enum · struct · package

In Industry

Large RTL codebases live and die by their type systems. ARM's CPU projects have central package files defining instruction opcodes, cache states, pipeline bundle types — referenced by hundreds of modules. Intel's ASIC flows require typedef enum for every FSM state. Without these features, thousand-module codebases would drown in localparam and port lists. Shared types are how large teams stay sane.

In This Course

Your Week 4 capstone will have a handful of modules sharing state definitions. package lets you define them once. typedef enum lets the compiler type-check your FSM transitions. struct lets you bundle UART frame fields into one signal. Modest codebase, large effect.

// Bundle a UART frame into one struct
typedef struct packed {
    logic       start_bit;    // 1 bit
    logic [7:0] data;         // 8 bits
    logic       parity;       // 1 bit
    logic       stop_bit;     // 1 bit
} uart_frame_t;            // 11b packed L→R

// One signal, not four
uart_frame_t frame_in, frame_out;

// Field-level access:
assign frame_out.data = processed_byte;
// Or whole-struct literal:
assign frame_out = '{start_bit:0, data:8'hA5,
                     parity:1, stop_bit:1};

// File: uart_pkg.sv
package uart_pkg;
    parameter int DEFAULT_BAUD = 115200;

    typedef enum logic [1:0] {
        PARITY_NONE, PARITY_EVEN,
        PARITY_ODD,  PARITY_MARK
    } parity_t;

    typedef struct packed {
        logic       start_bit;
        logic [7:0] data;
        parity_t    parity_mode;   // nested!
        logic       stop_bit;
    } frame_t;
endpackage

// File: uart_tx.sv
import uart_pkg::*;        // frame_t, parity_t, DEFAULT_BAUD

module uart_tx #(parameter BAUD = DEFAULT_BAUD) (
    input frame_t frame_in,
    // ...
);