What is an Interface ?
An Interface is a way to encapsulate signals into a block. All related signals are grouped together to form an interface block so that the same interface can be re-used for other projects. Also it becomes easier to connect with the DUT and other verification components.
Example
APB bus protocol signals are put together in the given interface. Note that signals are declared within interface and endinterface.
interface apb_if (input pclk);
logic [31:0] paddr;
logic [31:0] pwdata;
logic [31:0] prdata;
logic penable;
logic pwrite;
logic psel;
endinterface
Why are signals declared logic ?
logic is a new data type that lets you drive signals of this type via assign statements and in a procedural block. Remember that in verilog, you could drive a reg only in procedural block and a wire only in assign statement. But this is only one reason.
Signals connected to the DUT should support 4-states so that X/Z values can be caught. If these signals were bit then the X/Z would have shown up as 0, and you would have missed that DUT had a X/Z value.
break
module tb;
initial begin
// This for loop increments i from 0 to 9 and exit
for (int i = 0 ; i < 10; i++) begin
$display ("Iteration [%0d]", i);
// Let's create a condition such that the
// for loop exits when i becomes 7
if (i == 7)
break;
end
end
endmodule
Simulation Log ncsim> run Iteration [0] Iteration [1] Iteration [2] Iteration [3] Iteration [4] Iteration [5] Iteration [6] Iteration [7] ncsim: *W,RNQUIE: Simulation is complete.
continue
module tb;
initial begin
// This for loop increments i from 0 to 9 and exit
for (int i = 0 ; i < 10; i++) begin
// Let's create a condition such that the
// for loop
if (i == 7)
continue;
$display ("Iteration [%0d]", i);
end
end
endmodule
Simulation Log ncsim> run Iteration [0] Iteration [1] Iteration [2] Iteration [3] Iteration [4] Iteration [5] Iteration [6] Iteration [8] Iteration [9] ncsim: *W,RNQUIE: Simulation is complete.
An unpacked array is used to refer to dimensions declared after the variable name.
Unpacked arrays may be fixed-size arrays, dynamic arrays, associative arrays or queues.
Single Dimensional Unpacked Array
module tb;
byte stack [8]; // depth = 8, 1 byte wide variable
initial begin
// Assign random values to each slot of the stack
foreach (stack[i]) begin
stack[i] = $random;
$display ("Assign 0x%0h to index %0d", stack[i], i);
end
// Print contents of the stack
$display ("stack = %p", stack);
end
endmodule
Simulation Log
Assign 0x24 to index 0
Assign 0x81 to index 1
Assign 0x9 to index 2
Assign 0x63 to index 3
Assign 0xd to index 4
Assign 0x8d to index 5
Assign 0x65 to index 6
Assign 0x12 to index 7
stack = '{'h24, 'h81, 'h9, 'h63, 'hd, 'h8d, 'h65, 'h12}
Multidimensional Unpacked Array
module tb;
byte stack [2][4]; // 2 rows, 4 cols
initial begin
// Assign random values to each slot of the stack
foreach (stack[i])
foreach (stack[i][j]) begin
stack[i][j] = $random;
$display ("stack[%0d][%0d] = 0x%0h", i, j, stack[i][j]);
end
// Print contents of the stack
$display ("stack = %p", stack);
end
endmodule
Simulation Log
ncsim> run
stack[0][0] = 0x24
stack[0][1] = 0x81
stack[0][2] = 0x9
stack[0][3] = 0x63
stack[1][0] = 0xd
stack[1][1] = 0x8d
stack[1][2] = 0x65
stack[1][3] = 0x12
stack = '{'{'h24, 'h81, 'h9, 'h63}, '{'hd, 'h8d, 'h65, 'h12}}
ncsim: *W,RNQUIE: Simulation is complete.
