View source for Technical Reference:BCI2000 Messages

====Descriptor Supplement=1: Signal Data====
For brain signals, the ''descriptor supplement'' is 1. 
The ''data type'' can be   
*0 <tt>(SignalType::int16)</tt> for integers in little endian format. 
*1 <tt>(SignalType::float24)</tt> for 3-byte floating-point values in a BCI2000-specific encoding. There, the first two bytes define the mantissa <math>A</math> as a signed two-byte integer in little endian format, and the third byte defines the exponent <math>B</math> as a signed one-byte integer. The actual floating point value is then calculated as <math>A*10^{B}</math>. 
*2 <tt>(SignalType::float32)</tt> for 4-byte floating-point values in IEEE 754 format, transmitted in little endian byte order. 
*3 <tt>(SignalType::int32)</tt> for 4-byte signed integer values, transmitted in little endian byte order. 

The number of channels and samples are sent as "length fields" in the sense explained above, using binary encoding for small numbers, and ASCII representation to allow for arbitrarily large numbers.

Note that the ''Source identifier'' field may be set to <tt>0xff</tt> and is then followed with a null-terminated string representing a string-valued source identifier.

[[Image:BCI2000_Messages_vistype1(graph).png|center|thumb|600px|One message if the visualization type is 1 (signal data).]]

[[Image:BCI2000_Messages_TransmittedVisualizationDataFormat.png|center|thumb|500px|Graphical representation of the transmitted visualization data format.]]

If data transmission is done locally (i.e, between modules on the same machine), the ''data type'' can have its 6th bit set (add 64 to the values above). In this case, only a reference to a region of shared memory is transmitted in the message; the actual data is located in the shared memory region as a sample-first matrix in 8-byte IEEE 754 ''double'' format, in the machine's native byte order. Note that the lower bits of the data type still carry information about the actual resolution of the data, even if the representation is ''double''. If the ''shared'' bit is set in the ''data type'' field, it is followed with the number of channels and samples as normal, but then followed with a null-terminated string which is the name or path of a shared memory object, allowing the receiving end to connect to that object and read the actual data.