tonyb wrote: > I would guess that the interesting pieces of a data trace do not > compress well. I think that the parallel port can give us 1Mb/s. > Perhaps this would be a better choice than the serial port. > > Tony > > Timothy Miller wrote: >> On 1/2/07, tonyb <[EMAIL PROTECTED]> wrote: >>> "Standard" lossless compression will reduce the amount of data by less >>> than a factor of four. It would still take over an hour to move the >>> data over the serial line. >> >> That all depends on the nature of the data. How compressible is a >> file filled with nothing but NUL characters? >> >> There are two methods for doing compressed captures that I can think of right off hand. Both are value change formats but each would yield smaller results in different situations.
First is to do bit wise capture. At the start of the capture, save the value of all the bits to be watched. From that point, each time a bit flips, save the time offset. The other option is to do a "bus capture" each time an bits on the bus change. You need to save all the bits you are watching plus the time stamp. Either way, we won't be able to determine floating values. The PCI bus isn't supposed to be allowed to float so it shouldn't be a huge deal, but a really mis-behaving card that tried to drive the bus at the same time as another card may not be readily detectable. Neither of the above methods really compress the datastream from the card to the display system, they just let us transfer more information with less bytes. If we can do all the capture in the XP10, the Spartan-3 would give us plenty of real estate to put a moderately powerful cpu core. If we use any type of value change or "pre-compressed" format, I don't think RLE compression will buy us much of anything since the data would effectively already be RLE compressed at capture time. Perhaps some sort of Huffman encoding. We could generate the encoding table on the fly at capture time and have the CPU core compress on the fly using the encoding table at transmission time. Another option might be to make a daughter board with the appropriate drivers and termination for a simple SCSI bus. Even a simple SCSI-1 bus would allow for a full download in less than a minute, uncompressed. Patrick M _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
