Release of COAA PlanePlotter MLAT and SMU support for RPi
ppup1090 now supports Ground Stations functions required for MLAT and
SMU operation. This is *ONLY* available for RPi and similar linux
hardware.
Also included are sample startup scripts for dump1090 only and
dump1090+ppup1090 together.
view1090 was using close to 100% CPU before, with the non-blocking
commits and the reconnection code. sleep a bit between loop iterations
to keep CPU usage low.
CPU usage with this addition was down to <1% in testing.
A few minor additions and bug fixes as detailed below
1) Additional command line option "--net-buffer <n>" to specify the TCP
output buffer size. Default is n=0, which is 64Kb. Specify a value of n
to increase the buffer size according to Size = 64Kb * 2^n, so an n of
1 = 128Kb, n=2 is 256Kb etc. n is limited to 7, so the max size is 8Mb.
This option may assist if you have a high number of aircraft being
received, and an unreliable network connection, or if the receiving end
can be busy for an extended time.
2) Bug fix in ppup1090 which prevented the uploading of valid
ModeA/Squawk codes
3) Bug fix per Markus Grab's commit.
Variable j points to the current location in the magnitude vector.
When decoding a message (MODES_PREAMBLE_US+msglen)*2 is added to j.
In the loop head j is increased by 1, so one value was skipped.
Variable j points to the current location in the magnitude vector.
When decoding a message (MODES_PREAMBLE_US+msglen)*2 is added to j.
In the loop head j is increased by 1, so one value was skipped.
Make the modifications necessary to compile dump1090 for WinXP, Win7 and
hopefully Win8.
The files can be compiled using M$ Visual Studio/C++ 6.0. Due to various
licensing issues, I haven't included the libraries or DLLs. You will
need to locate pthreadVC2.lib and rtlsdr.lib to link the file, install
the zadig drivers to support the dongle, and locate libusb-1.0.dll,
msvcr100.dll, pthreadVC2.dll and rtlsdr.dll.
dump1090.exe will not run on any Windows version prior to XP SP2,
because msvcr100.dll imports several functions from the Windows kernel
that are not available on earlier versions. This means dump1090 won't
work on Win2K.
The major change to the code relates to file handles. The original code
assumes Linux behaviour in that handles are allocated from 0
sequentially upwards. However Windows handles are allocated pseudo
randomly, and handle numbers greater than 1024 would break the code. The
code has therefore been modified to use a linked list of connection
structures, rather than a static array limited to 1024 entries.
Some users have reported issues where the TCP link to dump1090 can be
lost at times of low traffic density - typically in the middle of the
night. One possible reason for this is that some routers drop the link
if there is no traffic for a predetermined period.
To try and resolve this, dump1090 now sends a 'null' packet consisting
of 7 "0x00" bytes approximately once a minute if there is no real
received traffic during this time. This packet should be discarded by
the application receiving the dump1090 because it will have an invalid
checksum, and ICAO address 0x000000 is also invalid. However, this null
packet should be enough to keep routers alive.
Thanks to Blort on the PP list.
The Beast binary message stream uses the 0x1a character a and escape to
mark the beginning of a new message. However, the 0x1a character could
occur in the body of a message since the message is binary. Therefore,
the 0x1a is repeated -as Blort put it :
This 56-bit Mode S Frame (containing a 1a) is supposed to look like
this:
1a 32 00 00 48 7b a6 1a 1a 0c 20 28 17 b0 c0 c3 b0
What is actually looks (looked) like (from wireshark) is this:
1a 32 00 00 48 7b a6 1a 0c 20 28 17 b0 c0 c3 b0
There are supposed to be two 1A’s (Gunter’s Escape Character) in a row
(1A 1A) whenever a data byte contains 1A, after the initial two 1A 3x
characters.
The Mutex on the RTL data reader thread does not "force" the data
processing thread to execute. Therefore, if the processor is busy, it is
possible for a second RTL callback to occur before the data from the
first has been processed. This will cause the loss of the first data,
but worse, it will cause a slip in the timestamp. This upsets Beamfinder
and MLAT operation in PlanePlotter.
To solve this, keep a Fifo buffer which is filled by the callback
thread, and emptied by the data processing thread. The fifo is the same
size as the number of buffers requested in the call to
rtlsdr_read_async().
Note - we only put the value of the pointer supplied in the callback
into the fifo. We do not attempt to cache the data in the buffer pointed
to by the pointer. This would require us to memcopy() 2Mbytes per
second, which we don't want to do if we don't have to because it will
only make the processor loading worse. Instead, we assume that the data
in the buffer will remain valid after the callback returns, at least
until it is overwritten by new data.
It is still possible for us to lose data if we can't process it quickly
enough. However, we can now detect this loss of data when the fifo is
almost full, and correct the timestamp for the lost block/blocks.
