UBB pattern capture ("logic analyzer")

Werner Almesberger werner at almesberger.net
Fri Feb 1 02:39:16 EST 2013

I made a counterpart for the pattern generator: a capture solution
that uses the MMC controller and DMA to sample DATx.


- four digital channels

- capture rate 41 kSa/s to 56 MSa/s (142 different rates
  selectable), "overclocking" to 84 MSa/s can be attempted

- maximum continuous capture length about 8070 samples

- external trigger input. Trigger on any pattern on DATx and
  TRIG.  Delay to first sample is about 530 ns plus one sample

- GUI (running on the Ben) for exploration of the captured

The code lives here:

The usage is similar to ubb-patgen. It is described in

I made an extremely simple passive adapter that consists just
of UBB and two resistors:


It has an input impedance of 1.1 kOhm on DAT0 (11 kOhm during
capture) and 10 kOhm on DAT1-3, so it can only be used on signals
that are not easily disturbed. Adding buffers with better input
impedance is left as an exercise to the reader :-)

Schematics are here:

ubb-la can use the same cut-out labels as ubb-patgen.

The following picture shows ubb-la displaying a fake SPI pattern
generated by ubb-patgen running on the Ben sitting in the


- Werner

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