Currently we use a fixed Integrator Time Constant, but after thinking about this and discussing it with MembersPage/DavidBlades it has become apparent that the time constant actually needs to decrease as engine speed increases. The reason for this is that the knock window time decreases with engine speed, so we need to increase the resolution to view the events in that time period more closely.
David calculated the time constant and worked out that at 500rpm the Time constant would need to be ~600uSec which is the highest time constant available with the TPIC8101, at ~8250rpm the Time constant would need to be ~40uSec (the lowest available constant with the TPIC)
[Additional from dnb] The time constants I calculated are merely to make the best use of the range available in the chip. The "best fit" I could come up with has approximately 30 time constants per window. This is not certain to be optimal, but it is consistant across RPM. I suggest that a parameter be entered in the config called something like "timeconstants_per_window" In my case this is 30, but it is equally valid to use 15 or 20.
Using the data from the calculations with the fixed time constants the following RPM to Time Constants(TC)
| TC Prog. Value | TC uSec | RPM |
| 31 | 600 | 555 |
| 30 | 560 | 595 |
| 29 | 520 | 640 |
| 28 | 480 | 694 |
| 27 | 440 | 757 |
| 26 | 400 | 833 |
| 25 | 360 | 926 |
| 24 | 320 | 1042 |
| 23 | 300 | 1111 |
| 22 | 280 | 1190 |
| 21 | 260 | 1282 |
| 20 | 240 | 1388 |
| 19 | 220 | 1515 |
| 18 | 200 | 1666 |
| 17 | 180 | 1851 |
| 16 | 160 | 2083 |
| 15 | 150 | 2222 |
| 14 | 140 | 2380 |
| 13 | 130 | 2564 |
| 12 | 120 | 2777 |
| 11 | 110 | 3030 |
| 10 | 100 | 3333 |
| 9 | 90 | 3703 |
| 8 | 80 | 4166 |
| 7 | 75 | 4444 |
| 6 | 70 | 4761 |
| 5 | 65 | 5128 |
| 4 | 60 | 5555 |
| 3 | 55 | 6060 |
| 2 | 50 | 6666 |
| 1 | 45 | 7407 |
| 0 | 40 | 8135 |
When the TC uSec values are plotted you'll see that there are changes in the gradient this occurs every 8 cells at the RPM values of 1111, 2222, 4444 (I dont know if this is significant).
There seems little point in looking for detonation at points 25 to 31 (926rpm to 555rpm) so we need only deal with 24 values to map the RPM to the time constant.
The question is... how best to code this?