Packed + Unpacked Array
The example shown below illustrates a multidimensional packed + unpacked array.
module tb;
bit [3:0][7:0] stack [2][4]; // 2 rows, 4 cols
initial begin
// Assign random values to each slot of the stack
foreach (stack[i])
foreach (stack[i][j]) begin
stack[i][j] = $random;
$display ("stack[%0d][%0d] = 0x%0h", i, j, stack[i][j]);
end
// Print contents of the stack
$display ("stack = %p", stack);
// Print content of a given index
$display("stack[0][0][2] = 0x%0h", stack[0][0][2]);
end
endmodule
Simulation Log
ncsim> run
stack[0][0] = 0x12153524
stack[0][1] = 0xc0895e81
stack[0][2] = 0x8484d609
stack[0][3] = 0xb1f05663
stack[1][0] = 0x6b97b0d
stack[1][1] = 0x46df998d
stack[1][2] = 0xb2c28465
stack[1][3] = 0x89375212
stack = '{'{'h12153524, 'hc0895e81, 'h8484d609, 'hb1f05663}, '{'h6b97b0d, 'h46df998d, 'hb2c28465, 'h89375212}}
stack[0][0][2] = 0x15
ncsim: *W,RNQUIE: Simulation is complete.
In a multidimensional declaration, the dimensions declared before the name vary more faster than the dimensions following the name.
bit [1:4] m_var [1:5] // 1:4 varies faster than 1:5
bit m_var2 [1:5] [1:3] // 1:3 varies faster than 1:5
bit [1:3] [1:7] m_var3; // 1:7 varies faster than 1:3
bit [1:3] [1:2] m_var4 [1:7] [0:2] // 1:2 varies most rapidly, followed by 1:3, then 0:2 and then 1:7
UVM automation macros also include mechanisms to pack class variables into a bit or byte stream, and unpack a bit stream and populate the class contents. This is particularly useful when dealing with serial forms of communication like SPI, I2C and RS-232.
There are three main functions available to pack and unpack.
| Method | Description |
|---|---|
| pack | Performs a bit-wise concatenation of the class contents into an array of type bit |
| pack_bytes | Performs a bit-wise concatenation of the class contents into an array of type byte |
| pack_ints | Performs a bit-wise concatenation of the class contents into an array of type int |
| unpack | Extracts property values from an array of type bit and stores into correct class variable |
| unpack_bytes | Extracts property values from an array of type byte and stores into correct class variable |
| unpack_ints | Extracts property values from an array of type int and stores into correct class variable |
In the following examples, usage of all the three types of functions will be explored.
Using automation macros
Pack
A class called Packet is defined with some variables to store address and data, and is registered with `uvm_field_int macros to enable automation. UVM_DEFAULT specifies that all the default automation methods should be applied to the given variable.
Note that the order of variables as listed within `uvm_object_utils_* will be used for both packing and unpacking data.
class Packet extends uvm_object;
rand bit [3:0] m_addr;
rand bit [3:0] m_wdata;
rand bit [3:0] m_rdata;
rand bit m_wr;
`uvm_object_utils_begin(Packet)
`uvm_field_int(m_addr, UVM_DEFAULT)
`uvm_field_int(m_wdata, UVM_DEFAULT)
`uvm_field_int(m_rdata, UVM_DEFAULT)
`uvm_field_int(m_wr, UVM_DEFAULT)
`uvm_object_utils_end
function new(string name = "Packet");
super.new(name);
endfunction
endclass
Let us create a test class called pack_test where an object of Packet is created, randomized and packed.
class pack_test extends uvm_test;
`uvm_component_utils(pack_test)
function new(string name = "pack_test", uvm_component parent=null);
super.new(name, parent);
endfunction
// Declare some arrays to store packed data output from different pack functions
bit m_bits[];
byte unsigned m_bytes[];
int unsigned m_ints[];
virtual function void build_phase(uvm_phase phase);
// First create an object of class "Packet", randomize and print its contents
Packet m_pkt = Packet::type_id::create("Packet");
m_pkt.randomize();
m_pkt.print();
// Now, call "pack", "pack_bytes", and "pack_ints" and pass appropriate array type
m_pkt.pack(m_bits);
m_pkt.pack_bytes(m_bytes);
m_pkt.pack_ints(m_ints);
// Print the array contents
`uvm_info(get_type_name(), $sformatf("m_bits=%p", m_bits), UVM_LOW)
`uvm_info(get_type_name(), $sformatf("m_bytes=%p", m_bytes), UVM_LOW)
`uvm_info(get_type_name(), $sformatf("m_ints=%p", m_ints), UVM_LOW)
endfunction
endclass
module tb;
initial begin
run_test("pack_test");
end
endmodule
See that the function pack returned an array of bits, pack_bytes returned an array of bytes and pack_ints returned an array of ints. Note that pack_bytes padded 0 to the content from m_wr to turn it from 1 to 8.
