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mirror of git://projects.qi-hardware.com/ben-blinkenlights.git synced 2024-11-04 23:08:07 +02:00
ben-blinkenlights/ubb-la
Werner Almesberger bf62b209e5 ubb-la/ubb-la.c: raise MMC bus clock to 84 MHz during overhead
We also de-optimize the start bit (DAT0=0) phase for now. In the
12 MHz scenario, this produces the following results:

1       3       gap+0   2       0       1       3
------- ------- ------- ------- ------- ------- -------
8               38              26      100     146
        102     38      26                      6
        52      39      26                      55
        147     41      26                      105
97              39              26      10      146

Note that the gap now includes the start bit phase, since the clock
change may complicate the calculation of how many 12 MHz samples
it corresponds to.
2013-01-28 23:24:29 -03:00
..
hw ubb-la/hw/: proof-of-concept passive LA adapter board 2013-01-23 11:52:11 -03:00
Makefile ubb-la/Makefile (CFLAGS): use more specific -O9 -fno-tree-cselim 2013-01-25 19:49:20 -03:00
README ubb-la/ubb-la.c: new option -F freq_MHz to select "unsafe" frequencies 2013-01-28 21:06:00 -03:00
ubb-la.c ubb-la/ubb-la.c: raise MMC bus clock to 84 MHz during overhead 2013-01-28 23:24:29 -03:00

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.


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