SystemVerilog Struct
Table of Contents
The SystemVerilog struct groups the data types of multiple types. The entire group can be referenced as a whole, or the individual data type can be referenced by name.
Struct Syntax
Struct is defined with the Struct keyword followed by variables of multiple data type with in the curly braces.
typedef struct packed {
type_1 var_1;
type_2 var_2;
type_3 var_3;
} struct_name;
SystemVerilog Packed Struct
Struct defined with the keyword Packed is referred as packed struct
Only packed data types and integer data types are allowed with in the packed struct
Packed Struct example
In the below example, variable of bit type are grouped in the struct.
module struct_tb;
typedef struct packed {
bit [7:0] addr;
bit valid;
bit [31:0] data;
} mem_pkt;
mem_pkt pkt;
initial begin
// Initializing Struct
pkt = '{8'h6, 1'b1, 32'hC001_0FAB};
$display ("pkt = %p", pkt);
// Change the struct field value
pkt.addr = 8'h8;
$display ("pkt = %p", pkt);
// Change the struct field value
pkt.data = 32'hFFF0_0FFF;
$display ("pkt = %p", pkt);
end
endmodule
Simulator Output
pkt = '{addr:'h6, valid:'h1, data:'hc0010fab}
pkt = '{addr:'h8, valid:'h1, data:'hc0010fab}
pkt = '{addr:'h8, valid:'h1, data:'hfff00fff}
SystemVerilog UnPacked Struct
By default struct is of Unpacked type, i.e struct without Packed keyword.
Packed Struct example
In the below example, byte, enum and bit types are grouped in the struct.
module struct_tb;
typedef enum logic {INVALID_PKT,VALID_PKT} pkt_type;
typedef struct packed {
byte addr;
pkt_type valid;
bit [31:0] data;
} mem_pkt;
mem_pkt pkt;
initial begin
// Initializing Struct
pkt = '{8'h6, VALID_PKT, 32'hC001_0FAB};
$display ("pkt = %p", pkt);
// Change the struct field value
pkt.addr = 8'h8;
$display ("pkt = %p", pkt);
// Change the struct field value
pkt.valid = INVALID_PKT;
$display ("pkt = %p", pkt);
end
endmodule
Simulator Output
pkt = '{addr:'h6, valid:VALID_PKT, data:'hc0010fab}
pkt = '{addr:'h8, valid:VALID_PKT, data:'hc0010fab}
pkt = '{addr:'h8, valid:INVALID_PKT, data:'hc0010fab}