In a random verification environment where data objects are being continuously generated and operated upon by different components, debug would become easier if contents of an object can be displayed.
Old-school style
Traditionally this is done by printing out values to either a logfile or screen via $display statements and custom print functions.
class Packet;
bit [31:0] addr;
int count_id;
bit [3:0] length;
...
function display ();
$display ("addr=0x%0h count_id=0x%0h length=0x%0h", p1.addr, p1.count_id, p1.length);
endfunction
endclass
module tb;
initial begin
Packet p1 = new();
p1.display();
end
endmodule
There was no built-in print mechanisms for a class which made testbench developers to write customized versions of print functions for every class like the display() method in the snippet above.
How its done in UVM
UVM avoids the need for customized print functions by incorporating its own uvm_printer class that takes care of all the required configurations to print class properties. It makes sense to include print features in uvm_object so that all child classes will automatically gain access to those features.
Every class item derived from uvm_object will have a printer instance within it. So, a data class derived from uvm_sequence_item or uvm_component will have access to the print() function as well. The major advantage UVM provides are the `uvm_field_* macros that automates the process of writing special print methods.
virtual class uvm_object extends uvm_void;
...
function void print (uvm_printer printer=null);
if (printer==null)
printer = uvm_default_printer;
...
endfunction
...
endclass
Styles
There are three main printers in UVM and have the following display formats.
- Table printer
--------------------------------------------------- Name Type Size Value --------------------------------------------------- c1 container - @1013 d1 mydata - @1022 v1 integral 32 'hcb8f1c97 e1 enum 32 THREE str string 2 hi value integral 12 'h2d ---------------------------------------------------
c1: (container@1013) {
d1: (mydata@1022) {
v1: 'hcb8f1c97
e1: THREE
str: hi
}
value: 'h2d
}
c1: (container@1013) { d1: (mydata@1022) { v1: 'hcb8f1c97 e1: THREE str: hi } value: 'h2d }
Usage
By default, UVM assigns table printer to handle every print() function, and hence is the uvm_default_printer. For convenience, global instances of each printer type are available for direct reference in your testbenches.
uvm_table_printer uvm_default_table_printer = new();
uvm_tree_printer uvm_default_tree_printer = new();
uvm_line_printer uvm_default_line_printer = new();
uvm_printer uvm_default_printer = uvm_default_table_printer;
You can pass any of the three printer instance to the print() function to make it print in that particular style. Remember that the print() function receives a printer object.
class my_data extends uvm_sequence_item;
bit [2:0] mode;
endclass
my_data obj0;
obj0.print (); // Calls table printer by default
obj0.print (uvm_default_line_printer); // Calls line printer
Conditions
Calling print() is only possible if you do either of the two things.
- Add any member that needs to be printed, within
`uvm_object_utils_beginand`uvm_object_utils_end
class my_data extends uvm_sequence_item;
rand bit [7:0] data;
rand bit [7:0] addr;
constraint c_addr { addr > 0; addr < 8;}
`uvm_object_utils_begin (my_data)
`uvm_field_int (data, UVM_ALL_ON)
`uvm_field_int (addr, UVM_ALL_ON)
`uvm_object_utils_end
function new (string name = "my_data");
super.new (name);
endfunction
endclass
By applying variables to the macros, UVM automates these members to be included in the common utilties defined in uvm_object class namely, print(), copy(), compare(), etc
do_print() function for the class
class derivative extends my_data;
`uvm_object_utils (derivative)
rand bit [2:0] mode;
function new (string name="derivative");
super.new (name);
endfunction
virtual function void do_print (uvm_printer printer);
printer.print_int ("mode", mode, $bits(mode));
`uvm_info ("DVR", "do_print called", UVM_MEDIUM)
endfunction
endclass
If you did not use the utils_begin/end macros, you should define the do_print() method. Remember to use functions within the uvm_printer class to print.
