CDC run 1280 bad events
Below are the original sample values followed by the upsampled values for that same time, and then at 4 time-steps of 1.6ns later (calculated in C++, floating point arith). The first upsampled value should match the original value +/- 1. Clearly something is wrong here, first with the original data (contains discontinuities) and then with the upsampled data.
sample: 45 original: 57 upsampled: 57 54 50 48 46 sample: 46 original: 44 upsampled: 45 44 45 46 49 sample: 47 original: 51 upsampled: 51 55 59 63 67 sample: 48 original: 71 upsampled: 72 76 81 86 92 sample: 49 original: 94 upsampled: 98 103 107 110 110 sample: 50 original: 117 upsampled: 108 107 113 130 162 sample: 51 original: 174 upsampled: 207 260 311 346 353 sample: 52 original: 375 upsampled: 331 287 241 220 245 sample: 53 original: 257 upsampled: 334 485 680 889 1075 sample: 54 original: 1287 upsampled: 1212 1289 1316 1316 1323 sample: 55 original: 1294 upsampled: 1365 1458 1602 1780 1962 sample: 56 original: 2196 upsampled: 2126 2254 2342 2399 2436 sample: 57 original: 2423 upsampled: 2469 2502 2534 2552 2542
Used C++ version of the integer arithmetic that is used in the VHDL code
C++ leading edge algo output: Searching for ADC value >= 300, ADC values surrounding the threshold crossing are ADC[41] 108 ADC[42] 98 ADC[43] 89 ADC[44] 77 ADC[45] 57 ADC[46] 44 ADC[47] 51 ADC[48] 71 ADC[49] 94 ADC[50] 117 ADC[51] 174 ADC[52] 375 Subset of ADC values sent to the upsampling routine: adc_subset[0] 89 adc_subset[1] 77 adc_subset[2] 57 ... adc_subset[9] 375 adc_subset[10] 257 adc_subset[11] 1287 ... up to adc_subset[14] 2423 thresholds: hi 231 lo 111 threshold 231 met or exceeded by sample 9 value 375 adc[8] 174 adc[7] 117 adc[6] 94 threshold 111 met or preceded by sample 6 value 94 itime1 60 x 0.1 samplesThe low timing threshold is now known to be between samples 6 and 7, so upsampled points are calculated from 5.8 to 7.2. These are searched from the last point back to the first, looking for a value which matches or is lower than the low timing threshold (111).
Upsampled values 1 (97) and 6 (107) should match the raw values for samples 6 (94) and 7 (117), respectively. They do not. The next stage in the calculation is to interpolate between the two points surrounding the threshold crossing but in this case the first point (upsampled 7) was less than the threshold, it all goes horribly wrong.upsampled 0 91 upsampled 1 97 upsampled 2 102 upsampled 3 107 upsampled 4 110 upsampled 5 109 upsampled 6 107 upsampled 7 107
threshold 111 met or preceded by upsampled point 7 value 107 itime2 14 x 0.1 samples
denom -107 limit 8
VHDL simulation output: at 308 ns(1): Note: upsampled: iubuf(0) 91 (/findtime_tb/uut/). at 460 ns(1): Note: upsampled: iubuf(1) 97 (/findtime_tb/uut/). at 612 ns(1): Note: upsampled: iubuf(2) 102 (/findtime_tb/uut/). at 748 ns(1): Note: upsampled: iubuf(3) 107 (/findtime_tb/uut/). at 884 ns(1): Note: upsampled: iubuf(4) 110 (/findtime_tb/uut/). at 1036 ns(1): Note: upsampled: iubuf(5) 109 (/findtime_tb/uut/). at 1188 ns(1): Note: upsampled: iubuf(6) 107 (/findtime_tb/uut/). at 1340 ns(1): Note: upsampled: iubuf(7) 107 (/findtime_tb/uut/). at 1348 ns(1): Note: i 7 adc val 107 lo thres 111 (/findtime_tb/uut/). at 1348 ns(1): Note: adc_sample_lo2 7 (/findtime_tb/uut/). at 1348 ns(1): Note: itime2 14 x 0.1samples (/findtime_tb/uut/). at 1356 ns(1): Note: denom -107 (/findtime_tb/uut/). at 1356 ns(1): Note: limit 8 (/findtime_tb/uut/). at 1364 ns(1): Note: sum -107 ifrac 1 (/findtime_tb/uut/). at 1372 ns(1): Note: sum -214 ifrac 2 (/findtime_tb/uut/). at 1380 ns(1): Note: sum -321 ifrac 3 (/findtime_tb/uut/). at 1388 ns(1): Note: sum -428 ifrac 4 (/findtime_tb/uut/).
