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EmBounded Report on AbsInt’s Contributions

EmBounded Report on AbsInt’s Contributions. WCET Analyzer aiT. Input: Executable Specifications in AIS language Output now: Control-flow graph with WCET annotations Report file with addresses of memory accesses and WCET information Goal: Integration into Hume compiler.

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EmBounded Report on AbsInt’s Contributions

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  1. EmBoundedReport on AbsInt’s Contributions

  2. WCET Analyzer aiT • Input: • Executable • Specifications in AIS language • Output now: • Control-flow graph with WCET annotations • Report file with addresses of memory accesses and WCET information • Goal: Integration into Hume compiler

  3. Extension of aiT for M32 • Support of executables in .X30 format • Value analysis • Bounds for register-dependent loop instructions • Extension of the AIS specification language • First experiences with output of Hume compiler

  4. X30 Executables • Originally, aiT for M32 could only read .elf executables • Now it can also read .X30 executables • Data sections in .X30 executables are better marked than in .elf executables

  5. Value Analysis • Value analysis tries to find lower and upper bounds for the values in the registers and memory cells • Value analysis for M32 was implemented during the EmBounded project

  6. Usage of Value Analysis The results of value analysis are used to get • Addresses of memory accesses • Important in case of different memory areas with different access times • Infeasibility information • If conditions evaluate always to true or always to false, the other successor need not be analyzed further • Upper bounds for the iteration numbers of simple loops

  7. Looping Instructions • Certain M32 instructions perform a data-dependent loop when executed. • rmpa, sinb, smovb, smovf, sout, and sstr:the number of loop iterations is given by the contents of register R3. • Value analysis can find loop bounds for these instructions. • smovu and scmpu iterate through the memory till they find a zero-byte. • aiT does not determine the iteration counts for any of these two instructions. Hence, all these instructions require a user annotation.

  8. AIS Annotations Generally important annotations: • INSTRUCTION … CALLS …;INSTRUCTION … BRANCHES TO …; • LOOP ProgramPoint Qualifier Bounds ; • loop “R” + 10 bytes end max 10; • loop “R” + 2 loops begin exactly 20; • RECURSION "name" Bounds ; • recursion “_cmpPrim” max 8;

  9. Annotations specific to M32 • Memory map is fixed apart from • End of Internal RAM Block A starting at 0x000400:global "XXXXXX" = address ; • Beginning of Internal RAM Block B ending at 0xFFFFFF:global "YYYYYY" = address ; • Declaration of external bus areas:AREA FROM … TO … ACCESS TIME = …; • area from 0x80a000 to 0xcfffff access time = 3;

  10. Annotations specific to M32 (cont.) • For instructions performing data-dependent loops:INSTRUCTION … FEATURES transfer_count = … ; • instruction “R” + 10 bytes features transfer_count = 5; • Always necessary for smovu and scmpu that loop till a zero-byte is found. • Necessary for rmpa, sinb, smovb, smovf, sout, and sstr, which depend on R3, if value of R3 is not found by value analysis.

  11. Experiences with code from Hume Example: Simple Simon translated from Hume to C and then further to M32 • Globally complicated control flow • Setjmp/longjmp • Many annotations required (from compiler) • Recursion needing recursion bounds • _cmpPrim (compares two structures recursively) • _throwException  _mkTup  _throwException • _throwException  _setException  _mkCon  _throwE. • Many loops requiring loop bounds

  12. Experience with Small Snippets In presence ofsnippet "_throwException" is never executed; many routines can be analyzed: • _mkBool, _mkCon, _mkInt, _mkTup • _output, _setException, _setHeap, … Result: WCET under the assumption that no exceptions occur.

  13. To do now • How to compute global WCET

  14. email: info@AbsInt.com http://www.AbsInt.com

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