Sequence, Sequence on the Wall, Who’s the Fairest of Them All?

Using SystemVerilog UVM Sequences for Fun and Profit

byRich Edelman and Raghu Ardeishar

Verification TechnologistsMentor Graphics

Questa Verification

Platform

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thefreedictionary.com/fairest • Who’s the fairest?• fair 1  (fâr)adj. fair·er, fair·est

– 1. Of pleasing appearance, especially because of a pure or fresh quality; comely.

– 2. a. Light in color, especially blond: fair hair.– b. Of light complexion: fair skin.– 3. Free of clouds or storms; clear and sunny: fair

skies.– 4. Free of blemishes or stains; clean and pure:

one's fair name.– 5. Promising; likely: We're in a fair way to

succeed.– 6. a. Having or exhibiting a disposition that is

free of favoritism or bias; impartial: a fair mediator.

– b. Just to all parties; equitable: a compromise that is fair to both factions.

– 7. Being in accordance with relative merit or significance: She wanted to receive her fair share of the proceeds.

– 8. Consistent with rules, logic, or ethics: a fair tactic.

– 9. Moderately good; acceptable or satisfactory: gave only a fair performance of the play; in fair health.

– 10. Superficially true or appealing; specious: Don't trust his fair promises.

– 11. Lawful to hunt or attack: fair game.– 12. Archaic Free of all obstacles.

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Overview - Smorgasbord• UVM Review

– Agents– Transactions – Sequences– Drivers

• Sequence API– start_item– finish_item– start– grab– priority

• Hierarchy/Constraints– Dice/roll– Words/Sentence

• Special Sequences– Task interface– Command line

(+SEQ=seqA)– Reading from a file– C code– Out-of-Order

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• Agent manages an interface• Driver wiggles the pins• Monitor monitors pin wiggles• Sequencer arbitrates access to the driver• Sequence generates transactions and sends them to

the driver

AGENT

Agents

DRVR

MON

SQRtrans

trans

SEQSEQSEQSEQSEQSEQ Interface:Pins & Pin Wiggles

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Fun Sequence/Sequencer/Driver• The sequence, sequencer and driver communicate

one transaction at a time with each other.1. The sequence creates (constructs) a transaction

and sends it to the driver.2. The sequencer arbitrates amongst multiple

sequences3. Finally the driver gets the transaction and acts on it

AGENT

DRVRSQR

transA

SEQA

SEQC

SEQB

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Transactions – here’s three• Transaction as a payload

class trans_c extends uvm_sequence_item; `uvm_object_utils(trans_c)

rand bit rw; rand bit[31:0] addr; rand bit[31:0] data; endclass

typedef enum { DICE1 = 1, DICE2, DICE3, DICE4, DICE5, DICE6} dice_t;

class dice_item extends uvm_sequence_item; `uvm_object_utils(dice_item)

rand dice_t value; ...endclass

class packet extends uvm_sequence_item; `uvm_object_utils(packet)

rand bit [7:0] som; rand bit [7:0] addr; rand bit [7:0] payload [8]; bit [7:0] checksum; rand bit [7:0] eom;

constraint val { som == '0; eom == '1; foreach (payload[i]) payload[i] inside {[0:100]}; }

function void post_randomize(); checksum = 0; foreach (payload[i]) checksum = f(checksum, payload[i]); endfunctionendclass

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Sequences• Sequences are functors

– a class wrapper around a body() task• A sequence can have two jobs

– Generate a sequence of transactions– Start other sequences …

class dice_item extends uvm_sequence_item; rand dice_t value; ...endclass

class roll_sequence extends uvm_sequence#(dice_item); rand int how_many; task body(); dice_item t; for(int i = 0; i < how_many; i++) begin t = dice_item::type_id::create(...); if (!t.randomize()) begin `uvm_fatal("SEQ", "Randomize failed") end start_item(t); finish_item(t); end endtaskendclass

