Reading from STDIN for simulation

Discussion in 'VHDL' started by gthorpe, Jul 12, 2005.

  1. gthorpe

    gthorpe Guest


    I would like to pipe (UNIX pipe) inputs into my simulation e.g.:

    'gunzip -c inputs.gz | ncsim -batch testbench'

    where the testbench reads in lines of input:

    while not endfile(input) loop
    readline(F=>input, L=>line);
    gthorpe, Jul 12, 2005
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  2. gthorpe

    Hubble Guest

    Looks like ncsim does some weird ioctls when it detects that you do not
    read from an ordinary file, like FIOASYNC etc. and does not handle the
    pipe case correctly. If there is no complete data line, the simulator
    stop instead of waiting :-(.

    You can try to use trace or strace commands to detect what is going on.
    These will print the system calls to stderr.

    However, without source there seems to be little chance to correct your

    Hubble, Jul 13, 2005
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  3. gthorpe

    gthorpe Guest


    Thanks, I was wondering if I was doing something wrong. It seems that the
    simulator is in fact trying to perform seeks on the pipe, which fails. For
    standard input, it polls unsuccessfully.

    Interestingly, the seeks would not move the file pointer anyway:

    lseek(10, 0, SEEK_CUR);

    Where 10 is the fd of the pipe. It is trying to set the pointer to the current
    location plus a zero offset (which is the same as the current location!).
    After it fails, it closes the pipe and reopens it (it does read some of the
    data before it tries to seek) which causes the writer to exit since the pipe
    was closed. Of course, now when it tries to read again it cannot open the
    file for reading because the writer has already closed it's end.

    You are right, there isn't much I can do....
    gthorpe, Jul 13, 2005
  4. gthorpe

    Hubble Guest

    Interestingly, the seeks would not move the file pointer anyway:
    Under some Unices and linux, you can "wrap" system calls if the
    programs use libc as shared library (nowadays the standard case). You
    can generate a shared library ( containing an lseek function,
    which ignores 0,SEEK_CUR and does the approriate lseek-syscall(2) - not
    lseek itself - call otherwise. This will (hopefully) not break the
    system. Your library can then be loaded by setting an environment
    variable (LD_PRELOAD under linux, solaris has a similar system). Iff
    you call ncsim <args>

    ncsim will happily use your own lseek. Don't ask me for details, I
    never did that. There are some thread libraries which do just that,
    redefining open,close,read,... system calls.

    Hubble, Jul 14, 2005
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