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A series of measurements of A# ./ubb-patgen -f 41kHz 1 A# ./ubb-patgen -f 41kHz -c B# ./ubb-la -f 12 -n 10 yielded these results: 1 3 gap 2 0 1 3 ------- ------- ------- ------- ------- ------- ------- 106 77 11 98 120 78 11 83 134 79 11 68 3 79 11 53 18 78 11 39 33 78 11 24 47 79 11 9 62 79 5 6 140 147 77 79 11 125 147 Where for example the last entry corresponds to ...1{146}3{77} 0{11}1{125}3{147}... Since this looks as if DAT1 was 1 for 77 samples before the first capture ended, was 0 throughout the pulling low of DAT0 (11 cycles), stayed low for another 125 cycles, and then went high for the 146.29 nominal half-period, we thus get a gap length of 2*146-77-11-125 = 79 |
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ubb-la.c |
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. 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