UVM_INFO @ 0: reporter [RNTST] Running test pack_test...
--------------------------------
Name Type Size Value
--------------------------------
Packet Packet - @1907
m_addr integral 4 'hd
m_wdata integral 4 'h9
m_rdata integral 4 'h6
m_wr integral 1 'h1
--------------------------------
UVM_INFO testbench.sv(74) @ 0: uvm_test_top [pack_test] m_bits='{'h1, 'h1, 'h0, 'h1, 'h1, 'h0, 'h0, 'h1, 'h0, 'h1, 'h1, 'h0, 'h1}
UVM_INFO testbench.sv(75) @ 0: uvm_test_top [pack_test] m_bytes='{'hd9, 'h68}
UVM_INFO testbench.sv(76) @ 0: uvm_test_top [pack_test] m_ints='{3647471616}
UVM_INFO /playground_lib/uvm-1.2/src/base/uvm_report_server.svh(847) @ 0: reporter [UVM/REPORT/SERVER]
Unpack
Let us create a different test class called unpack_test which will create two Packet objects, but randomize only one of them leaving the other empty. Then pack contents of the first object into an array, and then unpack it into the second object and display its contents. Repeat the same thing with other types of pack functions.
class unpack_test extends uvm_test;
`uvm_component_utils(unpack_test)
function new(string name = "unpack_test", uvm_component parent=null);
super.new(name, parent);
endfunction
// Declare a few arrays to hold packed data for each type of "pack" function
bit m_bits[];
byte unsigned m_bytes[];
int unsigned m_ints[];
// Variables to hold return value from pack function
int m_val1, m_val2, m_val3;
virtual function void build_phase(uvm_phase phase);
Packet m_pkt = Packet::type_id::create("Packet");
Packet m_pkt2 = Packet::type_id::create("Packet");
`uvm_info(get_type_name(), $sformatf("Start pack"), UVM_LOW)
// Randomize the first object, print and pack into bit array, then display
m_pkt.randomize();
m_pkt.print();
m_pkt.pack(m_bits);
`uvm_info(get_type_name(), $sformatf("packed m_bits=%p", m_bits), UVM_LOW)
// Randomize the first object, print and pack into byte array, then display
m_pkt.randomize();
m_pkt.print();
m_pkt.pack_bytes(m_bytes);
`uvm_info(get_type_name(), $sformatf("packed m_bytes=%p", m_bytes), UVM_LOW)
// Randomize the first object, print and pack into int array, then display
m_pkt.randomize();
m_pkt.print();
m_pkt.pack_ints(m_ints);
`uvm_info(get_type_name(), $sformatf("packed m_ints=%p", m_ints), UVM_LOW)
`uvm_info(get_type_name(), $sformatf("Start unpack"), UVM_LOW)
// Now unpack the packed bit array into the second object, and display
m_val1 = m_pkt2.unpack(m_bits);
`uvm_info(get_type_name(), $sformatf("unpacked m_val1=0x%0h", m_val1), UVM_LOW)
m_pkt2.print();
// Now unpack the packed byte array into the second object, and display
m_val2 = m_pkt2.unpack_bytes(m_bytes);
`uvm_info(get_type_name(), $sformatf("unpacked m_val2=0x%0h", m_val2), UVM_LOW)
m_pkt2.print();
// Now unpack the packed int array into the second object, and display
m_val3 = m_pkt2.unpack_ints(m_ints);
`uvm_info(get_type_name(), $sformatf("unpacked m_val3=0x%0h", m_val3), UVM_LOW)
m_pkt2.print();
endfunction
endclass
module tb;
initial begin
run_test("unpack_test");
end
endmodule
Remember that the order in which it is packed should be same as the order in which it is unpacked. Any change in packer policy regarding order may cause the results to be different.
