1. A Real-Time Program Trace CompressorUtilizing Double Move-to-Front MethodVladimir Uzelac, AleksandarMilenkovicThe University of Alabama in Huntsville DAC’09, July 26-31, 2009, San Francisco, California, USA Presenter: Shao-Jay Hou

2. Abstract • This paper introduces a new unobtrusive and cost-effective method for the capture and compression of program execution traces in real-time, which is based on a double move-to-front transformation. We explore its effectiveness and describe a cost-effective hardware implementation. The proposed trace compressor requires only 0.12 bits per instruction of trace port bandwidth, at the cost of 25K gates.

3. What’s the problem? • Continual growth in the complexity of SoC makes traditional approaches infeasible or impractical. • In-Circuit-Emulator (ICE) • Invasively ,have to stop the processor • Software approach • Use breakpoint • Software step-by-step debug waste too much time. • There are another tracing system, but the cost or the area is to high. • C.F.Kao’s LZ-based program trace.

4. My reaserch tree My thesis(ideal) The improve of tracer. The application of tracer. An Embedded Infrastructure of Debug and Trace Interface for the DSP Platform A Real-Time Program Trace Compressor Utilizing Double Move-to-Front Method

5. Related work This paper The program trace system for each embedded system processor Another program trace system and compression techniques For the experiment benchmark ARM ETM[1] AlteraNios II[2] Xilinx Microblaze[3] Lauterbach[4] [5-7] Mibench[8] Hardware architecture The basic MTF method and bzip compression To collect the symbols in system MTF[10] Bzip2[11] SimpleScalar[9] CAM[12]

6. Program Characteristics • For each instruction, there are two characteristics: • SA(staring address) • SL(stream length) • PC(program counter) • If the current PC is differ form the previous PC than the instruction length, the current instruction is the beginning of a new stream. • The unconditional direct branch we do not terminate the current stream because the address of the next instruction in sequence can be inferred directly from the binary.

7. Move-To-Front method • Some parameters in this method: • Ht(history table) • Input • Output • A easy example to explain it: • If the history table ht=[C,B,A] • The input is {AABC} • The output should be 2022

8. Program Characteristics and MTF

9. DMTF Method • Use two-level history table • Mtf1 • Mtf2 • The flow of DMTF:

10. DMTF Method(cont.) • The output bits of DMTF: • Mtf2.zhr=>mtf2 zero entry hit rate • Mtf2.ohr=>mtf2 non-zero entry hit rate • Mtf1.hr=>mtf1 hit rate • Mtf1.size=>mtf1 size • Mtf2. size=>mtf2 size

11. DMTF Method(cont.) • Am example of DMTF

12. DMTF Method(cont.) • The result of DMTF

13. Enhanced DMTF Method • Last-Value Predictor for Upper Address Bits: • Upper bits of SA in stream is rarely change during program execution • Use SA[31:20] as HLV • Zero Hit Trace Counters: • Mtf2 zero entry hit happen often • Use a counter to count and dynamically adjust the size of ZLC • Use a head bit “0”

14. Enhanced DMTF Method(cont.) • The block diagram of enhance DMTF trace format:

15. Enhanced DMTF Method(cont.) • bDMTF = basic DMTF • hDMTF = DMTF with HLV • eDMTF = enhance DMTF

16. DMTF Hardware Implemention • content addressable memory (CAM) • most-recently used (MRU) stack • the gates count of DMTF(192,4) is less then 24600

17. Conclusion • The paper present a double move-to-front method, and the compression ratio is between 82.7:1~29389:1(average is 268:1) and the bandwidth is 0.001 to 0.39 bits/instruction (average is 0.12) • And the hardware is area-save • Compare to C.F.Kao[5], the area is half.

18. My Conclusions • The paper give a good method in compression. • And the paper use many example to show the method how to run. • But the paper didn’t talk too much on how to experiment, and how to get the data.