This avoids a confusing condition when hackrf_transfer is reading from
stdin with -R in which it does not repeat previous data but repeatedly
restarts reading new data after the user types Ctrl-D to indicate EOF.
The -R option should repeat previous data or should do nothing if the
input file cannot be rewound.
Fixes a bug introduced in 8a9af7a: Statistics skipped for initial
buffers not only when preloaded in TX mode but also in RX mode with no
preloading.
The total bytes transferred may appear inflated in RX mode when
receiving a small number of samples with -n, but the stats represent
data transferred over USB, some of which may have been discarded by the
host.
Instead of sending a signal to the process group, get our own process ID
and send the signal to it. This fixes a bug that prevented termination
when called from a script.
dBFS is defined in AES Standard AES17-1998, IEC 61606, and ITU-T Recs.
P.381 and P.382, such that the RMS value of a full-scale sine wave is
designated 0 dBFS.
A full scale sine wave on HackRF has the range -127 to 127.
We calculate the full scale ratio relative to a signal in which both I
and Q are held at 127. This represents a signal with sqrt(2) times
the amplitude, and thus twice the power, of a full scale sine wave.
Therefore to obtain dBfs by the above definition, we add 3dB.
The power measurement depends on the number of bytes that were valid
from the previous use of the transfer buffer.
The number of bytes to be read to fill the next transfer, is the full
size of the buffer.
The statistics reported to the user now reflect only completed USB
transfers and do not include information about the empty buffers that
are preloaded with data at the start of a TX operation.
Rather than using sleep() for 1s at a time, set up an interval timer
that will fire once per second, and wait in the main loop for either
this or some other event.
On POSIX, the timing is set up with setitimer(), which generates a
SIGALRM signal each time the timer fires. The main loop runs pause() to
wait for any signal.
On Windows, the timing is set up using CreateWaitableTimer, which
provides an event handle that is set each time the timer fires. The main
loop runs WaitForMultipleObjects() to wait on this and an interrupt
event.
The TX and RX callbacks can now stop the main loop immediately when they
stop streaming. This fixes#1019.
Using _MSC_VER here means that the choice of signal() versus
SetConsoleCtrlHandler depends on the compiler being used, rather
than the OS being targeted. When built with MinGW rather than MSVC,
this happens to work because MinGW's signal emulation is used, but
that emulation is quite limited.
Instead, be consistent and use the Win32 API when building for that
platform, regardless of compiler.
Note that if building for Cygwin, _WIN32 is not defined and POSIX
APIs are used.
