UVM实用技巧【一】
今天介绍几个UVM中较为实用的函数，在能够辅助大家调试环境。
打印环境拓扑结构
有时候，我们可能由于某些原因，组件可能层次安排不对，或者组件没有create，但是自己却没有注意到。或者我们想要看看环境的整体结构，那么就能用方法uvm_top.print_topology()打印整个拓扑结构。
它的函数原型是
function void print_topology (
uvm_printer printer = null
)
UVM对他的解释是
Print the verification environment’s component topology. The printer is a uvm_printer object that controls the format of the topology printout; a null printer prints with the default output.
这个方法属于uvm_root类，我们在调用时，直接实用uvm_top这个句柄即可，这个句柄类型就是uvm_root，并且全局可见。例如，通过如下代码，就能在run_phase阶段打印
task run_phase(uvm_phase phase);
super.run_phase(phase);
uvm_top.print_topology();
endtask : run_phase
打印信息如下
------------------------------------------------------------
Name Type Size Value
------------------------------------------------------------
uvm_test_top my_test - @466
m_env my_env - @473
m_driver my_driver - @484
rsp_port uvm_analysis_port - @499
seq_item_port uvm_seq_item_pull_port - @491
m_sequencer my_sequencer - @507
rsp_export uvm_analysis_export - @514
seq_item_export uvm_seq_item_pull_imp - @608
arbitration_queue array 0 -
lock_queue array 0 -
num_last_reqs integral 32 'd1
num_last_rsps integral 32 'd1
------------------------------------------------------------
能过够很清晰的看到各个组件，以及接口，甚至ID。
方法默认的参数是uvm_printer printer = null有兴趣的读者可以自行了解UVM打打印机制
统计config情况
config为验证环境中的数据传递提供了很方便的方法，通常用来传递一些静态配置，还有virtual interface。也可以用来启动sequence。但是有时，错误的实用方式，例如路径不对，会导致数据传输失败，因此，UVM提供了一个方法用于统计config的set和get情况。
函数原型为
function void check_config_usage (
bit recurse = 1
)
UVM的注释为
Check all configuration settings in a components configuration table to determine if the setting has been used, overridden or not used. When recurse is 1 (default), configuration for this and all child components are recursively checked. This function is automatically called in the check phase, but can be manually called at any time.
例如，在test中
function void build_phase(uvm_phase phase);
super.build_phase(phase);
m_env=my_env::type_id::create("m_env",this);
uvm_config_db#(uvm_object_wrapper)::set(this, "m_env.m_sequencer.main_phase", "default_sequence",my_sequence::type_id::get());
endfunction : build_phase
task run_phase(uvm_phase phase);
super.run_phase(phase);
check_config_usage();
endtask : run_phase
打印信息为
UVM_INFO @ 0: uvm_test_top [CFGNRD] ::: The following resources have at least one write and no reads :::
default_sequence [/^uvm_test_top\.m_env\.m_sequencer\.main_phase$/] : (class uvm_pkg::uvm_object_wrapper) {my_sequence} @uvm_object_registry__36@1
-
--------
uvm_test_top reads: 0 @ 0 writes: 1 @ 0
这个时候default_sequence还没有启动，所以写了一次，还没被读，如果加上了延时，或者在run_phase之后调用，那么就不会产生任何信息。
检查configdb的配置
有时候，一不小心写错config的路径，就会导致失败，但是自己又眼睛不好使，看不出自己那些错了，反复检查，层次并没有问题，但是就是并没有错。UVM提供了一个函数，用于查询config db的是否存在某个数据。
函数原型为
static function bit exists(
uvm_component cntxt,
string inst_name,
string field_name,
bit spell_chk =
)
这是config_db的一个静态函数，在调用时和set是一样的。UVM对此的注释是
Check if a value for field_name is available in inst_name, using component cntxt as the starting search point. inst_name is an explicit instance name relative to cntxt and may be an empty string if the cntxt is the instance that the configuration object applies to. field_name is the specific field in the scope that is being searched for. The spell_chk arg can be set to 1 to turn spell checking on if it is expected that the field should exist in the database. The function returns 1 if a config parameter exists and 0 if it doesn’t exist.
