[UVM]UVM Sequence item

                               UVM Sequence item

       The sequence-item is written by extending the uvm_sequence_item, uvm_sequence_item inherits from the uvm_object via the uvm_transaction class. therefore uvm_sequence_item is of an object type.

       Before moving to uvm_sequence_item will look into uvm_object concepts required to write uvm_sequence_item, The uvm_object has a number of virtual methods that are used to implement common data object functions (copy, clone, compare, print, transaction, and recording) and these should be implemented to make the sequence_item more general purpose.also, uvm_object has macros defined in it, mainly Utility Macros and Field Macros.

一、UVM Utility Macros

       The utility macros provide implementations of the create method (needed for cloning) and the get_type_name method (needed for debugging), etc.

1、objects with no field macros,

`uvm_object_utils(TYPE)

2、objects with field macros,

`uvm_object_utils_begin(TYPE)
    `uvm_field_*(FIELD, FLAG)
`uvm_object_utils_end

二、UVM Field Macros

       The `uvm_field_* macros are invoked inside of the `uvm_*_utils_begin and `uvm_*_utils_end, for the implementations of the methods: copy, compare, pack, unpack, record, print, and etc.

       Each `uvm_field_* macro is named to correspond to a particular data type: integrals, strings, objects, queues, enum, etc., and each has at least two arguments: FIELD and FLAG.

`uvm_field_*(FIELD, FLAG);

FLAG	Description
UVM_ALL_ON	Set all operations on (default)
UVM_DEFAULT	Use the default flag settings
UVM_NOCOPY	Do not copy this field
UVM_NOCOMPARE	Do not compare this field
UVM_NOPRINT	Do not print this field
UVM_NODEFPRINT	Do not print the field if it is the same as its
UVM_NOPACK	Do not pack or unpack this field
UVM_PHYSICAL	Treat as a physical field. Use physical setting in policy class for this field
UVM_ABSTRACT	Treat as an abstract field. Use the abstract setting in the policy class for this field
UVM_READONLY	Do not allow the setting of this field from the set_*_local methods
A radix for printing and recording can be specified by OR’ing one of the following constants in the FLAG argument
UVM_BIN	Print/record the field in binary (base-2)
UVM_DEC	Print/record the field in decimal (base-10)
UVM_UNSIGNED	Print/record the field in unsigned decimal (base-10)
UVM_OCT	Print/record the field in octal (base-8).
UVM_HEX	Print/record the field in hexadecimal (base-16)
UVM_STRING	Print/record the field in string format
UVM_TIME	Print/record the field in time format

1、Sequence item:

       The sequence-item consist of data fields required for generating the stimulus.In order to generate the stimulus, the sequence items are randomized in sequences. Therefore data properties in sequence items should generally be declared as rand and can have constraints defined.Data fields represent the following types of information,

• Control Information  – a type of transfer, transfer size, etc
• Payload Information  –  data content of the transfer
• Configuration Information – mode of operation, error behavior, etc
• Analysis Information – fields used to capture information from DUT, ex: read data, response, etc

       As analysis information fields will be used for capturing response, except these fields the other fields can be declared as rand and can have constraints associated with it.

2、Sequence item example

class mem_seq_item extends uvm_sequence_item;
  //Control Information
  rand bit [3:0] addr;
  rand bit       wr_en;
  rand bit       rd_en;
   
  //Payload Information
  rand bit [7:0] wdata;
   
  //Analysis Information
       bit [7:0] rdata;
     
  //Utility and Field macros,
  `uvm_object_utils_begin(mem_seq_item)
    `uvm_field_int(addr,UVM_ALL_ON)
    `uvm_field_int(wr_en,UVM_ALL_ON)
    `uvm_field_int(rd_en,UVM_ALL_ON)
    `uvm_field_int(wdata,UVM_ALL_ON)
  `uvm_object_utils_end
   
  //Constructor
  function new(string name = "mem_seq_item");
    super.new(name);
  endfunction
   
  //constaint, to generate any one among write and read
  constraint wr_rd_c { 
    wr_en != rd_en; 
  };
   
endclass