Speed oriented launch limiter is a nifty little feature that I always wanted to add to my ecus, but there was always a problem. The original rev/speed limit routines are written very closely to each other and are very hard to patch. In the ka24e ecu, the limiter works by looping at the routine a count of 3 times out of 4, instead of continuing, for each program cycle that the threshold (rpm or speed) is met.
Wanting to include a whole new algorithm with a new speed limit and a new rev limiter, I was in a pinch. So what is the solution? 16bits (or should I say 2 consectutive 8 bit chunks) of free ram
. This may be a bit hard to come by in some ecus depending on how much the code has been modified, but is required for this mod.So, instead of writing my launch routine near the original limiters, I simply use a routine elsewhere, in some free space, to choose which rev limiter to load from rom to to my free ram location, this is dictated by current speed. The original rev limiter routine is then changed so that it compares current RPM to the ram location rather than the original rom location.
I have this algorithm tested working on the bench, kind of like they do it on hondas.
something like this........
IF Speed < Launch_speed_set THEN
rev_limit = RAM (rom location 1)
IF Speed > Launch_speed_set THEN
rev_limit = RAM (rom location 2)
The only potential problem with this is that if a variable is not loaded into the ram location before the REV limiter routine, on the first program cycle, a rev limiter of zero will be experienced. This isnt really a big problem, either way, not exactly necessary.
Just something for those to ponder....