Failing to Fail: Achieving Success in Advanced Low Power Design using UPF

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Failing to Fail: Achieving Success in Advanced Low Power Design using UPF 1 Rick Koster, 2 John Redmond, and 3 Shreedhar Ramachandra 1 Mentor Graphics Corporation 2 Broadcom Corporation 3 Synopsys Inc. International Symposium on Low Power Electronics and Design

UPF Overview Rick Koster Mentor Graphics International Symposium on Low Power Electronics and Design

Agenda UPF Overview Low Power Management Concepts What is UPF Power Management Structures Power Management Behavior 3

Power Management Concepts Power Gating: Shutting off power to portions of the design (Power Domains) to eliminate leakage power consumption Multi Voltage Designs: Organizing the design into different voltage domains as a function of performance to minimize dynamic and static power consumption Voltage and Frequency Scaling Dynamically tune parts of the design to meet performance goals with minimum power Power Management requirements Isolation, Level Shifting, State Retention, Switching 4

What is UPF? An Evolving Standard Accellera UPF in 2007 (1.0) IEEE 1801-2009 UPF (2.0) IEEE 1801-2013 UPF (2.1) IEEE 1801A-2014 UPF (2.2) For Power Intent To define power management To minimize power consumption Through control of leakage Based upon TCL Tcl syntax and semantics Can be mixed with non-upf TCL And HDLs SystemVerilog, Verilog, VHDL For Verification Simulation or Emulation Static/Formal Verification And for Implementation Synthesis, DFT, P&R, etc. 5

Power Management Structures Power Domains Domain Interfaces (ISO/LS) Retention Supply Sets Supply Ports/Nets Power Switches 6

Power Domains A collection of instances that are treated as a group for power-management purposes. A Power domain exists within a logical scope UPF and HDL identifiers must be unique within the scope All UPF commands are executed within the current active scope A power domain can have associated with it isolation strategies, retention strategies and level shifter requirements 7

Power Domains create_power_domain DUT_PD include_scope create_power_domain C1_PD -elements {CPU1} create_power_domain C2_PD -elements {IP1 CPU2} C2_PD C1_PD DUT IP1 CPU 2 CPU1 Memory cache BUS/Fabric P1 P2 P3 IP2 Power CTRL DUT_PD 8

Supply Sets Represent a collection of supply nets that provide a power source. Consists of a set of up to 6 supply functions power, ground, nwell, pwell, deepnwell, deeppwell One supply net per (required) function Electrically complete model of a power distribution network in a domain: power, ground, etc. Power domains have a few predefined supply sets: primary, default_isolation, and default_retention Supply sets can be associated with one another to model supply connections abstractly Supply Nets Supply Set Main Functions power ground nwell pwell deepnwell deeppwell create_power_domain PD_u1 include scope create_power_domain PD_u11 elements {U1/U11} create_power_domain PD_u12 elements {U1/U12} P U11 U1 I R P I R U12 L1 L2 L3 L4 L5 P I R 9

Domain Interfaces Power gating can cause electrical and logical problems to adjacent domains. Isolation is used to prevent these problems. Isolation cell: An instance that passes logic values during normal mode operation and clamps its output to some specified logic value when a control signal is asserted. Multi voltage designs can also experience problems Level shifters are used to maintain signal integrity. Level shifter cell: An instance that translates signal values from an input voltage swing to a different output voltage swing. 10

Retention/Repeaters Device operation may require the use of flip flops or memories that preserve state during a domain s power down. Preserving state is achieve through the use of UPF retention. Retention: Enhanced functionality associated with selected sequential elements or a memory such that memory values can be preserved during the powerdown state of the primary supplies. 11

Supply Ports/Nets Power Domain supply sets consist of supply nets that eventually are driven by supply ports Supply ports and nets are defined as objects of supply_net_type UPF package defines supply_net_type as: typedef enum (OFF=0,UNDETERMINED, PARTIAL_ON, FULL_ON) state typedef struct packed { state state; int voltage; // voltage in microvolts } supply_net_type; 12