Note that you can also do both the approaches together. The do_print() method will simply append whatever it is provided with to the macro.
class derivative extends my_data;
rand bit [2:0] mode;
rand bit [1:0] format;
`uvm_object_utils_begin (derivative)
`uvm_field_int (format, UVM_ALL_ON)
`uvm_object_utils_end
function new (string name="derivative");
super.new (name);
endfunction
virtual function void do_print (uvm_printer printer);
printer.print_int ("mode", mode, $bits(mode));
`uvm_info ("DVR", "do_print called", UVM_MEDIUM)
endfunction
endclass
Knobs
There is an instance of a class called uvm_printer_knobs within every printer. This can be used to change some of the settings and parameters used by the print() function.
uvm_default_printer.knobs.size = 0; // Will not display the size column
uvm_default_printer.knobs.indent = 4; // Indents to the right by 4 spaces instead of the default 2
uvm_default_printer.hex_radix = "0x"; // Replaces the hex radix of 'h with 0x
Example
First, we'll define a few data item objects. colors is nested inside format, which is inturn nested in the class my_data to create a nested hierarchy.
//---------------------- colors --------------------------
class colors extends uvm_sequence_item;
rand bit [3:0] color;
rand bit enable;
`uvm_object_utils_begin (colors)
`uvm_field_int (color, UVM_ALL_ON)
`uvm_field_int (enable, UVM_ALL_ON)
`uvm_object_utils_end
endclass
//---------------------- format --------------------------
class format extends uvm_sequence_item;
rand bit [3:0] header;
rand bit [2:0] footer;
rand bit enable;
rand bit [1:0] body;
rand colors m_color;
`uvm_object_utils_begin (format)
`uvm_field_int (header, UVM_ALL_ON)
`uvm_field_int (footer, UVM_ALL_ON)
`uvm_field_int (enable, UVM_ALL_ON)
`uvm_field_int (body, UVM_ALL_ON)
`uvm_object_utils_end
function new (string name = "format");
super.new (name);
m_color = colors::type_id::create ("m_color");
endfunction
virtual function void do_print (uvm_printer printer);
printer.print_object ("m_color", m_color);
endfunction
endclass
//---------------------- my_data --------------------------
class my_data extends uvm_sequence_item;
rand format m_format0;
rand bit [7:0] data;
rand bit [7:0] addr;
constraint c_addr { addr > 0; addr < 8;}
`uvm_object_utils_begin (my_data)
`uvm_field_int (data, UVM_ALL_ON)
`uvm_field_int (addr, UVM_ALL_ON)
`uvm_field_object (m_format0, UVM_ALL_ON)
`uvm_object_utils_end
function new (string name = "my_data");
super.new (name);
m_format0 = format::type_id::create ("m_format0");
endfunction
endclass
//---------------------- derivative --------------------------
class derivative extends my_data;
`uvm_object_utils (derivative)
rand bit [2:0] mode;
function new (string name="derivative");
super.new (name);
endfunction
virtual function void do_print (uvm_printer printer);
printer.knobs.depth=0;
printer.print_int ("mode", mode, $bits(mode));
`uvm_info ("DVR", "do_print called", UVM_MEDIUM)
endfunction
endclass
Note the following for the code shown above:
- All the members of the class colors are added to the
`uvm_object_utils_begin/endmacro - All the class objects have to be instantiated either using
new()ortype_id::create() - In class format, all members except m_color is used in the macro, while m_color is used inside
do_print()method - Class derivative adds the mode via
do_print()method.