AGENT

DRVRSQR

SEQA

SEQC

SEQB

createrandomizestart_itemfinish_item

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Sequences – “virtual sequences”• Start other sequences

class axx_basic_sequence extends uvm_sequence_base; `uvm_object_utils(axx_basic_sequence)

axx_env env;

task body(); abc_sequence seq1; xyz_sequence seq2, seq3;

seq1 = abc_sequence::type_id::create("seq1"); seq2 = xyz_sequence::type_id::create("seq2"); seq3 = xyz_sequence::type_id::create("seq3");

fork seq1.start(env.agent1.sequencer); seq2.start(env.agent2.sequencer); seq3.start(env.agent3.sequencer); join endtaskendclass

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Sequences with grab• Get exclusive use of the sequencer

class roll_sequence extends uvm_sequence#(dice_item); `uvm_object_utils(roll_sequence) rand int how_many; constraint val { how_many > 70; how_many < 100; } task body(); dice_item t; grab(); for(int i = 0; i < how_many; i++) begin t = dice_item::type_id::create($sformatf("t%0d", i)); if (!t.randomize()) begin `uvm_fatal("SEQ", "Randomize failed") end start_item(t); finish_item(t); end ungrab(); endtaskendclass

AGENT

DRVRSQR

SEQA

SEQC

SEQB

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Transactions with priority– Default priority is 100.– Higher numbers are better.– Don’t forget to change the sequencer mode

sqr.set_arbitration(SEQ_ARB_STRICT_FIFO);class roll_sequence extends uvm_sequence#(dice_item); `uvm_object_utils(roll_sequence) rand int how_many; constraint val { how_many > 70; how_many < 100; } task body(); dice_item t; for(int i = 0; i < how_many; i++) begin t = dice_item::type_id::create($sformatf("t%0d", i)); if (!t.randomize()) begin `uvm_fatal("SEQ", "Randomize failed") end start_item(t, 1000); finish_item(t); end endtaskendclass

AGENT

DRVRSQR

SEQA

SEQC

SEQB

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Driver• Driver handshake with the sequence

class driver extends uvm_driver#(dice_item); `uvm_component_utils(driver)

// Simple counter for each face seen int distribution[dice_t];

task run_phase(uvm_phase phase); forever begin dice_item t; seq_item_port.get_next_item(t); distribution[t.value]++; `uvm_info("DRVR", $sformatf(" Got %s [%p]", t.convert2string(), distribution), UVM_MEDIUM) // Send to BUS... seq_item_port.item_done(); end endtaskendclass

AGENT

DRVRSQR

SEQA

SEQC

SEQB

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Tasks Wrapping Sequences• Sequence wrapped with a simple task• Task does ‘seq.start(sequencer)’

task read(input bit [7:0] addr, output bit [7:0] data); read_seq seq; seq = read_seq::type_id::create("read",, get_full_name()); seq.addr = addr; seq.start(seqr); data = seq.data; endtask

class trans extends uvm_sequence_item; `uvm_object_utils(trans) rand bit rw; rand bit [7:0] addr; rand bit [7:0] data; ...endclass

class read_seq extends uvm_sequence#(trans); `uvm_object_utils(read_seq) rand bit [7:0] addr; // Input bit [7:0] data; // Output task body(); trans t; t = trans::type_id::create("t",, get_full_name()); t.rw = 1; t.addr = addr; start_item(t); finish_item(t); data = t.data; endtaskendclass

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Command line - +SEQ=<seqA>

task run_phase(uvm_phase phase); string sequence_name; uvm_object obj; simple_value_base_class seq; string list_of_sequences[$]; uvm_cmdline_processor clp;

clp = uvm_cmdline_processor::get_inst(); clp.get_arg_values("+SEQ=", list_of_sequences)

foreach (list_of_sequences[n]) begin sequence_name = list_of_sequences[n]; phase.raise_objection(this); obj = factory.create_object_by_name(sequence_name); if (obj == null) /* Handle Error */ if (!$cast(seq, obj)) /* Handle Error */ seq.env = env; seq.start(null); phase.drop_objection(this); endendtask