Power Switches A power switch is a design element that conditionally connects input supply nets to an output supply net A UPF switch can be on or off or partially on The state of the switch is set by Boolean functions of the control ports Match = input voltage propagates to output (on) No Match = output port disabled (off) Either power or ground can be switched 13

set_design_top U1 create_power_domain PD_u1 include scope create_power_domain PD_u11 elements {U1/U11} create_power_domain PD_u12 elements {U1/U12} create_supply_net sw1_out_net create_power_switch SW1 \ -domain PD_u1 \ -output_supply_port {swout sw1_out_net} \ -input_supply_port {swin PD_u1.primary.power} \ -control_port {swctrl swctl1} \ -on_state {SWon swin swctrl} \ -off_state {SWoff!swctrl} create_supply_set sw1_ss \ -function {power sw1_out_net} \ -function {ground PD_u1.primary.ground} associate_supply_set sw1_ss -handle PD_u11.primary associate_supply_set PD_u1.primary \ -handle PD_u11.default_retention associate_supply_set PD_u1.primary \ -handle PD_u11.default_isolation set_isolation iso_pd_u11 domain PD_u11 \ -location self clamp_value {1} \ -applies_to outputs set_retention ret_pd_u11 domain PD_u11 \ -elements {U11/ret1} \ -save_signal {U11/ret_n} high \ -restore_signal {U11/ret_n low} R UPF Structure Command example SW1 P I I P R U11 ISO U1 U12 RET1 L2 L3 L4 RET5 P I R 14

create_supply_net sw2_out_net create_power_switch SW2 \ -domain PD_u2 \ -output_supply_port {swout sw2_out_net} \ -input_supply_port {swin PD_u1.primary.power} \ -control_port {swctrl swctl2} \ -on_state {SWon swin swctrl} \ -off_state {SWoff!swctrl} create_supply_set sw2_ss \ -function {power sw2_out_net} \ -function {ground PD_u1.primary.ground} associate_supply_set sw2_ss -handle PD_u12.primary associate_supply_set PD_u1.primary \ -handle PD_u12.default_retention associate_supply_set PD_u1.primary \ -handle PD_u12.default_isolation set_isolation iso_pd_u12 domain PD_u11 \ -location self clamp_value {0} \ -applies_to outputs set_retention ret_pd_u12 domain PD_u11 \ -elements {U12/ret1} \ -save_signal {U12/ret_n posedge} -restore_signal {U12/ret_n negedge} R UPF Structure Command example SW1 P I I P R U11 ISO U1 U12 P ISO I SW2 R RET1 L2 L3 L4 RET5 15

Behavior Supply set Power States Simstates Power Domain States 16

Supply Sets Power States The power states of a supply set describe the expected combination of states of the supply nets in the supply set The state can be defined by a logic expression and may include supply expression State holds when logic expression is TRUE A power state defines the legal values of supply set functions when in that state Also may include a simstate add_power_state PdA.primary -state GO_MODE { logic_expr {SW_ON } simstate NORMAL -supply_expr {{power == {FULL_ON 0.8}} && {ground == {FULL_ON, 0}} && {nwell == {FULL_ON 0.8}}} -state OFF_MODE { logic_expr {!SW_ON} simstate CORRUPT} -supply_expr {power == {OFF}} 17

Simstates Simstate defines precise simulation semantics in this state. That is, the expected behavior of the cells connected to this supply set. CORRUPT Combinational outputs corrupted Sequential state/outputs corrupted NORMAL Combinational logic functions normally Sequential logic functions normally Both operate with characterized timing CORRUPT_ON_ACTIVITY Combinational outputs maintained as long as inputs are stable Sequential state/outputs corrupted CORRUPT_ON_CHANGE Combinational outputs maintained as long as outputs are stable Sequential state/outputs corrupted CORRUPT_STATE_ON_ACTIVITY Combinational logic functions normally Sequential state/outputs maintained as long as inputs are stable CORRUPT_STATE_ON_CHANGE Combinational logic functions normally Sequential state/outputs maintained as long as outputs are stable 18

