sv typedef struct packed用法
时间: 2023-06-29 15:05:45 浏览: 337
在SystemVerilog中,`typedef`用于定义一个新的数据类型,而`struct`则用于定义一个结构体。`packed`关键字用于指示编译器如何对结构体进行内存分配,它告诉编译器按照最小的字节数对结构体进行对齐,以减少内存占用。
因此,`typedef struct packed`可以用于定义一个新的紧凑型结构体,其语法如下:
```systemverilog
typedef struct packed {
// 结构体成员定义
} struct_name;
```
例如,以下代码定义了一个名为`my_struct`的结构体类型,该结构体包含三个成员,每个成员都是一个位向量类型,占用3个字节的内存空间:
```systemverilog
typedef struct packed {
logic [7:0] a;
logic [7:0] b;
logic [7:0] c;
} my_struct;
```
注意,在使用`packed`关键字时,需要确保结构体的所有成员都是位向量类型,因为对于非位向量类型,编译器可能会按照字节对齐方式进行内存分配。
相关问题
sv中typedef struct packed
typedef struct packed是C语言中的关键字组合,用于定义一个紧凑的结构体。
在C语言中,struct关键字用于定义结构体,而typedef关键字用于给类型起别名。packed是一个属性说明符,它告诉编译器将结构体按照紧凑的方式进行内存布局,不插入任何填充字节。
因此,typedef struct packed可以用来定义一个紧凑的结构体,并为该结构体类型起一个别名。这样,在后续的代码中,就可以直接使用这个别名来声明该类型的变量。
module test; typedef struct packed { logic [9:-1][2:0] a; } ST1; typedef struct { ST1 st1; packed ST1 st2[]; logic [7:0] b; } ST4; initial begin ST4 st4; st4.st1.a[0][0] = 1; for (int i = 0; i < 5; i++) begin st4.st2.push_back(ST1'(i + 1)); end st4.b = 8'hAA; $display("%s", st4.st2); //CHECK-001:'{a:'h1}, st2:'{'a:'h1}, '{a:'h0},'{a:h1}}} end endmodule this piece of system verilog code, when compiled by vcs, it reports 1 error: Parsing design file'sc_assignment_pattern_030.sv' Error-[SE] Syntax error Following verilog source has syntax error: "sc_asssignment_pattern_030.sv", 21: token is 'packed' packed ST1 st2[]; System Verilog keyword 'packed' is not expected to be used in this context. How should I fix this error so that it can be compiled successfully by vcs?
The error message indicates that the use of 'packed' in the typedef declaration of 'st2' is incorrect. The 'packed' keyword is used to specify that a structure or union should be packed tightly in memory, but it cannot be used in the context of an array declaration.
To fix this error, you can remove the 'packed' keyword from the typedef declaration of 'st2'. The corrected code should look like:
```
module test;
typedef struct packed {
logic [9:-1][2:0] a;
} ST1;
typedef struct {
ST1 st1;
ST1 st2[];
logic [7:0] b;
} ST4;
initial begin
ST4 st4;
st4.st1.a[0][0] = 1;
for (int i = 0; i < 5; i++) begin
st4.st2.push_back(ST1'(i + 1));
end
st4.b = 8'hAA;
$display("%s", st4.st2); //CHECK-001:'{a:'h1}, st2:'{'a:'h1}, {'a:'h0},{'a:h1}}}
end
endmodule
```
By removing the 'packed' keyword from the declaration of 'st2', the code should now compile without any syntax errors.
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