Synchron'2008 Funchal Giovanni

Components and abstraction levels for system-on-chip Giovanni Funchal STMicroelectronics Verimag Synchron’2008

Introduction Simulation mechanics In practice Contributions Future work Imagine a system… Display USB FM radio PAL/NTSC TV-out Internet radio, podcasts 16Gb Flash Browser 256Mb RAM WLAN RF MPEG4 5Mp camera Bluetooth Internet 2Mp camera WCDMA, GSM MP3 E-mail MMS/SMS Java Operating Maps System GPS Microphone Keypad Battery Giovanni Funchal Components and abstraction levels for system-on-chip 2

Introduction Simulation mechanics In practice Contributions Future work …-on-chip STMicroelectronics Nokia N96 Nomadik STn8815 Giovanni Funchal Components and abstraction levels for system-on-chip 3

Introduction Simulation mechanics In practice Contributions Future work Design flow RTL model Giovanni Funchal Components and abstraction levels for system-on-chip 4

Introduction Simulation mechanics In practice Contributions Future work Register transfer level Precise description of hardware Synchronous, deterministic Giovanni Funchal Components and abstraction levels for system-on-chip 5

Introduction Simulation mechanics In practice Contributions Future work Design flow RTL model Fabrication Giovanni Funchal Components and abstraction levels for system-on-chip 6

Introduction Simulation mechanics In practice Contributions Future work Design flow Software RTL model Fabrication Giovanni Funchal Components and abstraction levels for system-on-chip 7

Introduction Simulation mechanics In practice Contributions Future work Design flow Too late! Software RTL model Fabrication Giovanni Funchal Components and abstraction levels for system-on-chip 8

Introduction Simulation mechanics In practice Contributions Future work Design flow Software RTL model Fabrication Giovanni Funchal Components and abstraction levels for system-on-chip 9

Introduction Simulation mechanics In practice Contributions Future work Design flow Software Simulator RTL model Fabrication Giovanni Funchal Components and abstraction levels for system-on-chip 10

Introduction Simulation mechanics In practice Contributions Future work Design flow Too slow! Software Simulator RTL model Fabrication Giovanni Funchal Components and abstraction levels for system-on-chip 11

Introduction Simulation mechanics In practice Contributions Future work Design flow Simpler, faster Software TLM model Simulator RTL model Fabrication Giovanni Funchal Components and abstraction levels for system-on-chip 12

Introduction Simulation mechanics In practice Contributions Future work Abstraction levels TLM models • Early (sw dev) • Less precise • Fast RTL models • Late (hw fab) • Precise • Slow Giovanni Funchal Components and abstraction levels for system-on-chip 13

Introduction Simulation mechanics In practice Contributions Future work Transaction level modeling Abstract transfers of data Asynchronous, non-deterministic Giovanni Funchal Components and abstraction levels for system-on-chip 14

Introduction Simulation mechanics In practice Contributions Future work Components Component Target port Initiator port Data interface Interrupt interf. Giovanni Funchal Components and abstraction levels for system-on-chip 16

Introduction Simulation mechanics In practice Contributions Future work Components What’s inside? Giovanni Funchal Components and abstraction levels for system-on-chip 17

Introduction Simulation mechanics In practice Contributions Future work SystemC • Processes (C++ code) Ready Running Waiting Giovanni Funchal Components and abstraction levels for system-on-chip 18

Introduction Simulation mechanics In practice Contributions Future work SystemC • Processes (C++ code) • Events Ready Running Waiting Giovanni Funchal Components and abstraction levels for system-on-chip 19

Introduction Simulation mechanics In practice Contributions Future work SystemC • Processes (C++ code) • Events • Scheduler Ready Running Waiting Giovanni Funchal Components and abstraction levels for system-on-chip 20

Introduction Simulation mechanics In practice Contributions Future work SystemC • Processes (C++ code) – wait() • Events • Scheduler Ready Running wait() Waiting Giovanni Funchal Components and abstraction levels for system-on-chip 21