Power States of a Power Domain A power domain is designed to have a set of allowable states in which it can operate. The domain power states describe the allowable set of states for a domain. Each state is defined by a logic expression Logic expressions can be created with: States of supply_sets Logic port and net values Subdomain power states Interval Functions 19

Attributes Characteristics of a port or design element Used to identify power supplies for ports set_port_attributes -ports Out1 -attribute \ {UPF_related_power_port VDD } Used to specify constraints for IP usage: set_port_attributes ports {logic_port} attribute \ {UPF_clamp_value 1 } Used to specify structure and behavior set_design_attributes elements ALU1 attribute \ {UPF_is_leaf TRUE} set_design_attributes elements ALU1 attribute \ {UPF_retention required} 20

UPF captures power intent of a design Power gating, multiple voltage, dynamic voltage and frequency scaling, isolation, retention, level shifting UPF works with HDL Summary Verilog, VHDL and SystemVerilog UPF guides verification and implementation UPF is an evolving standard Accellera UPF in 2007 (1.0) IEEE 1801-2009 UPF (2.0) IEEE 1801-2013 UPF (2.1) IEEE 1801a-2014 UPF (2.2) 21

UPF For ASIC Design John Redmond * Broadcom Corporation * Slides contributed by Sushma Honnavara-Prasad International Symposium on Low Power Electronics and Design

Introduction How power intent is realized in silicon Leaf Cells and macro models Soft IP modeling Successive refinement Constraints, configuration, implementation SoC integration Agenda Hierarchical UPF composition Supply network construction System power states and transitions 23

Power intent is captured through UPF, HDL and Library UPF realizes: Supply network specification power/ground/nwell/pwell/deepnwell/deeppwell Macro and IO power connectivity On-chip power switch specification Power domain specification Introduction Identify a standard cell region, supply availability in a region Strategies and their implementation Dictates inference of isolation cells, level shifters, repeaters and retention cells Leaf cell/macros need models to identify supply pins Liberty (.lib) provides UPF attributes LEF identifies power/ground/signal pins 1801-2013 enables cell and macro modeling 24

Leaf Cells An instance that has no descendants or has UPF_is_leaf_cell attribute on it Typically refer to standard cells HDL simulation model UPF low power cells specification Liberty implementation LEF physical design Attributes of interest supply vs signal pins supply properties cell attributes pin attributes function attributes UPF specifies either explicit, implicit or automatic supply connectivity to leaf cells top module sub module sub module sub module leaf cell (INVX1) {... pg_pin (VDD) {... pg_pin (VSS) {... 25

Macros Also called IPs, a piece of functionality optimized for power/area/performance Soft macros handed off as synthesizable HDL (technology agnostic) Hard macros handed off as LEF/GDS (technology specific) Also a leaf cell UPF_is_macro_cell attribute allows the model to be recognized as part of lower boundary of the domain containing the instance Can be modeled as: UPF Power Models Liberty models Example of a hard macro Embedded SRAM 26

UPF Power models Regular UPF commands enclosed between being_power_model and end_power_model Applied on an IP instance using apply_power_model command Models power states, port attributes, isolation etc. Liberty models Pin, supply and cell based attributes available switch_pin, pg_pin, is_macro_cell etc. Verilog simulation models IP Modeling Model supply as logic functions 27

Successive Refinement IP provider IP Source IP licensee Integrator Technology specific implementation 28