Simulation LogUVM_INFO @ 0: reporter [RNTST] Running test unpack_test... UVM_INFO testbench.sv(93) @ 0: uvm_test_top [unpack_test] Start pack -------------------------------- Name Type Size Value -------------------------------- Packet Packet - @1907 m_addr integral 4 'hd m_wdata integral 4 'h9 m_rdata integral 4 'h6 m_wr integral 1 'h1 -------------------------------- UVM_INFO testbench.sv(95) @ 0: uvm_test_top [unpack_test] packed m_bits='{'h1, 'h1, 'h0, 'h1, 'h1, 'h0, 'h0, 'h1, 'h0, 'h1, 'h1, 'h0, 'h1} -------------------------------- Name Type Size Value -------------------------------- Packet Packet - @1907 m_addr integral 4 'h8 m_wdata integral 4 'he m_rdata integral 4 'h4 m_wr integral 1 'h0 -------------------------------- UVM_INFO testbench.sv(100) @ 0: uvm_test_top [unpack_test] packed m_bytes='{'h8e, 'h40} -------------------------------- Name Type Size Value -------------------------------- Packet Packet - @1907 m_addr integral 4 'h9 m_wdata integral 4 'he m_rdata integral 4 'he m_wr integral 1 'h1 -------------------------------- UVM_INFO testbench.sv(105) @ 0: uvm_test_top [unpack_test] packed m_ints='{2666004480} UVM_INFO testbench.sv(109) @ 0: uvm_test_top [unpack_test] Start unpack UVM_INFO testbench.sv(109) @ 0: uvm_test_top [unpack_test] unpacked m_val1=0xd -------------------------------- Name Type Size Value -------------------------------- Packet Packet - @1909 m_addr integral 4 'hd m_wdata integral 4 'h9 m_rdata integral 4 'h6 m_wr integral 1 'h1 -------------------------------- UVM_INFO testbench.sv(113) @ 0: uvm_test_top [unpack_test] unpacked m_val2=0xd -------------------------------- Name Type Size Value -------------------------------- Packet Packet - @1909 m_addr integral 4 'h8 m_wdata integral 4 'he m_rdata integral 4 'h4 m_wr integral 1 'h0 -------------------------------- UVM_INFO testbench.sv(117) @ 0: uvm_test_top [unpack_test] unpacked m_val3=0xd -------------------------------- Name Type Size Value -------------------------------- Packet Packet - @1909 m_addr integral 4 'h9 m_wdata integral 4 'he m_rdata integral 4 'he m_wr integral 1 'h1 -------------------------------- UVM_INFO /playground_lib/uvm-1.2/src/base/uvm_report_server.svh(847) @ 0: reporter [UVM/REPORT/SERVER]
Automation macros introduce a lot of new code and is not generally recommemded to be used
Using do_pack/do_unpack
Just like print, copy and compare, pack and unpack also has user definable hooks called do_pack and do_unpack.
