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95 lines
2.6 KiB
Plaintext
95 lines
2.6 KiB
Plaintext
UBB pattern capture
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===================
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ubb-la is the counterpart of ubb-patgen: it captures a pattern on DATx
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and prints on standard output what it has received. The output format
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is the same as the one used by ubb-patgen, i.e., hex digits with
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repetitions indicated by {number}.
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ubb-la is currently a proof of concept implementation and therefore
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only provides the most basic functions.
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Capture frequencies are the same as for ubb-patgen. The sample size is
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fixed at 8008 samples.
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Sample rate
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-----------
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The frequency in MHz is selected with the option -f. For example, this
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would select 10.5 MHz:
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# ubb-la -f 10.5
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bus 10.5 MHz controller 168 MHz
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Note that - unlike ubb-patgen - there are no SI prefixes or rounding
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modes to select. ubb-la simply picks the frequency closest to the one
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specified.
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The option -F works like -f but also allows frequencies that may
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exceed the hardware's capabilities. As a consequence, the MMC
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controller may hang.
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A list of available frequencies can be obtained with
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# ubb-patgen -q
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The default sample rate is 1 MHz.
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Clock output
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------------
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The CLK line (CLK/TRIG) is usually configured as an input. If the
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option -C is present, ubb-la outputs the MMC bus clock instead.
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Trigger
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-------
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Capture only starts after detection of a trigger. By default, ubb-la
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triggers when the CLK/TRIG line changes.
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The trigger pattern can be selected with the option -t pattern/mask,
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where ubb-la triggers when (pins & mask) == pattern
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For example,
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# ubb-la -t 2/3
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would monitor the lines DAT0 and DAT1 and trigger when DAT0 is 0
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while DAT1 is 1. In the pattern and mask, DAT0 has the value 1, DAT1
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is 2, DAT2 is 4, DAT3 is 8, and CLK/TRIG is 16.
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ubb-la turns off interrupts while waiting for a trigger. The only
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ways to exit are either detection of a trigger or a button press on
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the Ben's keyboard. In the latter case, ubb-la exits immediately and
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does not capture any samples.
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When the trigger is present, it takes roughly 550 +/- 250 ns plus one
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sample time until the first sample is taken.
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Known bugs
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----------
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At higher sample rates (observed at 42 and 56 MHz; not observed at
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24 MHz), the first sample may have an incorrect value and should be
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ignored.
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Interrupting ubb-la while a capture is in progress could cause
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memory corruption.
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The passive ubb-la circuit loads the inputs such that they will only
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work if there is a strong driver. In particular, signals held only by
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a pull-up or pull-down resistor are likely to be compromised.
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The respective resistive loads are:
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Signal To GND To 3.3 V
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(max) (max)
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------------------------
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DAT0 1.1 k 11 k
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DAT1-3 10 k 10 k
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TRIG 330 k 330 k
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