Constraints Identify "atomic" power domains in the design Indivisible, but can be merged during implementation create_power_domain PD_IP1 elements { u_inst_ip1 } -atomic Identify state elements to be retained during power down Type of retention flop, controls not specified set_retention_elements PD_IP1_ret_elem elements $ip1_elem_list $ip1_elem_list = list of elements that need to be retained in PD_IP1 Identify isolation clamp values on ports Isolation controls not specified set_port_attributes elements $ip1_elem_list -applies_to outputs \ -clamp_value 0 Specify legal power states and sequencing between them Supply ports, actual voltages not specified add_power_state PD_IP1 domain \ -state { nom -logic_expr { (ss_ip1 == nom) && {ss_ip2!= off) } 29

Uniquify/finalize power domains based on RTL configuration Number of instances generated determined by RTL parameters Merge power domains create_composite_domains PD_IP subdomains { PD_IP1 PD_IP2 } Create the required power-management ports (pwr/iso/ret) create_logic_port pwronin direction in create_logic_port iso Configuration direction in Create isolation strategies to fulfill isolation requirements set_isolation sw_iso_c0 domain PD_IP -applies_to outputs \ -clamp_value 0 isolation_signal iso \ -isolation_sense high location self Create retention strategies to fulfill retention requirements set_retention sw_ret domain PD_IP elements $ip1_elem_list \ retention_condition { ret } Update power states and power transitions add_power_state PD_IP domain update \ -state { nom -logic_expr { pwronin } } 30

Create supply ports and nets create_supply_port VDD1 direction in create_supply_net VSS domain PD_SUB1 -reuse Update supply set functions create_supply_set ss_ip1 update function {power VDD1} \ -function {ground VSS} Update power states with supply values add_power_state ss_ip1 update supply \ -state {nom -supply_expr {(power == {FULL_ON 0.9}) && (ground == {FULL_ON 0})} Create power-switches create_power_switch PSW_PD_IP domain PD_IP \ -input_supply_port { in_vdd VDDB } \ -output_supply_port { out_vdd VDD } \ -control_port { sw_ctrl pwronin } \ -on_state { full_on in_vdd {sw_ctrl} } \ -off_state { full_off {!sw_ctrl} } Map strategies to technology specific library cells use_interface_cell sw_low -strategy sw_iso_c0 -domain PD_IP \ -lib_cells $list_lib_cells Implementation 31

A typical SoC contains: Hard IP (fully implemented macros) Soft IP (HDL integrated into top level) Analog/mixed signal macros IO pads Considerations: Bottom up or top down implementation IP reuse Verification complexity System level power states SoC Integration 32

Partition design UPF into sub-module UPF load_upf $env(upf_path)/module1/upf/module1.upf \ -scope core_inst/module1_inst load_upf $env(upf_path)/module2/upf/module2.upf \ -scope core_inst/module2_inst Top level UPF can be split into multiple files for readability source $env(upf_path)/top_level/upf/create_supply_ports.upf source $env(upf_path)/top_level/upf/create_supply_sets.upf Complete supply connectivity to macros and sub-modules set pll_inst_list [find_objects. -pattern *u_pll* -object_type inst \ -leaf_only -transitive] foreach inst $pll_inst_list { } Hierarchical Composition connect_supply_net 1p8ss.power -ports $inst/avdd1p8 connect_supply_net 1p8ss.ground -ports $inst/avss ISO/LS at top level or inside blocks For large number of domains, move complexity into blocks 33

Model all primary supplies and on chip supplies create_supply_port VDD1P8 create_supply_net VDD_LDO connect_supply_net VDD_LDO ports u_ldo_inst/vddout Model all the power/ground pads and padring connectivity Power pads and IO ring power connectivity set pad_inst_list [find_objects. -pattern *PAD_SEG2_inst* \ -object_type inst -leaf_only -transitive] foreach pad_inst $pad_inst_list { } Supply Network Construction connect_supply_net pad_ring_vss -ports $pad_inst/vssp Reduce number of supply ports/nets/sets using equivalences Several IO supplies are functionally equivalent Some supplies might be connected at package level/off-chip set_equivalent function_only { AVDD VDD1P8 pad_ana_vdd } set_equivalent function_only { AVSS pad_avss ana_vss VSS dig_vss } 34