class Packet extends uvm_object;
rand bit [3:0] m_addr;
rand bit [3:0] m_wdata;
rand bit [3:0] m_rdata;
rand bit m_wr;
`uvm_object_utils(Packet)
// Define do_print, so that print method displays contents of this class
virtual function void do_print(uvm_printer printer);
super.do_print(printer);
printer.print_field_int("m_addr", m_addr, $bits(m_addr), UVM_HEX);
printer.print_field_int("m_wdata", m_wdata, $bits(m_wdata), UVM_HEX);
printer.print_field_int("m_rdata", m_rdata, $bits(m_rdata), UVM_HEX);
printer.print_field_int("m_wr", m_wr, $bits(m_wr), UVM_HEX);
endfunction
virtual function void do_pack(uvm_packer packer);
super.do_pack(packer);
packer.pack_field_int(m_addr, $bits(m_addr));
packer.pack_field_int(m_wdata, $bits(m_wdata));
packer.pack_field_int(m_rdata, $bits(m_rdata));
packer.pack_field_int(m_wr, $bits(m_wr));
endfunction
virtual function void do_unpack(uvm_packer packer);
super.do_pack(packer);
m_addr = packer.unpack_field_int($bits(m_addr));
m_wdata = packer.unpack_field_int($bits(m_wdata));
m_rdata = packer.unpack_field_int($bits(m_rdata));
m_wr = packer.unpack_field_int($bits(m_wr));
endfunction
function new(string name = "Packet");
super.new(name);
endfunction
endclass
The same set of tests shown above can be run with this class and will yield the same results.
UVM uses the concept of a factory where all objects are registered with it so that it can return an object of the requested type when required. The utility macros help to register each object with the factory.
UVM also introduces a bunch of automation mechanisms for implementing print, copy, and compare objects and are defined using the field macros.
Utility Macros
The utils macro is used primarily to register an object or component with the factory and is required for it to function correctly. It is required to be used inside every user-defined class that is derived from uvm_object which includes all types of sequence items and components.
Object Utility
All classes derived directly from uvm_object or uvm_transaction require them to be registered using `uvm_object_utils macro. Note that it is mandatory for the new function to be explicitly defined for every class, and takes the name of the class instance as an argument.
class ABC extends uvm_object;
// Register this user defined class with the factory
`uvm_object_utils(ABC)
function new(string name = "ABC");
super.new(name);
endfunction
endclass
Component Utility
All classes derived directly or indirectly from uvm_component require them to be registered with the factory using `uvm_component_utils macro. Note that it is mandatory for the new function to be explicitly defined for every class derived directly or indirectly from uvm_component and takes the name of the class instance and a handle to the parent class where this object is instantiated.
class DEF extends uvm_component;
// Class derived from uvm_component, register with factory
`uvm_component_utils(DEF)
function new(string name = "DEF", uvm_component parent=null);
super.new(name, parent);
endfunction
endclass
Macro Expansion: Behind the Scenes
`uvm_object_utils eventually gets expanded into its *_begin and *_end form with nothing between the begin and end. *_begin implements other macros required for the correct functionality of UVM factory.
// Empty uvm_object_utils macro
`define uvm_object_utils(T)
`uvm_object_utils_begin(T)
`uvm_object_utils_end
`define uvm_object_utils_begin(T)
`m_uvm_object_registry_internal(T,T) // Sub-macro #1
`m_uvm_object_create_func(T) // Sub-macro #2
`m_uvm_get_type_name_func(T) // Sub-macro #3
`uvm_field_utils_begin(T) // Sub-macro #4
// uvm_object_utils_end simply terminates a function started
// somewhere in the middle
`define uvm_object_utils_end
end
endfunction
It can be seen from the code shown below that each macro expanded by *_begin implements some functions required for factory operation and performs the following steps.
- Implements
get_typestatic method which basically returns a factory proxy object for the requested type. - Implements
create, which instantiates an object of the specified type by calling its constructor with no arguments. - Implements
get_type_namemethod which returns the type as a string - Registers the type with UVM factory
// Sub-macro #1. Implement the functions "get_type()" and "get_object_type()"
`define m_uvm_object_registry_internal(T,S)
typedef uvm_object_registry#(T,`"S`") type_id;
static function type_id get_type();
return type_id::get();
endfunction
virtual function uvm_object_wrapper get_object_type();
return type_id::get();
endfunction
// Sub-macro #2. Implement the function "create()"
`define m_uvm_object_create_func(T)
function uvm_object create (string name="");
T tmp;
`ifdef UVM_OBJECT_DO_NOT_NEED_CONSTRUCTOR
tmp = new();
if (name!="")
tmp.set_name(name);
`else
if (name=="") tmp = new();
else tmp = new(name);
`endif
return tmp;
endfunction
// Sub-macro #3. Implement the function "get_type_name()"
`define m_uvm_get_type_name_func(T)
const static string type_name = `"T`";
virtual function string get_type_name ();
return type_name;
endfunction
// Sub-macro #4. Implement field automation macros
`define uvm_field_utils_begin(T)
function void __m_uvm_field_automation (uvm_object tmp_data__,
int what__,
string str__);
...