<SIM> +SEQ=seqA +SEQ=seqB

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Reading from a file - +FILE=<file>class read_sequence_from_file extends uvm_sequence#(value_item);

`uvm_object_utils(read_sequence_from_file)

task body(); int fd, count; string filenames[$], sequence_name; uvm_object obj; simple_value_base_class seq; uvm_cmdline_processor clp; clp = uvm_cmdline_processor::get_inst(); clp.get_arg_values("+FILE=", filenames) foreach (filenames[n]) begin fd = $fopen(filenames[n], "r"); while(!$feof(fd)) begin ret = $fscanf(fd, "%s %d", sequence_name, count); obj = factory.create_object_by_name(sequence_name); if (obj == null) /* Handle Error */ if (!$cast(seq, obj)) /* Handle Error */ if (!seq.randomize() with {seq.how_many == count;}) /* Handle Error */ seq.start(m_sequencer); end // while end // foreach endtaskendclass

sequences.txt:fibonacci_sequence 10triangle_sequence 20

<SIM> +FILE=sequences.txt +FILE=sequences2.txt

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DPI-C (bound)• Use C code to

– Get stimulus input– Get expected output– Scoreboard (checker)

interface my_interface(); import "DPI-C" context task c_calc(output int x); export "DPI-C" task intf_calling_back;

seq my_class_handle;

function void init(seq s); s.vif = interface::self(); my_class_handle = s; endfunction

task intf_calling_back(output int x); my_class_handle.class_calling_back(x); endtaskendinterface

class seq; virtual my_interface vif;

task class_calling_back(output int x); #10 x = id; endtask

task body(); int x; for(int i = 0; i < 5; i++) vif.c_calc(x); endtaskendclass

C Codeintc_calc(int *val) { int id; intf_calling_back(&id); printf("c_calc() Scope = %s\n", svGetNameFromScope(svGetScope())); *val = id++; return 0;}

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DRIVER

Out-of-Order – sequence/driver

SEQUENCEforever begin get_next_item(t); work_list.push(t); item_done();end

forever begin work_list.pop(t); t.item_really_started(); lookup[tag] = t; send t to BUSend

Execute

forever begin @(interrupt); t = lookup[tag]; t.resp = BUS.resp; resp_list.push(t);end

ISR

forever begin resp_list.pop(t); t.item_really_done();end

RSP

trans t;t = new(“t”);start_item(t);finish_item(t);

Run

DUT

t

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Out-of-Order – item_really_done

SEQtrans t;t = new(“t”);start_item(t);finish_item(t);

class trans ... bit item_really_done_e;

function item_really_done(); item_really_done_e = 1; endfunction ...endclass

t

DRIVER

forever begin get_next_item(t); work_list.push(t); item_done();end

forever begin resp_list.pop(t); t.item_really_done();end

RSP

Run

class my_sequence_base ...

function finish_item(trans t); super.finish_item(t); wait(t.item_really_done_e == 1); endfunction

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Summary

• Sequences are the way to write tests. • Just code that ...

– Starts other sequences– Sends transactions

• Sequences have an API• Randomized tests – constraints, layering• Directed tests, C code, files, command line• Building collections of sequences is a good idea• Glad to share source code. Some of it is in the

paper. Questions?rich_edelman@mentor.com

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BACKUP SLIDES

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Fun with Words• Encryption hardware – one word at a time

• Job of the Stimulus– Generating words– Generating four-letter-words– Sentences, Paragraphs, Chapters, …

• Use Constraints– Unique combinations– Distribution of letters

• Really Fun with Constraints – SV LRM Chapter 18 – only(!) 50 pages out of 1315

DUTword

mode

encrypted word

Hold the Presses! News Flash

Just released

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Transaction/Sequence Design• Transaction: a word