Supply States Describe supply states of supply sets using supply_expr Describe simstate for a supply state add_power_state var1ss -supply \ -state { nom -supply_expr { (power == {FULL_ON 0.8}) && (ground == {FULL_ON 0}) && \ (nwell == {FULL_ON 0.8}) } \ -state { turbo -supply_expr { (power == {FULL_ON 0.9}) && (ground == {FULL_ON 0}) && \ (nwell == {FULL_ON 0.9}) } \ -state { offmode -supply_expr { (power == {OFF}) && (ground == {FULL_ON 0}) && \ (nwell == {OFF}) -simstate CORRUPT} 35

System Power States Describe system states for the top domain add_power_state PD_TOP domain... Expressed using logic_expr with either: Supply set states Power domain states The number of state combinations could be large Simplify by identifying illegal states Identify equivalent supplies Apply state reduction When all legal power states are defined, the power state table can be marked complete All remaining undefined states are rendered illegal 36

System Power State Reduction 37

System Power States add_power_state PD_TOP -domain \ -state { on \ -logic_expr { (var1ss!= offmode) && (var2ss!= offmode) && \ (var3ss == nom var3ss==turbo) && (var4ss!= offmode)} } \ -state { var1off \ -logic_expr { (var1ss == offmode) && (var3ss == nom var3ss==turbo) && \ (var4ss!= offmode)} } \ -state { var2off \ -logic_expr { (var1ss!= offmode) && (var2ss == offmode) && \ (var3ss == nom var3ss==turbo) && (var4ss!= offmode)} } \ -state { var4off \ -logic_expr { (var1ss == offmode) && (var3ss == nom var3ss==turbo) && \ (var4ss == offmode)} } \ -state { alloff \ -logic_expr { (var1ss == offmode) && (var2ss == offmode) && \ (var3ss == nom var3ss==turbo) && (var4ss == offmode)} } 38

Power State Transitions Describe state transitions, both legal and illegal Used to validate power state changes in simulation describe_state_transition i1 -object PD_TOP -from {alloff} -to {on} illegal describe_state_transition i2 -object PD_TOP -from {on} -to {alloff} illegal describe_state_transition t1 object PD_TOP -from {on} to {var1off var2off} describe_state_transition t2 object PD_TOP -from {var1off} to {on var2off var4off} 39

Summary Power intent is augmented based on design phase by a process of successive refinement Soft IP providers deliver UPF constraints, IP integrator configures it to deliver technology agnostic UPF Implementation UPF commands allow for technology specific design SoC UPF is hierarchically composed of sub-module UPF SoC supplies, supply states, power states and state transitions can be modeled in UPF 40

Power Aware Verification Shreedhar Ramachandra Synopsys Inc. International Symposium on Low Power Electronics and Design

Agenda Introduction Power Aware Static Verification Power Aware Simulation Power Aware Coverage 42

Introduction Traditional verification does not involve voltage/power transitions Power Aware Verification Verify the complex power management schemes Make sure that the design can successfully function in all the power states for which it is designed Power related bugs Structural Control Sequencing Power Management Architecture 43

Static Verification Static Verification Does not involve time domain Power Aware Static Verification Check for correctness and completeness of the power intent Check consistency between power intent and implemented design HDL (DUT) Liberty (.lib) UPF Static Verification Tool (Performs Analysis) Reports 44

Static Verification: Power State Analysis VAO VCORE VMEM1 VMEM2 St1 1.2 0.8 0.8 0.8 St2 1.2 0.8 0.8 OFF St3 0.8 0.8 OFF OFF St4 0.8 OFF OFF OFF St5 OFF OFF OFF OFF ISO requirement Find OFF->ON paths, which contribute to leakage power LS requirement Find paths where there is voltage difference between source and sink 45

