67 lines
2.0 KiB
Markdown
67 lines
2.0 KiB
Markdown
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# Virtual interfaces (Tier A #3)
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Status: **partial** — enough for basic UVM-agent style connectivity.
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## Supported in this slice
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```systemverilog
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interface bus_if;
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logic clk;
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logic [7:0] data;
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endinterface
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class driver;
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virtual interface bus_if vif; // class property
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function new(virtual interface bus_if i); // TF argument
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vif = i; // assign interface instance
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endfunction
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task drive(logic [7:0] d);
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@(posedge vif.clk); // edge wait via VI
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vif.data = d; // member write
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endtask
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endclass
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module top;
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bus_if bif();
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driver drv;
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initial begin
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drv = new(bif);
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// ...
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end
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endmodule
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```
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Also: member reads (`v = vif.data`) and anyedge / negedge waits on VI members.
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**Syntax note:** the type must be written as `virtual interface <name>`. Bare `virtual bus_if` is deferred (parser conflicts with `virtual class` / `virtual function`).
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## Encoding
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| Layer | Role |
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|-------|------|
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| Parse | `K_virtual_interface` + `virtual_interface_type_t` (class props / TF ports) |
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| Netlist | `netvif_t` (`IVL_VT_CLASS` so object load/store reuse works) |
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| Elab | `$ivl_vif_new` / `$ivl_vif_get` / `$ivl_vif_wait`; VI member lvals |
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| Runtime | `vvp_vif` + `%new/vif`, `%vif/load/vec4`, `%vif/store/vec4`, `%vif/wait` |
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A virtual interface is a handle to an interface instance: member access and waits go through the bound signals.
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## Example
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[`examples/virtual_interface/vif_basic.sv`](../examples/virtual_interface/vif_basic.sv) — prints `PASSED`.
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```bash
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./install/bin/iverilog -g2012 -o /tmp/vif_basic.vvp examples/virtual_interface/vif_basic.sv
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./install/bin/vvp /tmp/vif_basic.vvp
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```
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## Deferred (do not claim)
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- Bare `virtual bus_if` (without the `interface` keyword)
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- Virtual interface arrays
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- Modport-qualified virtual interfaces (type enforcement)
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- Clocking blocks on VI (Tier A #4)
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- Parameterized interfaces
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See also [STATUS.md](STATUS.md) and [ROADMAP.md](ROADMAP.md).
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