In a similar way, `uvm_component_utils_* also has equivalent macros and function calls. Note that the create function for components take two arguments, name and parent, unlike that of an object.
Paratemerized classes should use `uvm_object_param_utils_* since they do not have to give a type during factory registration.
Creation of class object
It is recommended that all class objects are created by calling the type_id::create() method which is already defined using the macro `m_uvm_object_create_func. This makes any child class object to be created and returned using factory mechanism and promotes testbench flexibility and reusability.
class ABC extends uvm_object;
`uvm_object_utils(ABC)
function new(string name = "ABC");
super.new(name);
endfunction
endclass
class base_test extends uvm_test;
`uvm_component_utils(base_test)
function new(string name = "base_test", uvm_component parent=null);
super.new(name, parent);
endfunction
virtual function void build_phase(uvm_phase phase);
// An object of class "ABC" is instantiated in UVM by calling
// its "create()" function which has been defined using a macro
// as shown above
ABC abc = ABC::type_id::create("abc_inst");
endfunction
endclass
Field Macros
`uvm_field_* macros that were used between *_begin and *_end utility macros are basically called field macros since they operate on class properties and provide automatic implementations of core methods like copy, compare and print. This helps the user save some time from implementing custom do_copy, do_compare and do_print functions for each and every class. However, since these macros are expanded into general code, it may impact simulation performance and are generally not recommended.
Usage Example
class ABC extends uvm_object;
rand bit [15:0] m_addr;
rand bit [15:0] m_data;
`uvm_object_utils_begin(ABC)
`uvm_field_int(m_addr, UVM_DEFAULT)
`uvm_field_int(m_data, UVM_DEFAULT)
`uvm_object_utils_end
function new(string name = "ABC");
super.new(name);
endfunction
endclass
The `uvm_field_* corresponding to the data type of each variable should be used. For example, variables of type int, bit, byte should use `uvm_field_int, while variables of type string should use `uvm_field_string and so on. The macro accepts atleast two arguments: ARG and FLAG.
| Argument | Description |
|---|---|
| ARG | Name of the variable, whose type should be appropriate for the macro that is used |
| FLAG | When set to something other than UVM_DEFAULT or UVM_ALL_ON, it specifies which data method implementations will not be included. For example, if FLAG is set to NO_COPY, everything else will be implemented for the variable except copy. |
The field FLAG can take the following values and multiple values can be OR'ed together. A combination of these flags determine the kind of operations that are allowed to be done on the given variable.
| Flag | Description |
|---|---|
| UVM_ALL_ON | All operations are turned on |
| UVM_DEFAULT | Enables all operations and equivalent to UVM_ALL_ON |
| UVM_NOCOPY | Do not copy the given variable |
| UVM_NOCOMPARE | Do not compare the given variable |
| UVM_NOPRINT | Do not print the given variable |
| UVM_NOPACK | Do not pack or unpack the given variable |
| UVM_REFERENCE | Operate only on handles, i.e. for object types, do not do deep copy, etc |
Along with control on operations, `uvm_field_* macros also provide some control on the radix of the given variable which can take the following values. This value can be OR'ed with the operational flags listed in the table above. UVM_HEX is the default radix if none is specified.
| Radix | Description |
|---|---|
| UVM_BIN | Print/record the given variable in binary format |
| UVM_DEC | Print/record the given variable in decimal format |
| UVM_HEX | Print/record the given variable in hexadecimal format |
| UVM_OCT | Print/record the given variable in octal format |
| UVM_STRING | Print/record the given variable in string format |
| UVM_TIME | Print/record the given variable in time format |
See more examples of field macros in print, copy, and compare and pack