The prior code uses questionable casts to do what can be done with
modulo integer math.

The new code does not give *exactly* the same timeout, because the
calculation
    (int)(float)(this_mb_tx->mb_response_timeout_ms / 1000.0)
is subject to rounding errors, while
    timeout.tv_sec  = this_mb_tx->mb_response_timeout_ms / 1000;
is not.  For example for a response timeout of 2001ms, the old code
would actually give a timeout of 2.000999 seconds, while the new code
gives the correct result of 2.001000 seconds.  The new code begins
giving "radically" different (but again more correct) values around
65536 seconds due to the loss of precision in float arithmetic
(65536.000f == 65536.001f when you have a 24-bit mantissa)

Tested by cut&paste of old and new code into a test harness:

struct timeval fold(long arg)
{
    struct timeval timeout;
    timeout.tv_sec  = (int)(float)(arg / 1000.0);  //int part of the float
    timeout.tv_usec = ((float)(arg / 1000.0) - timeout.tv_sec) * 1000000;
    return timeout;
}

struct timeval fnew(long arg)
{
    struct timeval timeout;
    timeout.tv_sec  = arg / 1000;
    timeout.tv_usec = (arg % 1000) * 1000;
    return timeout;
}

void check(long timeout) {
    struct timeval ta = fold(timeout);
    struct timeval tb = fnew(timeout);

    double a = ta.tv_sec + ta.tv_usec * 1e-6;
    double b = tb.tv_sec + tb.tv_usec * 1e-6;
    if(fabs(a - b) > .001) {
    // if(ta.tv_sec != tb.tv_sec || ta.tv_usec != tb.tv_usec) {
        printf("fail tv_sec %lu: %lu.%06lu != %lu.%06lu\n", timeout,
            (long) ta.tv_sec, (long) ta.tv_usec,
            (long) tb.tv_sec, (long) tb.tv_usec);
    }
}

int main() {
    long i;
    for(i=0; i<1000*1000*1000; i += 500) {
        check(i);
        check(i+1);
        check(i+499);
    }
}

By default, configure will now look for libmodbus (installed from a
separate deb, provided by Ubuntu for Precise and by the linuxcnc.org
debian archive for Hardy and Lucid) and error out if it can't be found.

The user can disable this check (and disable compilation of all drivers
that use libmodbus) by configuring with "--without-libmodbus".

- Arduino example added.
  Tested with Arduino Mega 2560 R3 using Modbusino over USB at 115200 bps.
- New parameters in config file.
  HAL_MODULE_NAME, MB_RESPONSE_TIMEOUT_MS and MB_BYTE_TIMEOUT_MS.
- New HAL pin "num_errors" for each transaction. num_errors = 0 if last
  transaction OK, else the count of failed transactions.
- Fix a bug, OPTIONAL's parameters may be 0 instead of default value if
  not specified in 1st transaction.

Signed-off-by: Michael Haberler <git@mah.priv.at>

- Mb2hal now uses libmodbus3 instead of the old libmodbus file
  located in src/hal/user_comps/modbus.c used by gs2_vfd.c
  # Also fix a TIMEOUT bug (due to this unpatched old libmodbus file).
- Better INI file documentation (HOW-TO).
- Better Submakefile.
- Source code cleaned and reordered.
  # Now is posible to add new functionallity.

See LogBook.txt for more information.

Signed-off-by: Michael Haberler <git@mah.priv.at>

Nothing big, two instances of dead initialization (so, a variable is
explicitly set at define-time, but then written to again before being read).

Signed-off-by: Sebastian Kuzminsky <seb@highlab.com>

This reverts commit ca835b429478324639df779e26005ca43b8917d1.

Victor says it is needed.

Userspace HAL component to communicate with one or
more Modbus devices.

Tests:
- TCP some functions = Remote IO Delta RTU-EN01,
  24 inputs, 8 outputs.
- RS232 some functions = Servo Drive Delta ASDA-B (1021-A 1Kw).
- TCP all functions = MoD_RsSim V8.20 (www.plcsimulator.org)
  on Windows XP SP3.

Signed-off-by: Michael Haberler <git@mah.priv.at>