSynchronizer ?
      • (−) BusSynchronizer ?
      • (⊕) GrayCounter obs → .lib.coding.GrayEncoder
      • (⊕) GrayDecoder obs → .lib.coding.GrayDecoder
        Note: .lib.coding.GrayEncoder and .lib.coding.GrayDecoder are purely combinatorial.
      • (−) ElasticBuffer ?
      • (−) lcm ?
      • (−) Gearbox ?
    • (⊕) coding id
      • (⊕) Encoder id
      • (⊕) PriorityEncoder id
      • (⊕) Decoder id
      • (⊕) PriorityDecoder id
    • (−) divider ?
      • (−) Divider ?
    • (⊕) fifo → .lib.fifo
      • (⊕) _FIFOInterface → FIFOInterface
      • (⊕) SyncFIFO id, .replace=∼
      • (⊕) SyncFIFOBuffered id, .fifo=∼
      • (⊕) AsyncFIFO ?
      • (⊕) AsyncFIFOBuffered, .fifo=∼
    • (⊕) fsm obs
      Note: FSMs are a part of core nMigen DSL; however, not all functionality is provided. The compatibility shim is a complete port of Migen FSM module.
    • (⊙) io brk
      Note: all functionality in this module is a part of nMigen platform system.
    • (−) misc ?
      • (−) split ?
      • (−) displacer ?
      • (−) chooser ?
      • (−) timeline ?
      • (−) WaitTimer ?
      • (−) BitSlip ?
    • (⊕) record obs → .hdl.rec.Record
      Note: nMigen uses a Layout object to represent record layouts.
      • (⊕) DIR_NONE id
      • (⊕) DIR_M_TO_S → DIR_FANOUT
      • (⊕) DIR_S_TO_M → DIR_FANIN
      • (⊕) Record id
      • (⊙) set_layout_parameters brk
      • (⊙) layout_len brk
      • (⊙) layout_get brk
      • (⊙) layout_partial brk
    • (⊕) resetsync obs
      • (⊕) AsyncResetSynchronizer obs → .lib.cdc.ResetSynchronizer
    • (−) roundrobin ?
      • (−) SP_WITHDRAW/SP_CE ?
      • (−) RoundRobin ?
    • (−) sort ?
      • (−) BitonicSort ?
  • (⊕) sim obs → .back.pysim
    Note: only items directly under nmigen.compat.sim, not submodules, are provided.
    • (⊙) core brk
    • (⊙) vcd brk → vcd
    • (⊙) Simulator brk
    • (⊕) run_simulation obs → .back.pysim.Simulator
    • (⊕) passive obs → .hdl.ast.Passive
  • (⊙) build brk
    Note: the build system has been completely redesigned in nMigen.
  • (⊙) util brk