最后一个参数为1时会进行拼写检查，帮你匹配相近的路径。如果存在便会返回1，否则，0
例如，我们在test中使用default_sequence启动，但是发现无论如何都没有效果，那么我们可以在sequencer中用如下方式检查
class my_sequencer extends uvm_sequencer #(my_item);
`uvm_component_utils(my_sequencer)
function new (string name = "my_sequencer", uvm_component parent);
super.new(name, parent);
endfunction
task main_phase(uvm_phase phase);
super.main_phase(phase);
uvm_config_db#(uvm_object_wrapper)::exists(this,"","default_sequence",1);
endtask
endclass: my_sequencer
class my_test extends uvm_test;
my_env m_env;
`uvm_component_utils(my_test)
function new(string name = "my_test", uvm_component parent=null);
super.new(name, parent);
endfunction : new
function void build_phase(uvm_phase phase);
super.build_phase(phase);
m_env=my_env::type_id::create("m_env",this);
uvm_config_db#(uvm_object_wrapper)::set(this, "m_env.m_sequencer.main_phase", "default_sequnce",my_sequence::type_id::get());
endfunction : build_phase
endclass : my_test
你发现哪里有问题了吗，上面的例子运行的结果是
default_sequence not located
did you mean default_sequnce?
你会收获来自UVM的无情嘲讽，是的，没错，少打了一个e
完整代码
package lab_pkg;
import uvm_pkg::*;
`include "uvm_macros.svh"
class my_item extends uvm_sequence_item;
`uvm_object_utils(my_item)
function new (string name = "my_item");
super.new(name);
endfunction
endclass
class my_driver extends uvm_driver#(my_item);
`uvm_component_utils(my_driver)
// Constructor
function new(string name = "my_driver", uvm_component parent=null);
super.new(name, parent);
endfunction : new
task run_phase(uvm_phase phase);
my_item req,rsp;
super.run_phase(phase);
uvm_top.print_topology();
check_config_usage();
forever begin
seq_item_port.get_next_item(req);
#100;
`uvm_info(get_type_name,"get a item",UVM_LOW)
void'($cast(rsp, req.clone()));
rsp.set_sequence_id(req.get_sequence_id());
seq_item_port.item_done(rsp);
end
endtask : run_phase
endclass : my_driver
class my_sequencer extends uvm_sequencer #(my_item);
`uvm_component_utils(my_sequencer)
function new (string name = "my_sequencer", uvm_component parent);
super.new(name, parent);
endfunction
task main_phase(uvm_phase phase);
super.main_phase(phase);
uvm_config_db#(uvm_object_wrapper)::exists(this,"","default_sequence",1);
endtask
endclass: my_sequencer
class my_sequence extends uvm_sequence #(my_item);
`uvm_object_utils(my_sequence)
function new (string name = "my_sequence");
super.new(name);
endfunction
task body();
if(starting_phase!=null)
starting_phase.raise_objection(this);
send_trans();
if (starting_phase!=null) begin
starting_phase.drop_objection(this);
end
endtask
task send_trans();
my_item req, rsp;
`uvm_do(req)
`uvm_info(get_type_name(), req.sprint(), UVM_HIGH)
get_response(rsp);
`uvm_info(get_type_name(), rsp.sprint(), UVM_HIGH)
endtask
endclass: my_sequence
class my_env extends uvm_env;
my_driver m_driver;
my_sequencer m_sequencer;
`uvm_component_utils(my_env)
function new(string name = "my_env", uvm_component parent=null);
super.new(name, parent);
endfunction : new
function void build_phase(uvm_phase phase);
super.build_phase(phase);
m_driver=my_driver::type_id::create("m_driver",this);
m_sequencer=my_sequencer::type_id::create("m_sequencer",this);
endfunction : build_phase
function void connect_phase(uvm_phase phase);
super.connect_phase(phase);
m_driver.seq_item_port.connect(m_sequencer.seq_item_export);
endfunction : connect_phase
endclass : my_env
class my_test extends uvm_test;
my_env m_env;
`uvm_component_utils(my_test)
// Constructor
function new(string name = "my_test", uvm_component parent=null);
super.new(name, parent);
endfunction : new
function void build_phase(uvm_phase phase);
super.build_phase(phase);
m_env=my_env::type_id::create("m_env",this);
uvm_config_db#(uvm_object_wrapper)::set(this, "m_env.m_sequencer.main_phase", "default_sequnce",my_sequence::type_id::get());
endfunction : build_phase
task run_phase(uvm_phase phase);
super.run_phase(phase);
endtask : run_phase
endclass : my_test
endpackage : lab_pkg
tb代码为
module tb ();
import uvm_pkg::*;
import lab_pkg::*;
`include "uvm_macros.svh"
initial begin
run_test("my_test");
end
endmodule : tb
