On Tue, Sep 24, 2013 at 01:52:10PM +0200, Michael Schwingen wrote: > On Tue, Sep 24, 2013 at 02:49:17PM +0400, Paul Fertser wrote: > > I've seen blackmagicprobe failing to connect until I attached another > > ground line. And someone on IRC reported he used 3 ground lines until > > it started to work. > > Sounds reasonable - JTAG can be quite fast (in terms of rise/falltime, not > clock speed), so you may run into signal integrity issues. Having one > ground wire per fast signal is good practice, and a series resistor at the > source that roughly matches the cable impedance may also help (unless you > are using very short cables, ~5cm or less).
You're right indeed. I have completely forgotten about that, even though I know proper JTAG adapters have integrated series termination to suppress ringing. > 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? -- Be free, use free (http://www.gnu.org/philosophy/free-sw.html) software! mailto:fercer...@gmail.com ------------------------------------------------------------------------------ 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