class base_test extends uvm_test;
`uvm_component_utils (base_test)
my_data obj0;
derivative dv0;
uvm_table_printer tprinter;
function new (string name = "base_test", uvm_component parent);
super.new (name, parent);
endfunction
virtual function void build_phase (uvm_phase phase);
super.build_phase (phase);
obj0 = my_data::type_id::create ("obj0");
dv0 = derivative::type_id::create ("dv0");
tprinter = new();
cfg_printer();
endfunction
virtual task run_phase (uvm_phase phase);
void'(obj0.randomize());
`uvm_info ("TST", "print() called with no arguments", UVM_MEDIUM)
obj0.print (); // uses uvm_default_printer
`uvm_info ("TST", "Calling print (uvm_default_line_printer)", UVM_MEDIUM)
obj0.print (uvm_default_line_printer);
`uvm_info ("TST", "Calling print (uvm_default_tree_printer)", UVM_MEDIUM)
obj0.print (uvm_default_tree_printer);
`uvm_info ("TST", "Calling print (uvm_default_table_printer)", UVM_MEDIUM)
obj0.print (uvm_default_table_printer);
`uvm_info ("TST", "Calling print (tprinter)", UVM_MEDIUM)
obj0.print (tprinter);
`uvm_info ("TST", "Print derivative (tprinter)", UVM_MEDIUM)
dv0.print (uvm_default_table_printer);
endtask
// Configuration to change display settings for the printer
virtual function void cfg_printer ();
tprinter.knobs.full_name = 1; // Show full name of the variable relative to class instance
tprinter.knobs.size = 0; // Do not show size column
tprinter.knobs.depth = 1; // Only show upto 1 level of the nested hierarchy
tprinter.knobs.reference = 2; // Do not print object ID handles
tprinter.knobs.type_name = 0; // Do not show Type column
tprinter.knobs.indent = 4; // Indent from the left by 4
tprinter.knobs.hex_radix = "0x"; // Replace 'h radix by 0x - observe Value field to see this
endfunction
endclass
----------------------------------------------------------------
CDNS-UVM-1.1d (14.22-s009)
(C) 2007-2013 Mentor Graphics Corporation
(C) 2007-2013 Cadence Design Systems, Inc.
(C) 2006-2013 Synopsys, Inc.
(C) 2011-2013 Cypress Semiconductor Corp.
----------------------------------------------------------------
UVM_INFO @ 0: reporter [RNTST] Running test base_test...
UVM_INFO ./tb/test_pkg.sv(34) @ 0: uvm_test_top [TST] print() called with no arguments
-----------------------------------
Name Type Size Value
-----------------------------------
obj0 my_data - @2687
data integral 8 'h5a
addr integral 8 'h1
m_format0 format - @2700
header integral 4 'hb
footer integral 3 'h0
enable integral 1 'h1
body integral 2 'h1
m_color colors - @2711
color integral 4 'h8
enable integral 1 'h0
-----------------------------------
UVM_INFO ./tb/test_pkg.sv(37) @ 0: uvm_test_top [TST] Calling print (uvm_default_line_printer)
obj0: (my_data@2687) { data: 'h5a addr: 'h1 m_format0: (format@2700) { header: 'hb footer: 'h0 enable: 'h1 body: 'h1 m_color: (colors@2711) { color: 'h8 enable: 'h0 } } }
UVM_INFO ./tb/test_pkg.sv(40) @ 0: uvm_test_top [TST] Calling print (uvm_default_tree_printer)
obj0: (my_data@2687) {
data: 'h5a
addr: 'h1
m_format0: (format@2700) {
header: 'hb
footer: 'h0
enable: 'h1
body: 'h1
m_color: (colors@2711) {
color: 'h8
enable: 'h0
}
}
}
UVM_INFO ./tb/test_pkg.sv(43) @ 0: uvm_test_top [TST] Calling print (uvm_default_table_printer)
-----------------------------------
Name Type Size Value
-----------------------------------
obj0 my_data - @2687
data integral 8 'h5a
addr integral 8 'h1
m_format0 format - @2700
header integral 4 'hb
footer integral 3 'h0
enable integral 1 'h1
body integral 2 'h1
m_color colors - @2711
color integral 4 'h8
enable integral 1 'h0
-----------------------------------
UVM_INFO ./tb/test_pkg.sv(46) @ 0: uvm_test_top [TST] Calling print (tprinter)
-------------------------
Name Value
-------------------------
obj0 -
obj0.data 0x5a
obj0.addr 0x1
obj0.m_format0 -
-------------------------
UVM_INFO ./tb/test_pkg.sv(49) @ 0: uvm_test_top [TST] Print derivative (tprinter)
UVM_INFO ./tb/my_pkg.sv(94) @ 0: reporter@@dv0 [DVR] do_print called
-------------------------------------
Name Type Size Value
-------------------------------------
dv0 derivative - @2722
data integral 8 'h0
addr integral 8 'h0
m_format0 format - @2732
header integral 4 'h0
footer integral 3 'h0
enable integral 1 'h0
body integral 2 'h0
m_color colors - @2741
color integral 4 'h0
enable integral 1 'h0
mode integral 3 'h0
-------------------------------------
--- UVM Report catcher Summary ---