(data), an encryption mode and the result (secret_data)

• Sequence: create a word and send it.virtual class my_sequence extends uvm_sequence#(transaction);

`uvm_object_utils(my_sequence) rand byte data[];

task body(); transaction t; t = transaction::type_id::create("t"); start_item(t); if (!t.randomize()) `uvm_fatal("MSG", "Randomization failed") t.data = data; finish_item(t); `uvm_info("MSG", $sformatf("secret=%s", t.secret_data), UVM_MEDIUM) endtaskendclass

class transaction extends uvm_sequence_item; ... rand mode_t mode; // CLR or ROT13 rand byte data[]; string secret_data;endclass

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Four Letter Words - constraints• Inheritance• Sequence: Extends ‘my_sequence’. “IS-A”

– Randc data from the gadget ‘r’.– pre_randomize()– post_randomize()

• What is ‘r’?

class four_letter_words extends my_sequence; `uvm_object_utils(four_letter_words)

four_letter_words_randc r; function new(string name = “..."); super.new(name); r = new(); endfunction function void pre_randomize(); if (!(r.randomize())) `uvm_fatal(...) endfunction function void post_randomize(); data = r.sdata; endfunctionendclass

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The Gadget ‘r’

• Just a container which allows for randc to be used.• How to generate all the possible four letter words

with no repeats?– Randomize ‘value’– Convert ‘value’ to string sdata – Modulo 26 operations

class four_letter_words_randc; string sdata; randc int value; constraint val { value >= 0; value < 456976; }

function void post_randomize(); int v; sdata = " "; v = value; for(int i = 0; i < 4; i++) begin sdata[i] = (v%26) + "a"; v = v/26; end endfunction

Note to math people 26**4 = 456976

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Short Word• More…

– Inheritance– Constraints

class short_word_seq extends my_sequence; `uvm_object_utils(short_word_seq)

rand int length; constraint val_length { length >= 3; length <= 8; }

constraint val_data_length { data.size() == length; } constraint val_data { foreach (data[i]) { data[i] inside {["a":"z"]}; // 'a' to 'z'

if ( i == 0) // First letter of the word data[i] dist {"a" := 116, ... "z" := 01}; else data[i] dist {"a" := 81, ... "z" := 01}; } }endclass

class my_sequence extends ... `uvm_object_utils(my_sequence) rand byte data[];

task body(); transaction t; t = transaction::type_id::create("t"); start_item(t); if (!t.randomize()) `uvm_fatal(...) t.data = data; finish_item(t); endtaskendclass

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Sentence Seq• Sentence “HAS-A” seq

– it generates sequences and starts them.– 4 letter– Short word

• Paragraph• Chapter• Book

class sentence_seq extends uvm_sequence#(transaction); `uvm_object_utils(sentence_seq) rand int how_many; rand bit use_four_letter_word = 0; constraint val_how_many {how_many > 0; how_many < 200;} task body(); uvm_sequence_base seq; for(int i = 0; i < how_many; i++) begin if (use_four_letter_word) seq = four_letter_words::type_id::create(“..."); else seq = short_word_seq::type_id::create(“...");

if (!seq.randomize()) `uvm_fatal("SEQ", "Randomize failed")

seq.start(m_sequencer); end endtask

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Factory - Overrides– Type based override– Instance based override

class test extends uvm_test; `uvm_component_utils(test)

task run_phase(uvm_phase phase); n_packets seq1, seq2;

phase.raise_objection(this);

packet::type_id::set_type_override( packet_with_randc_addr::get_type);

packet::type_id::set_inst_override( big_packet::get_type(), "uvm_test_top.e1.sequencer.seq1.packet");

seq1=n_packets::type_id::create("seq1",,get_full_name()); seq2=n_packets::type_id::create("seq2",,get_full_name());

factory.print();...