Jee Labs Talk

This forum has moved to forum.jeelabs.net - this read-only archive is for reference only!

1. tankslappa
   

   Please feel free to ignore the ramblings of a crazy man, but a thought has cross my mind...

   Right now I'm working on a project, and rapidly loosing my hair (although to be fair there wasn't much to start with)... What I could really do with is a 4 (or more) channel logic analyser... Now here comes the thought...

   Using direct port read on the ATmega328 I could read the state of the signals I am interested in fast enough, which is great. Unfortunately there is no way to get this information off the JeeNode fast enough (I can't read LED flashes that fast!). Serial over USB is just not going to cut it, and the ATmega is going to be far too busy for me to try to get it to do any kind of data compression.

   However, there is now this very interesting Ethercard available... Which supports a 100Mbit ethernet connection, so the question is, if I open a TCP (UDP?) connection between the Ethercard and a PC, how fast can a JeeNode and Ethercard (shouldn't that be JeeNet or JeeEth?) pump out a stream of bytes? As this is binary data I can combine two four channel samples into each byte, or one byte per sample for eight bit monitoring.

   I'm quite happy writing the PC TCP data processing side, that's easy.

   Posted 08/06/2010 10:52:44

2. jcw
   

   Current bottleneck seems to be the I/O with the ENC28J60, which is taking place with a 2 MHz SPI bit clock right now (since the RFM12B is limited to 2.5 MHz, and the master clock isn't adjusted constantly). A simple ping to the EtherCard takes 2 msec, for example. Also, for max throughput, you'll need to double-buffer the transmission, which isn't done in the current code.

   You could try to hack a JeeLink, which has 1 Mbyte data flash on board... that might give you 8 µsec per byte max throughput (SPI and flashing take time). Still a far cry from what simple logic analyzers can do. I use Zeroplus, which also does compression (and it has several protocol decoders, incl UART, I2C, SPI).

   Posted 08/06/2010 11:13:11

3. tankslappa
   

   Thanks for that JC, I suspected it wasn't going to be quite so easy (cheap!).

   I did think about buffering the data, and then sending it over the slow link but really wanted a constant data stream.

   Which Zeroplus do you have? I've looked at several models (on what must be some of the worst company websites I have seen in the UK). They appear to have various different buffers too, do they store locally and then send the data over "off-line" as it were too?

   Posted 08/06/2010 12:12:05

4. jcw
   

   Posted 08/06/2010 12:18:07

5. tankslappa
   

   Ah, I should have know you would have blogged it! ;-)

   Thanks JC...

   Is it too early to start writing to Santa?

   Posted 08/06/2010 12:25:19