The good news is that the VHDL and C++ codes give the same results before VHDL descends into a spiral of doom.
The fix for the bug would be to test if upsampled[7] is <= the low timing threshold, if so then bail out with a rough time and an error code.
sample: 35 original: 115 upsampled: 116 116 116 118 121 sample: 36 original: 122 upsampled: 126 131 136 141 145 sample: 37 original: 157 upsampled: 149 154 165 184 214 sample: 38 original: 239 upsampled: 255 302 349 388 410 sample: 39 original: 420 upsampled: 410 386 343 290 237 sample: 40 original: 189 upsampled: 198 183 201 255 345 sample: 41 original: 456 upsampled: 464 602 746 882 996 sample: 42 original: 1109 upsampled: 1080 1131 1154 1157 1151
threshold 275 met or exceeded by sample 9 value 420 adc[8] 239 adc[7] 157 adc[6] 122 threshold 155 met or preceded by sample 6 value 122 itime1 60 x 0.1 samples upsampled 0 121 upsampled 1 125 upsampled 2 130 upsampled 3 136 upsampled 4 141 upsampled 5 145 upsampled 6 148 upsampled 7 154 threshold 155 met or preceded by upsampled point 7 value 154
Same problem as previous, same fix.
Here is a normal event (8 out of 2.3 million CDC hits in the first part of this run had the problem shown above)
sample: 35 original: 80 upsampled: 80 79 78 76 75 sample: 36 original: 73 upsampled: 73 72 70 68 67 sample: 37 original: 65 upsampled: 65 64 63 62 62 sample: 38 original: 62 upsampled: 62 64 66 68 72 sample: 39 original: 75 upsampled: 75 79 83 86 89 sample: 40 original: 91 upsampled: 91 92 93 93 92 sample: 41 original: 92 upsampled: 92 92 92 92 92 sample: 42 original: 93 upsampled: 93 94 94 95 95 sample: 43 original: 96 upsampled: 96 96 96 96 95 sample: 44 original: 95 upsampled: 95 95 94 94 94 sample: 45 original: 93 upsampled: 93 92 91 89 87 sample: 46 original: 85 upsampled: 85 83 81 78 77 sample: 47 original: 75 upsampled: 75 75 75 75 77 sample: 48 original: 79 upsampled: 79 82 85 89 94 sample: 49 original: 98 upsampled: 98 102 106 109 111 sample: 50 original: 113 upsampled: 113 113 112 110 107 sample: 51 original: 103 upsampled: 103 98 92 86 81 sample: 52 original: 75 upsampled: 75 71 67 65 64 sample: 53 original: 64 upsampled: 64 66 69 74 79 sample: 54 original: 84 upsampled: 85 91 96 102 106 sample: 55 original: 108 upsampled: 110 113 115 116 117 sample: 56 original: 115 upsampled: 118 121 125 134 146 sample: 57 original: 159 upsampled: 164 187 218 257 302 sample: 58 original: 351 upsampled: 354 413 477 547 619 sample: 59 original: 693 upsampled: 693 767 840 911 978 sample: 60 original: 1044 upsampled: 1040 1095 1144 1185 1218 sample: 61 original: 1250 upsampled: 1243 1259 1268 1269 1262 sample: 62 original: 1255 upsampled: 1248 1229 1204 1175 1142 sample: 63 original: 1110 upsampled: 1106 1068 1029 988 948 sample: 64 original: 908 upsampled: 907 867 827 788 750 sample: 65 original: 712 upsampled: 713 678 645 613 583 sample: 66 original: 554 upsampled: 556 531 509 489 471 sample: 67 original: 454 upsampled: 456 443 432 423 415 sample: 68 original: 408 upsampled: 409 405 401 397 394 sample: 69 original: 390 upsampled: 390 386 382 376 370 sample: 70 original: 363 upsampled: 363 355 347 338 329 sample: 71 original: 320 upsampled: 320 310 301 291 281
This is spot on until the adc value rises sharply, from then on there are small discrepancies (0 to 5) and larger ones (6 to 8) when above 1000. We are most interested in the region just above pedestal (ie 100-150).
