Re: Openeeg-list Digest, Vol 78, Issue 4

OpenEEG's firmware should show it pretty plainly...

Here's some grabbed from the headers of the source files

////////// Packet Format Version 2 ////////////

// 17-byte packets are transmitted from the ModularEEG at 256Hz,
// using 1 start bit, 8 data bits, 1 stop bit, no parity, 57600 bits per
second.

// Minimial transmission speed is 256Hz * sizeof(modeeg_packet) * 10 =
43520 bps.

struct modeeg_packet
{
uint8_t sync0; // = 0xa5
uint8_t sync1; // = 0x5a
uint8_t version; // = 2
uint8_t count; // packet counter. Increases by 1 each packet.
uint16_t data[6]; // 10-bit sample (= 0 - 1023) in big endian (Motorola)
format.
uint8_t switches; // State of PD5 to PD2, in bits 3 to 0.
};

//////////////////////////////////////////////////////////////

/*
 * ModularEEG Packet Format Version 3
 *
 * One packet can have zero, two, four or six channels (or more).
 * The default is a 6-channel packet, shown below.
 *
 * 0ppppppx     packet header
 * 0xxxxxxx
 *
 * 0aaaaaaa     channel 0 LSB
 * 0bbbbbbb     channel 1 LSB
 * 0aaa-bbb     channel 0 and 1 MSB
 *
 * 0ccccccc     channel 2 LSB
 * 0ddddddd     channel 3 LSB
 * 0ccc-ddd     channel 2 and 3 MSB
 *
 * 0eeeeeee     channel 4 LSB
 * 0fffffff     channel 5 LSB
 * 1eee-fff     channel 4 and 5 MSB
 *
 * Key:
 *
 * 1 and 0 = sync bits.
 *   Note that the '1' sync bit is in the last byte of the packet,
 *   regardless of how many channels are in the packet.
 * p = 6-bit packet counter
 * x = auxillary channel byte
 * a - f = 10-bit samples from ADC channels 0 - 5
 * - = unused, must be zero
 *
 * There are 8 auxillary channels that are transmitted in sequence.
 * The 3 least significant bits of the packet counter determine what
 * channel is transmitted in the current packet.
 *
 * Aux Channel Allocations:
 *
 * 0: Zero-terminated ID-string (ASCII encoded).
 * 1:
 * 2:
 * 3:
 * 4: Port D status bits
 * 5:
 * 6:
 * 7:
 *
 * The ID-string is currently "mEEGv1.0".
 */

//////////////////////////////////////////////////////////////

And here's the packet entry from the bidirectional source.

\subsection Packet Format Version 3 (bidirectional, number of channels
selectable, evoked potentials supported)

 If you select all 6 channels and the backchannel isn't used, this is
compatible to the Electric Guru/BWview protocol.
 So this is the default configuration. Only if you send commands to change
the protcol it won't be compatible anymore.
 The number of channels can be reduced for a reduced data rate.
 9 to 17 byte packets are transmitted from the ModularEEG at approx. 256Hz,
 using 1 start bit, 8 data bits, 1 stop bit, no parity, 57600 or 115200
bits per second.  \n \n


struct modeeg_packet3 \n
{                       \n
uint8_t sync0;  // = 0xa5\n
uint8_t sync1;  // = 0x5a \n
  uint8_t   sidechannel;// channel can be used to send messages from EEG to
PC (sends a 2 if not used, for compatibility \n
uint8_t count;  // packet counter. Increases by 1 each packet \n
uint16_t 2-6;      // 10-bit sample (= 0 - 1023) in big endian (Motorola)
format, channel order 1,4,2,5,3,6 \n
uint8_t switches;  // State of PD5 to PD2, in bits 3 to 0, and state of EVP
Stimulus in bits 7 to 4 \n
}; \n \n

 \warning Channel order is 1,4,2,5,3,6 for minimum skew between channels on
one amplifier board (the first amplifier
 board has channels 1 and 4, the second 2 and 5, the third 3 and 6).  \n \n

 Note that data is transmitted in big-endian format.
 By this measure together with the unique pattern in sync0 and sync1 it is
guaranteed,
 that re-sync (i.e after disconnecting the data line) is always safe. The
number of
 channels can be selected (2,4 or 6).


On Fri, Nov 16, 2012 at 4:34 PM, Gregory Perry
<[email protected]>wrote:

>  Thanks Paddy. What's the speed of that COM port, any ideas? Hopefully
> 115K...
>
>  *From*: Paddy Duncan [mailto:[email protected]]
> *Sent*: Friday, November 16, 2012 02:52 PM
> *To*: 'Discussion of EEG hardware, software, training protocols, NFB
> theory - for developers and users.' <[email protected]>
> *Subject*: Re: [Openeeg-list] Openeeg-list Digest, Vol 78, Issue 4
>
>
> I've tried searching for such a document myself without much luck but...**
> **
>
> ** **
>
> For the OpenEEG it is 17 byte packets as follows:****
>
> ** **
>
> First two bytes 0xA5 and 0x5A (sync bytes)****
>
> Third byte 0x02 (version of the firmware)****
>
> Fourth is packet counter incrementing by 1 each packet****
>
> Then 6 pairs of bytes (2 bytes for each of 6 channel in 10-bit resolution)
> ****
>
> 17th byte is 0x0f****
>
> ** **
>
> I would assume that this would be the same for the USB-EEG, as BrainBay
> etc are recommended as software.****
>
> It appears that the USB-EEG uses a virtual COM port in order to be
> compatible with the software (just as I now use a Serial-USB converter +
> Virtual com port).****
>
> ** **
>
> Hope this helps.****
>
> ** **
>
> Paddy****
>
> ** **
>
> ** **
>
> ** **
>
> *From:* Gregory Perry [mailto:[email protected]]
> *Sent:* 16 November 2012 19:13
> *To:* Discussion of EEG hardware, software, training protocols, NFB
> theory - for developers and users.
> *Subject:* Re: [Openeeg-list] Openeeg-list Digest, Vol 78, Issue 4****
>
> ** **
>
> Is there a document that describes the raw data output from an openEEG
> device such as the EEG-SMT (framing etc)?  How is that information
> presented to the host computer via USB?  Is it just a serial interface on
> the PC side? ****
>
> ** **
>   ------------------------------
>
> *From:* Stefan Jung [[email protected]]
> *Sent:* Tuesday, November 13, 2012 12:09 AM
> *To:* [email protected]
> *Subject:* Re: [Openeeg-list] Openeeg-list Digest, Vol 78, Issue 4****
>
> Mike****
>
>  ****
>
> An EEG amplifier's sole purpose is to sample data and send this (raw) data
> to the PC host.  If your PC app can connect and sync on that data, the work
> is done.****
>
>  ****
>
> "Functions" are the reserve of the software app.****
>
>  ****
>
> It would also help to be more specific as to which functions you are
> talking about.****
>
>  ****
>
> Stefan****
>
>
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