support Ford checksums

[incognitojam]

WIP

• Ford checksums are named "SignalName_Cs" and counters are named "SignalName_Cnt"
• The checksum algorithm and byte position changes for each message
• Ford also sometimes has multiple checksums in one message...

example (although I can't see this message on the bus anyway):

BO_ 931 Body_Info_9_FD1: 8 GWM
 SG_ PtWakeReas_D_Stat : 38|4@0+ (1,0) [0|15] "SED"  PCM_HEV
 SG_ VehOnSrc_D_Stat : 19|4@0+ (1,0) [0|15] "SED"  ABS_ESC,PCM_HEV,ECM_Diesel,PCM
 SG_ StrtrMtrCtlDStat_No_Cs : 31|8@0+ (1,0) [0|255] "unitless"  PCM_HEV,ECM_Diesel,PCM
 SG_ EngStrtActv_B_Stat : 39|1@0+ (1,0) [0|1] "SED"  PCM_HEV,ECM_Diesel,PCM
 SG_ EngStrt_B_Rq : 0|1@0+ (1,0) [0|1] "SED"  PCM_HEV,ECM_Diesel,PCM
 SG_ DrvInCtl_B_Stat : 1|1@0+ (1,0) [0|1] "SED"  ECM_Diesel,PCM,PCM_HEV
 SG_ AdvStrt_D_Stat : 23|4@0+ (1,0) [0|15] "SED"  PCM_HEV,ECM_Diesel,PCM
 SG_ CrnkInhbt_No_Cs : 15|8@0+ (1,0) [0|255] "Unitless"  ECM_Diesel,PCM,PCM_HEV
 SG_ CrnkInhbt_No_Cnt : 6|4@0+ (1,0) [0|15] "Unitless"  ECM_Diesel,PCM,PCM_HEV
 SG_ CrnkInhbt_B_Stat : 7|1@0+ (1,0) [0|1] "SED"  ECM_Diesel,PCM,PCM_HEV
 SG_ IgnPreOffActv_B_Stat : 2|1@0+ (1,0) [0|1] "SED"  PCM,PCM_HEV,TCM_DSL

[jyoung8607]

There's been discussions about this sort of thing for other manufacturers where the canonical signal names were known. The most recent I'm aware of is in #633. TL;DR: the fast (and consistent with other ports) thing is to rename your signals, the right thing would be creating support for tagging the existing signals in a to-be-determined manner.