In simple terms it's a UVM sequencer that contain handles to other sequencers. Why do we need this ? Because we plan to use virtual sequences and want to have control over all sequencers from a central place. A request type is not required here because this sequencer is generic and not limited to handle only one particular data type.
Click to refresh the concept of a virtual sequence.
The environment shown above has an APB agent, Wishbone agent, PCIE environment and a register layer environment. Each of these components have their own sequences and the respective sequencers on which they are launched. A virtual sequencer called m_virt_seqr is instantiated to hold references to each individual sequencer. Hence a virtual sequence executing on this virtual sequencer will have access to all the sequencers in the testbench.
Example
class my_virtual_sequencer extends uvm_sequencer;
`uvm_component_utils (my_virtual_sequencer)
function new (string name = "my_virtual_sequencer", uvm_component parent);
super.new (name, parent);
endfunction
// Declare handles to other sequencers here
apb_sequencer m_apb_seqr;
reg_sequencer m_reg_seqr;
wb_sequencer m_wb_seqr;
pcie_sequencer m_pcie_seqr;
endclass
In our top environment, we'll create an instance of the virtual sequencer and connect real sequencers with their respective handles in the virtual sequencer.
class top_env extends uvm_env;
...
my_virtual_sequencer m_virt_seqr;
virtual function void build_phase (uvm_phase phase);
...
m_virt_seqr = my_virtual_sequencer::type_id::create ("m_virt_seqr", this);
...
endfunction
// Connect virtual sequencer handles to actual sequencers
virtual function void connect_phase (uvm_phase phase);
...
m_virt_seqr.m_apb_seqr = m_apb_agent.m_apb_seqr;
m_virt_seqr.m_reg_seqr = m_reg_env.m_reg_seqr;
m_virt_seqr.m_pcie_seqr = m_pcie_env.m_pcie_agent.m_pcie_seqr;
...
endfunction
endclass
A virtual sequencer operates best when used with a virtual sequence. Read more on Virtual Sequence.
Go to the Downloads page for example code under tag "virtual-sequencer".
Simulation Log
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CDNS-UVM-1.1d
(C) 2007-2013 Mentor Graphics Corporation
(C) 2007-2013 Cadence Design Systems, Inc.
(C) 2006-2013 Synopsys, Inc.
(C) 2011-2013 Cypress Semiconductor Corp.
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UVM_INFO @ 0: reporter [RNTST] Running test base_test...
UVM_INFO @ 0: reporter [UVMTOP] UVM testbench topology:
--------------------------------------------------------------
Name Type Size Value
--------------------------------------------------------------
uvm_test_top base_test - @2667
m_top_env top_env - @2733
m_apb_agent apb_agent - @2780
m_apb_drv apb_driver - @4089
rsp_port uvm_analysis_port - @4237
seq_item_port uvm_seq_item_pull_port - @4188
m_apb_mon apb_monitor - @4217
m_apb_seqr uvm_sequencer - @3512
rsp_export uvm_analysis_export - @3569
seq_item_export uvm_seq_item_pull_imp - @4109
arbitration_queue array 0 -
lock_queue array 0 -
num_last_reqs integral 32 'd1
num_last_rsps integral 32 'd1
m_spi_agent spi_agent - @2840
m_spi_drv spi_driver - @4897
rsp_port uvm_analysis_port - @5043
seq_item_port uvm_seq_item_pull_port - @4995
m_spi_mon spi_monitor - @5024
m_spi_seqr uvm_sequencer - @4321
rsp_export uvm_analysis_export - @4377
seq_item_export uvm_seq_item_pull_imp - @4917
arbitration_queue array 0 -
lock_queue array 0 -
num_last_reqs integral 32 'd1
num_last_rsps integral 32 'd1
m_virt_seq virtual_sequencer - @2870
rsp_export uvm_analysis_export - @2928
seq_item_export uvm_seq_item_pull_imp - @3478
arbitration_queue array 0 -
lock_queue array 0 -
num_last_reqs integral 32 'd1
num_last_rsps integral 32 'd1
m_wb_agent wb_agent - @2810
m_wb_drv wb_driver - @5712
rsp_port uvm_analysis_port - @5858
seq_item_port uvm_seq_item_pull_port - @5810
m_wb_mon wb_monitor - @5839
m_wb_seqr uvm_sequencer - @5136
rsp_export uvm_analysis_export - @5192
seq_item_export uvm_seq_item_pull_imp - @5732
arbitration_queue array 0 -
lock_queue array 0 -
num_last_reqs integral 32 'd1
num_last_rsps integral 32 'd1
--------------------------------------------------------------
UVM_INFO ./tb/my_pkg.sv(68) @ 0: uvm_test_top.m_top_env.m_virt_seq@@m_virt_seq [VSEQ] Start of virtual sequence
UVM_INFO ./tb/wb_agent.sv(63) @ 0: uvm_test_top.m_top_env.m_wb_agent.m_wb_seqr@@m_wb_reset_seq [RESET_SEQ] Starting wb_reset_seq
UVM_INFO ./tb/apb_agent.sv(52) @ 20000: uvm_test_top.m_top_env.m_apb_agent.m_apb_seqr@@m_apb_rw_seq [RW_SEQ] Starting apb_rw_seq
UVM_INFO ./tb/spi_agent.sv(74) @ 30000: uvm_test_top.m_top_env.m_spi_agent.m_spi_seqr@@m_spi_tx_seq [tx_SEQ] Starting spi_tx_seq
UVM_INFO ./tb/my_pkg.sv(75) @ 30000: uvm_test_top.m_top_env.m_virt_seq@@m_virt_seq [VSEQ] End of virtual sequence
UVM_INFO ./tb/my_pkg.sv(108) @ 30000: uvm_test_top [SHUT] Shutting down test ...
--- UVM Report catcher Summary ---
