Struct Types
Structs are the basis building blocks for any e language based testbenches. This are similar to class in C++ and thus are used for constructing compound data structures. Like in C++ and C, we can use this compound data structures in all the places like
- Can be used as regular data types in any context where a type is required
- The default value for a struct is NULL
- Passing to/from methods (functions in C).
- Can be used in another stuct as normal data type
- You can also define a variable using a struct type.
| Example |
| . |
1 <'
2 struct data_types4 {
3 mem_addr : uint (bits : 8);
4 mem_data : uint (bytes: 1);
5 mem_rdwr : bit;
6 };
7 // Just to check our code
8 extend sys {
9 data : data_types4;
10
11 print_struct(pdata : data_types4) is {
12 outf ("Address : %d\n",pdata.mem_addr);
13 outf ("Data : %d\n",pdata.mem_data);
14 outf ("Read : %d\n",pdata.mem_rdwr);
15 };
16 run() is also {
17 out("Generating............");
18 gen data;
19 print_struct(data);
20 out("Generating............");
21 gen data;
22 print_struct(data);
23 out("Generating............");
24 gen data;
25 print_struct(data);
26 };
27 };
28 '>
Generating............
Address : 189
Data : 58
Read : 0
Generating............
Address : 120
Data : 148
Read : 1
Generating............
Address : 34
Data : 148
Read : 0
We will see more on the structs in next section.
List Types
List is same as that we find in TCL lanuage. List types hold ordered collections of data elements where each data element conforms to the same type. Items in a list can be indexed with the subscript operator [ ], by placing a non-negative integer expression in the brackets. List indexes start at zero. You can select an item from a list by specifying its index.
Lists are defined by using the list of keyword in a variable or a field definition.
Note :e does not support multi-dimensional lists (lists of lists). To create a list with sublists in it, you can create a struct to contain the sublists, and then create a list of such structs as the main list. The default value of a list is an empty list.
| There are two of lists in e language |
| . |
- Regular list
| ||
| List methods
Regular Lists The examples below is a regular list, Where we can access a item with []. Example 1 <' 2 type packet_protocol : [ETHERNET, IEEE, ATM]; 3 4 struct packet { 5 protocol : packet_protocol; 6 // payload is list of bytes 7 // Which size is always 10 bytes 8 payload : list of byte; 9 keep payload.size() == 10; 10 }; 11 // Just to check our code 12 extend sys { 13 // Create the list of the packets 14 data : list of packet; 15 // Set number of packets to generate to 4 16 // i.e. set the size of list 17 keep data.size() == 4; 18 run() is also { 19 gen data; 20 for each in data do { 21 print it; 22 print it.payload; 23 }; 24 }; 25 }; 26 '> it = packet-@0: packet ---------------------------------------------- @list_example 0 protocol: IEEE 1 payload: (10 items) it.payload = (10 items, dec): 133 185 157 142 231 104 85 230 102 168 .0 it = packet-@1: packet ---------------------------------------------- @list_example 0 protocol: ATM 1 payload: (10 items) it.payload = (10 items, dec): 2 44 224 216 156 14 216 12 52 80 .0 it = packet-@2: packet ---------------------------------------------- @list_example 0 protocol: ETHERNET 1 payload: (10 items) it.payload = (10 items, dec): 112 201 150 25 244 227 194 171 77 96 .0 it = packet-@3: packet ---------------------------------------------- @list_example 0 protocol: ETHERNET 1 payload: (10 items) it.payload = (10 items, dec): 69 214 58 191 194 192 64 252 143 82 .0 Keyed Lists A keyed list data type is similar to hash tables or association lists found in other programming languages. The declaration below specifies that memory is a list of byte, and that the addr filed is used as the hash key.
1 <' 2 struct base_object { 3 addr : byte; 4 data : byte; 5 }; 6 7 struct keyed_list { 8 ! memory : list (key:addr) of base_object; 9 // writing to a keyed list 10 write_item(object : base_object) is { 11 memory.add(object); 12 print object; 13 }; 14 // Reading from keyed list 15 read_item(object : base_object) is { 16 var local_object : base_object = memory.key(object.addr); 17 print local_object; 18 }; 19 }; 20 // Just to check our code 21 extend sys { 22 data : base_object; 23 mem_model : keyed_list; 24 run() is also { 25 gen data; 26 mem_model.write_item(data); 27 mem_model.read_item(data); 28 }; 29 }; 30 '> object = base_object-@0: base_object ---------------------------------------------- @keyed_list 0 addr: 116 1 data: 2 local_object = base_object-@0: base_object ---------------------------------------------- @keyed_list 0 addr: 116 1 data: 2 Keyed lists cannot be generated. Trying to generate a keyed list results in an error. Therefore, keyed lists must be defined with the do-not-generate sign. The only restriction on the type of the list elements is that they cannot themselves be lists String Type The predefined type string is the same as the C NULL terminated (zero terminated) string type. You can assign a series of ASCII characters enclosed by quotes (" ") to a variable or field of type string. |
Example
1 <'
2 extend sys {
3 // Declare a variable as string type
4 my_string : string;
5 run() is also {
6 my_string = "This is sample string";
7 print my_string;
8 };
9 };
10 '>
my_string = "This is sample string"
You cannot access bits or bit ranges of a string, but you can convert a string to a list of bytes and then access a portion of the string.
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