are featuring USB interfaces realised with integrated circuits that can lead
to system cra-
shes when used with a FM-SPY. Such situations are seldom but if they occur they can lead to very bad
system performance, system crashes ect. It's important to know that such behaviour is not a bug - and
therefore cannot be fixed - but merely a difficult constellation of unlucky circumstances.
The FM-SPY hardware box isn't featuring a lot of processing power for it sends all raw data to the PC
for number crunching. This principle is the main reason for the low cost of the FM-SPY. On the other
hand this leads to a fast datastream from the FM-SPY to the computer through the USB interface. In
order to be able to connect not only brand new computers MEDIA ENGINEERING has chosen to use
the USB version 1.1 interface. This one interface is also used in case a newer computer with USB2.0
is connected for the operating system steps down the USB interface automatically from version 2.0 to
1.1. The FM-SPY is converting the full bandwidth MPX signal as well as the antenna signal strength sig-
nal into 16bit words 400'000 times a second. This leads - together with some margin for security and
protocol and overhead - approximately 7Mbps. This speed is more than half of the maximum perfor-
mance of USB1.1 of 12Mbps. Such a huge amount of data can be transferred from the FM-SPY to the
PC only in a so called iso-streaming mode. This mode is different from the normally and most often
used bulk-mode in not using any back and forth control mechanisms and checks. It's very similar to a
pure streaming rsp. broadcasting where the receiver cannot stop the sender from sending out more
data in case the transmission quality has gone bad.
If, e.g., an USB mouse (a typical USB bulk-mode device) is connected to the same PC as the FM-SPY,
the data transfer mode has to be stopped and switched in a rapid sequence. Not only it's possible that
some of the data of the FM-SPY data stream is lost but the fast and rapid mode-switching can lead to
problems with the USB interface circuitry as well as its firmware in the PC. Many unexpected results in-
cluding complete system crashes can occur for this problem is occurring on a very low hardware re-
WORK AROUND: (if the above mentioned problems occur) never connect the FM-SPY plus other USB
devices to the PC at the same time.
Please bear in mind that even some mouse-pads built-into notebooks might act as USB mice!