mirror of
git://projects.qi-hardware.com/ben-blinkenlights.git
synced 2024-11-05 16:33:09 +02:00
116 lines
3.2 KiB
Plaintext
116 lines
3.2 KiB
Plaintext
UBB pattern capture
|
|
===================
|
|
|
|
ubb-la is the counterpart of ubb-patgen: it captures a pattern on DATx
|
|
and prints on standard output what it has received. The output format
|
|
is the same as the one used by ubb-patgen, i.e., hex digits with
|
|
repetitions indicated by {number}.
|
|
|
|
ubb-la is currently a proof of concept implementation and therefore
|
|
only provides the most basic functions.
|
|
|
|
Capture frequencies are the same as for ubb-patgen. The sample size is
|
|
fixed at 8008 samples.
|
|
|
|
|
|
Sample rate
|
|
-----------
|
|
|
|
The frequency in MHz is selected with the option -f. For example, this
|
|
would select 10.5 MHz:
|
|
|
|
# ubb-la -f 10.5
|
|
bus 10.5 MHz controller 168 MHz
|
|
|
|
Note that - unlike ubb-patgen - there are no SI prefixes or rounding
|
|
modes to select. ubb-la simply picks the frequency closest to the one
|
|
specified.
|
|
|
|
The option -F works like -f but also allows frequencies that may
|
|
exceed the hardware's capabilities. As a consequence, the MMC
|
|
controller may hang.
|
|
|
|
A list of available frequencies can be obtained with
|
|
|
|
# ubb-patgen -q
|
|
|
|
The default sample rate is 1 MHz.
|
|
|
|
|
|
Clock output
|
|
------------
|
|
|
|
The CLK line (CLK/TRIG) is usually configured as an input. If the
|
|
option -C is present, ubb-la outputs the MMC bus clock instead.
|
|
|
|
|
|
Trigger
|
|
-------
|
|
|
|
Capture only starts after detection of a trigger. By default, ubb-la
|
|
triggers when the CLK/TRIG line changes.
|
|
|
|
The trigger pattern can be selected with the option -t pattern/mask,
|
|
where ubb-la triggers when (pins & mask) == pattern
|
|
|
|
For example,
|
|
|
|
# ubb-la -t 2/3
|
|
|
|
would monitor the lines DAT0 and DAT1 and trigger when DAT0 is 0
|
|
while DAT1 is 1. In the pattern and mask, DAT0 has the value 1, DAT1
|
|
is 2, DAT2 is 4, DAT3 is 8, and CLK/TRIG is 16.
|
|
|
|
ubb-la turns off interrupts while waiting for a trigger. The only
|
|
ways to exit are either detection of a trigger or a button press on
|
|
the Ben's keyboard. In the latter case, ubb-la exits immediately and
|
|
does not capture any samples.
|
|
|
|
When the trigger is present, it takes roughly 550 +/- 250 ns plus one
|
|
sample time until the first sample is taken.
|
|
|
|
|
|
Graphical output
|
|
----------------
|
|
|
|
A graphical interface is available for exploration of a captured
|
|
pattern. This interface is invoked if the option -g is set. Note
|
|
that sample rate, trigger, etc., still have to be set up via the
|
|
command line. Example:
|
|
|
|
# ubb-la -f 12 -t 0/8 -g
|
|
|
|
In the GUI, the following keys are available:
|
|
|
|
Left/Right Pan the waveform left/right
|
|
Up/Down Zoom in/out
|
|
Space Set the user origin (upward-facing green triangle)
|
|
at the current position and display the time to
|
|
the center position (downward-facing blue triangle).
|
|
Pressing space again removes the user origin.
|
|
Enter/Q Quit
|
|
|
|
|
|
Known bugs
|
|
----------
|
|
|
|
At higher sample rates (observed at 42 and 56 MHz; not observed at
|
|
24 MHz), the first sample may have an incorrect value and should be
|
|
ignored.
|
|
|
|
Interrupting ubb-la while a capture is in progress could cause
|
|
memory corruption.
|
|
|
|
The passive ubb-la circuit loads the inputs such that they will only
|
|
work if there is a strong driver. In particular, signals held only by
|
|
a pull-up or pull-down resistor are likely to be compromised.
|
|
|
|
The respective resistive loads are:
|
|
|
|
Signal To GND To 3.3 V
|
|
(max) (max)
|
|
------------------------
|
|
DAT0 1.1 k 11 k
|
|
DAT1-3 10 k 10 k
|
|
TRIG 330 k 330 k
|