ISO Analysis (RTL) PDCORE VCORE (0.8) PDMEM2 VMEM2 (OFF) Redundant ISO Strategy Missing ISO Strategy PDMEM1 VMEM1 (OFF / 0.8) Missing ISO Strategy Isolation strategy is required on OFF->ON Paths Redundant ISO Strategy No state where source is OFF and sink is ON 46

LS Analysis (RTL) PDCORE VCORE (0.8) PDAO VAO(1.2) Redundant LS Strategy Missing LS Strategy PDMEM1 VMEM1 (OFF / 0.8) Missing LS Strategy Driver and receivers operate at different voltages Redundant LS Strategy No state where there is a voltage difference 47

Static Verification (RTL) PDMEM1 (OFF) VCORE PDCORE Control signals driven from domain that could be shutdown when the receiving logic is ON Driver supply of the control signals needs to be at least as ON as the supply of the receiving logic 48

ISO Supply ISO Supply OK PDMEM1 VMEM1 (OFF) PDMEM2 VMEM2 (OFF) ISO Supply Incorrect VCORE / VAO VMEM1 / VMEM2 PDCORE VCORE(0.8) Incorrect ISO supply ISO supply needs to be at least as ON as the receiving logic 49

ISO Control Connectivity Clamp Value PDMEM1 VMEM1 (OFF) Series of INV and/or BUF PDCORE VCORE(0.8) POWER MANAGER Verify ISO cell type, control connectivity and polarity Compare ISO strategy in UPF to actual ISO cells in the netlist 50

Always ON Buffering VMEM1 VCORE VCORE PDMEM1 VMEM1 (OFF) VAO Incorrect Supply PDCORE VCORE(0.8) POWER MANAGER Buffering Always ON buffers on feed-through paths need to use the proper supply 51

Power Aware Simulation (RTL) Functional Simulation Doesn t take into account the Power related effects Power Aware Simulation Simulates the effects due to Power related changes Catch Control Sequence and Architectural bugs HDL (DUT) Libraries (.v,.sv,.vhd,.lib) Power aware Testbench UPF Power Aware Simulator Waveform Reports Coverage 52

Power Aware Simulation (RTL) Ctrl VMEM1 X X X Ctrl PDCORE X X PDMEM1 Simulation of Supply Network Shutdown Corruption OFF domain propagates X values in simulation Virtual ISO insertion 53

Power Aware Testbench Modeling off-chip supplies VCORE Power Aware Testbench VAO module testbench; initial begin UPF::supply_on( VCORE, 0.8); UPF::supply_on( VAO, 1.2); UPF::supply_off( VCORE ); end 54

Retention Simulation (RTL) VDD VDDB VDD SAVE RESTORE VDD RR VDDB VDD RR Partial Retention Have you retained enough to get back to your original state? Have you retained more than required? 55

Power Aware Simulation (RTL) SAVE ISO_EN PWR_EN VDD RESTORE ISO control Enable before Power OFF and disable after Power ON Retention Save & Restore signal sequencing 56

Power Switch ACK ISO_EN PWR_EN VDD ACK ack delay Power switch ACK signal used to determine when the domain has been powered up The domain can then be reset and isolation disabled Delay modeled using ack_delay ack delay 57

Power Aware Coverage Functional coverage only addresses the design functionality without the effects of Power Power Aware coverage needs to address the aspects of Power Coverage of System Power States Power states that a system is designed for need to be covered by the simulation vectors Coverage of Transitions All legal transitions need to be covered Negative tests to cover illegal transitions ensure the system doesn t behave undeterministically 58

Conclusion Most of todays SOCs have Low Power. Power Aware verification at all design stages (RTL, Implemented netlist and PG netlist) is a must to ensure silicon success. Power Aware Static verification is required to catch basic power related bugs quickly without having any test scenarios. Power Aware simulation is required to catch control sequence related bugs using power aware testbench. Power Aware coverage ensures that all Power related scenarios have been covered. 59

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