Introduction Simulation mechanics In practice Contributions Future work Transactions in SystemC void irq() { port.irq(); … } Giovanni Funchal Components and abstraction levels for system-on-chip 22

Introduction Simulation mechanics In practice Contributions Future work Transactions in SystemC void irq() { port.irq(); … } Interface function calls Giovanni Funchal Components and abstraction levels for system-on-chip 23

Introduction Simulation mechanics In practice Contributions Future work An example Video Display decoder controller Memory Giovanni Funchal Components and abstraction levels for system-on-chip 24

Introduction Simulation mechanics In practice Contributions Future work Decoder: Display: decode(image); do { write(mem, image); x = read(flag); write(flag, true); } while(!x); wait(irq); img = read(mem); display(img); irq(); Giovanni Funchal Components and abstraction levels for system-on-chip 25

Introduction Simulation mechanics In practice Contributions Future work yield() • Like “wait()” but without saying what it is waiting for • The scheduler may choose the same process again Giovanni Funchal Components and abstraction levels for system-on-chip 31

Introduction Simulation mechanics In practice Contributions Future work Decoder: Display: decode(image); do { write(mem, image); yield(); write(flag, true); x = read(flag); wait(irq); yield(); } while(!x); img = read(mem); display(img); irq(); Giovanni Funchal Components and abstraction levels for system-on-chip 32

Introduction Simulation mechanics In practice Contributions Future work Decoder: Display: decode(image); do { write(mem, image); yield(); write(flag, true); x = read(flag); wait(irq); } while(!x); img = read(mem); display(img); irq(); Giovanni Funchal Components and abstraction levels for system-on-chip 33

Introduction Simulation mechanics In practice Contributions Future work Observations • “yield()” 1. Avoids livelocks by possibly giving other processes a chance to run 2. Finds bugs (next slides) Giovanni Funchal Components and abstraction levels for system-on-chip 37

Introduction Simulation mechanics In practice Contributions Future work Decoder: Display: decode(image); do { write(flag, true); yield(); write(mem, image); x = read(flag); wait(irq); } while(!x); img = read(mem); display(img); irq(); Giovanni Funchal Components and abstraction levels for system-on-chip 39

Introduction Simulation mechanics In practice Contributions Future work Design flow Software TLM model Simulator Software RTL model Fabrication Giovanni Funchal Components and abstraction levels for system-on-chip 40

Introduction Simulation mechanics In practice Contributions Future work Decoder: Display: decode(image); do { write(flag, true); yield(); yield(); x = read(flag); write(mem, image); } while(!x); wait(irq); img = read(mem); display(img); irq(); Giovanni Funchal Components and abstraction levels for system-on-chip 41

Introduction Simulation mechanics In practice Contributions Future work Decoder: Display: decode(image); do { write(mem, image); x = read(flag); yield(); yield(); write(flag, true); } while(!x); wait(irq); img = read(mem); display(img); yield(); irq(); Giovanni Funchal Components and abstraction levels for system-on-chip 42

Introduction Simulation mechanics In practice Contributions Future work Conclusions • A minimum amount of yielding makes a certain platform work • A bit more is needed to – make any platform work – finding bugs • Essential for component based approach! Giovanni Funchal Components and abstraction levels for system-on-chip 43

Introduction Simulation mechanics In practice Contributions Future work Approaches at ST • TAC1 – yield() between any two accesses – Poor performance Giovanni Funchal Components and abstraction levels for system-on-chip 44

Introduction Simulation mechanics In practice Contributions Future work Approaches at ST • TAC2 – Tag addresses “synchro” ( ) or “data” – yield() after any “synchro” – Very good performance Giovanni Funchal Components and abstraction levels for system-on-chip 45

