benchmarks/readme.txt

   1 *************************************************************************
   2 Benchmarks for RISCV Processor
   3 -------------------------------------------------------------------------
   4
   5 The benchmarks make use of the RISCV C compiler toolchain. You will need
   6 to include a bmark.mk makefile fragment in each benchmark directory. The
   7 fragment should include the object files and a rule to actually link
   8 these object files into an executable. There are a couple important
   9 points to make about the toolchain.
  10
  11  + The toolchain sets the stack pointer to memory address 0x20000 so your
  12    main memory _must_ be larger than 0x20000 bytes or else the stack will
  13    get wrapped around and overwrite program data.
  14
  15  + The stack grows down from 0x20000 and your program is loaded at 0x1000.
  16    If you have a very large program and have lots of very big arrays
  17    declared on the stack your stack could overwrite your program. Be aware.
  18
  19  + You cannot use standard clib functions (like memcopy or strcat). You
  20    cannot use system calls and thus cannot use printf.
  21
  22  + You cannot access the simulated command line - ie you cannot use argc
  23    and argv within main.
  24
  25  + You may have to increase the timeout check in your test harness to
  26    allow longer programs to run (you can do this from the command line
  27    option +max-cycles with the standard test harness)
  28
  29  + The compiler loads the program at 0x1000. It does not insert exception
  30    setup code. So if you are careful with what C you use it will only
  31    generate code in the riscv lab1 subset. If you use multiplies, shorts,
  32    and chars it could generate mul, lh, and lb instructions. Be aware.
  33
  34  + You can write assembly in C - you need to do this to write tohost to 1
  35    to indicate when the benchmark is done. Look at the example
  36    benchmarks to see how this is done. You can find more information
  37    about how to write assembly in C here:
  38    http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html
  39
  40  + If you look at the example benchmarks you will see that I have two
  41    important macros HOST_DEBUG and VERIFY. Use HOST_DEBUG to compile the
  42    benchmark on your host workstation (ie use standard gcc on Athena/Linux
  43    box) and then debug the benchmark. Since you are using standard gcc you
  44    can use printf's to make sure that your benchmark actually works before
  45    trying it out on your RISCV processor.
  46
  47  + Debugging C compiled code on the RISCV processor is a real pain. It is
  48    hard to associate the assembly with the C code and there is no
  49    debugger. So if you encounter a bug in your processor when running a C
  50    benchmark you can try to debug it, but you might have better luck
  51    adding more assembly tests to your test suite.
  52
  53  + To avoid having the compiler try and use a global pointer (ie using
  54    register 28 to point to a space where small global variables are
  55    stored) you need to use the -G 0 command line option.