create_j1939db-json.py: wrong spn_startbit_inpgn for positions mixing - and ,

[BenGardiner]

CC: @j4l-Shvn

e.g. SPN 8839 which lists position 3-4, 5.6 (in 201910 DA)

this is decoded as [16, 357] from

pretty_j1939/create_j1939db-json.py

Line 172 in 3d5f7f7

def get_spn_start_bit(contents):

@j4l-Shvn: I think your read of 1939-71 is correct https://github.com/j4l-Shvn/pretty_j1939/blob/3700b0abf51500c8a43a43b19be65313914e2787/create_j1939db-json.py#L174 BUT it seems like the authors of the DA do not treat the - and , the same.

I think 3-4, 5.6 should be interpreted as 8 bits at byte 3, 8 bits at byte 4 and remaining bits at "position" 5.6 (byte 5, 6th bit)

There are many more examples of mixing - and , in older DAs like e.g. SPN 1214 in 201311. These have mostly all gone away in newer DAs.

This is my best guess at the proper interpretation of those mixed fields. I would love to hear other's opinions too.