Introduction Simulation mechanics In practice Contributions Future work Decoder: Display: decode(image); do { write(mem, image); x = read(flag); write(flag, true); yield(); yield(); } while(!x); wait(irq); img = read(mem); display(img); irq(); Giovanni Funchal Components and abstraction levels for system-on-chip 47

Introduction Simulation mechanics In practice Contributions Future work Decoder: Display: decode(image); do { write(mem, image); x = read(flag); yield(); yield(); write(flag, true); } while(!x); yield(); img = read(mem); wait(irq); display(img); yield(); irq(); Giovanni Funchal Components and abstraction levels for system-on-chip 48

Introduction Simulation mechanics In practice Contributions Future work State-of-the-art • TAC2.5 – Experimental results by Jérôme Cornet – Tag addresses “synchro” ( ) or “data” – yield() • before and after any “synchro” • before irq’s Giovanni Funchal Components and abstraction levels for system-on-chip 49

Introduction Simulation mechanics In practice Contributions Future work Decoder: Display: decode(image); do { write(mem, image); yield(); yield(); x = read(flag); write(flag, true); yield(); yield(); } while(!x); wait(irq); img = read(mem); display(img); yield(); irq(); Giovanni Funchal Components and abstraction levels for system-on-chip 51

Introduction Simulation mechanics In practice Contributions Future work Memory consistency contracts • Contract between processor and software in a multiprocessor system – Assume: software follows guidelines – Guarantee: memory stays consistent • Cache flushes, out-of-order execution,… Giovanni Funchal Components and abstraction levels for system-on-chip 52

Introduction Simulation mechanics In practice Contributions Future work Memory consistency contracts • Guidelines: access data synchro Giovanni Funchal Components and abstraction levels for system-on-chip 53

Introduction Simulation mechanics In practice Contributions Future work Memory consistency contracts • Guidelines: access data synchro non-competing competing release acquire Giovanni Funchal Components and abstraction levels for system-on-chip 54

Introduction Simulation mechanics In practice Contributions Future work Design flow Seen as specification TLM model Valid implementation? RTL model Fabrication Giovanni Funchal Components and abstraction levels for system-on-chip 55

Introduction Simulation mechanics In practice Contributions Future work From TLM… write write mem flag ... true read read read read flag flag flag mem irq false false true ... Giovanni Funchal Components and abstraction levels for system-on-chip 56

Introduction Simulation mechanics In practice Contributions Future work …to RTL write write write mem mem flag ... ... true read read read read read flag flag flag mem mem irq false false true ... ... Giovanni Funchal Components and abstraction levels for system-on-chip 57

Introduction Simulation mechanics In practice Contributions Future work …to RTL write mem ... write write mem flag ... true read read read read flag flag flag mem irq false false true ... read mem ... Giovanni Funchal Components and abstraction levels for system-on-chip 58

Introduction Simulation mechanics In practice Contributions Future work And from RTL… • “happens-before” partial-order write mem ... write write mem flag ... true read read read read flag flag flag mem irq false false true ... read mem ... Giovanni Funchal Components and abstraction levels for system-on-chip 59

Introduction Simulation mechanics In practice Contributions Future work Back to TLM… write write mem flag ... true read read read read flag flag flag mem irq false false true ... Giovanni Funchal Components and abstraction levels for system-on-chip 60

Introduction Simulation mechanics In practice Contributions Future work Understand yield • Link with “happens-before” partial-order Decoder: Display: decode(image); do { write(mem, image); x = read(flag); write(flag, true); } while(!x); wait(irq); img = read(mem); display(img); irq(); Giovanni Funchal Components and abstraction levels for system-on-chip 61

Introduction Simulation mechanics In practice Contributions Future work Future work • Import memory consistency contracts to TLM – Formal justification for “synchro” – Better understanding helps placing tags • Multi abstraction-level components – “happens-before” order must be maintained by valid implementations (contracts?) Giovanni Funchal Components and abstraction levels for system-on-chip 62

Synchron'2008 Funchal Giovanni

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