On 09/24/2013 03:30 PM, Paul Fertser wrote: >> If you have signal integrity issues, increasing the drive strength of the >> outputs may actually make the problem worse due to increased ringing. > So true. Do you probably have any suggestions on how to use > raspberrypi without additional buffers? What series resistors > should be attached and what would be the best drive strength in this > case?
I would guess maximum drive strength combined with the right series resistors - you will have to attach a scope to determine these, as the proper matching depends on the output impedance of the RPi's drivers, and the cable impedance. Using a flat cable with every second pin grounded will help to reduce crosstalk and get a constant impedance. A ribbon cable with every second pin grounded should have around 100 Ohm impedance, so 80-100 Ohm resistors should provide a good starting point. Observe proper high-speed probing techniques when attaching the scope - you will probably need 60MHz or more bandwidth, and a *short* gound lead on the probe (best none at all) to get useful results. Measure close to the target - a source-terminated signal will show reflections everywhere except at the end of the line. (see http://www.signalintegrity.com/Pubs/straight/probes.htm if you don't know already). cu Michael ------------------------------------------------------------------------------ October Webinars: Code for Performance Free Intel webinars can help you accelerate application performance. Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from the latest Intel processors and coprocessors. See abstracts and register > http://pubads.g.doubleclick.net/gampad/clk?id=60133471&iu=/4140/ostg.clktrk _______________________________________________ OpenOCD-devel mailing list OpenOCD-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/openocd-devel
