The e language has a number of predefined data types including the integer and Boolean scalar types common to most programming languages. Below is list of data types that we will be seeing in detail in next few pages. As such e language data types are far better then what we find in SystemC and TestBuilder (man I hate type conversions).

• Scalar Types
• Scalar Subtypes
• Enumerated Scalar Types
• Struct Types
• Struct Subtypes
• List Types
• The String Type

Scalar data types are one of the below

• Numeric
• Boolean
• Enumerated

Numeric and Boolean Scalar Types

Below Table shows the e Numeric and Boolean scalar types

Example

  1 <'
  2 struct data_types1 {
  3   // Signed Integer Date Type
  4   memory_address : int; 
  5   // Unsigned Integer Data Type
  6   memory_data    : uint;
  7   // Bit Data Type
  8   chip_enable    : bit;
  9   // Byte Data Type
 10   read_data      : byte;
 11   // Time Data Type
 12   current_time   : time;
 13   // Boolean Data Type
 14 };
 15 '>

You can create a scalar subtype by using a scalar modifier to specify the range or bit width of a scalar type. You can also specify a name for the scalar subtype if you plan to use it repeatedly in your program. Unbounded integers are a predefined scalar subtype.

• int [0..100] (bits: 7)
• int [0..100] (bits: 7)
• int (bytes: 1)
• int (bits: 8)

Example

  1 <'
  2 
  3 type valid_range_a : int [0..100] (bits:8);
  4 type valid_range_d : int [0..150] (bytes:1);
  5 
  6 struct data_types2 {
  7   // Signed Integer Date Type
  8   memory_address : int (bits:8); 
  9   // Unsigned Integer Data Type
 10   memory_data    : uint (bits:8);
 11   // Valid range with bits
 12   read_address   : valid_range_a;
 13   // Valid range with byte
 14   read_data      : valid_range_d; 
 15 };
 16 '>

As in any programming language, we can have enumerated data types in e language also, Below is the list of things for a e language enumerated scalar types.

• You can define the valid values for a variable or field as a list of symbolic constants.
• These symbolic constants have associated unsigned integer values.
• By default, the first name in the list is assigned the value zero.
• Subsequent names are assigned values based upon the maximum value of the previously defined enumerated items + 1.
• You can also assign explicit unsigned integer values to the symbolic constants.
• We can define named enumerated type as an empty type, This can be later extended.

Example

  1 <'
  2 type   kind_default_values  : [good, bad];
  3 type   kind_assigned_values : [good = 2, bad = 3];
  4 type   kind_only_few        : [good = 3, bad];
  5 // Empty 
  6 type   packet_protocol: [];
  7 // Extend
  8 extend packet_protocol : [Ethernet, IEEE, foreign];
  9 //Sized 
 10 type   packet_kind: [good, bad] (bits: 2);
 11 
 12 struct data_types3 {
 13   packet_type  :  packet_protocol;
 14   packet_valid :  packet_kind;
 15 };
 16 // Just to check our code
 17 extend sys {
 18   data : data_types3;
 19   run() is also {
 20     gen data;
 21     print data;
 22     gen data;
 23     print data;
 24     gen data;
 25     print data;
 26   };
 27 };
 28 '>

  data = data_types3-@0: data_types3
	----------------------------------------------	@data_types3
0	packet_type:                    foreign
1	packet_valid:                   good
  data = data_types3-@1: data_types3
	----------------------------------------------	@data_types3
0	packet_type:                    foreign
1	packet_valid:                   bad
  data = data_types3-@2: data_types3
	----------------------------------------------	@data_types3
0	packet_type:                    Ethernet
1	packet_valid:                   good

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 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
• Keyed list

There are many default methods provided by e language to work with list data types. Some of them are listed below

• size() : This is used to set the size of the list.
• add() : Add an item to the end of a list
• add0() : Add an item to the head of a list
• clear(): Delete all items from a list
• delete() : Delete an item from a list
• insert(index,item) : Insert an item in a list at a specified index
• pop() : Remove and return the last list item
• pop0() : Remove and return the first list item
• push() : Add an item to the end of a list
• push0() : Add an item to the head of a list
• resize() : Change the size of a list
• key():Get the item that has a particular key
• key_index():Get the index of an item that has a particular key
• key_exists():Check that a particular key is in a list

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	

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.

Example

  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

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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