Entry 83 eventnum 4 channelnum 3 rocid 25 slot 8 channel 49 nsamples 180 Searching for ADC value >= 288 ADC[36] 73 ... ADC[57] 159 ADC[58] 351 adc_subset[0] 98 adc_subset[1] 113 adc_subset[2] 103 adc_subset[3] 75 adc_subset[4] 64 adc_subset[5] 84 adc_subset[6] 108 adc_subset[7] 115 adc_subset[8] 159 adc_subset[9] 351 adc_subset[10] 693 adc_subset[11] 1044 adc_subset[12] 1250 adc_subset[13] 1255 adc_subset[14] 1110 thresholds: hi 244 lo 124 threshold 244 met or exceeded by sample 9 value 351 adc[8] 159 adc[7] 115 threshold 124 met or preceded by sample 7 value 115 itime1 70 x 0.1 samples upsampled 0 116 upsampled 1 118 upsampled 2 120 upsampled 3 125 upsampled 4 133 upsampled 5 145 upsampled 6 163 upsampled 7 187 threshold 124 met or preceded by upsampled point 2 value 120
Upsampling error check
After excluding known CDC_bad_channels I compared the upsampled data with the original samples for the first 10000 events of run 1602. This is a high-intensity run so some of the pedestals are lower than they should be.
ups_err1 is the upsampled value iubuf[1] - the original sample adc[adc_sample_lo]
ups_err2 is the upsampled value iubuf[6] - the original sample adc[adc_sample_lo+1]
q_code list: 0: Good 1: ADC data did not go over threshold adc_thres_hi 2: Leading edge time is outside the upsampled region (cross adc_thres_lo too late in the buffer subset ) 3: Last upsampled point is <= low timing threshold 4: Upsampled points did not go below low timing threshold
Extremely steep gradients are likely to cause a problem so check what happens when the adc saturates:
Improved code
Upsampled value can be negative following a dip between two small sampled values, catch this & bail out from algorithm. q_code=8 when any upsampled value<0
Total entries in file is 1366697
Entries are removed from processing as q_code>0 in this order...
| q_code | reason | entries | percent of total entries |
|---|---|---|---|
| 5 | ADC value = 0 | 53828 | 4% |
| 6 | ADC value = 4095 | 99891 | 7% |
| 7 | Ped > 511 | 47052 | 3% |
| 1 | ADC data did not go over threshold adc_thres_hi | 10179 | 1% |
| 2 | Leading edge time is too late in the buffer (outside the upsampled region) | 820 | 0.06% |
| 8 | Upsampled value is negative | 396 | 0.03% |
| 3 | Last upsampled point is too low (below or equal to low timing threshold) | 5 | 0.0004% |
| 4 | Upsampled points are too high (did not go below low timing threshold) | 7903 | 0.6% |
| 0 | Good | 1146623 | 84% |
Looking at upsampling errors - occur when gradient is very large
