[Gmecm] $58 A/F logic

[Rob Handley]

Found a bit of logic in the A/F calculation of $58 that seems weird to me. 
There's more than one route to it, but it's always downstream of setting 
accumulator A to either: KAFSTCN (stoi), KMAXLEAN, or the F56/F57 look up 
A/F values:

DA01: LDA01 SUBA L000D     ; A = A - A/F time out (from F51 & F52)
DA03:  BCC LDA06     ; If A >= 0 go to LDA06
        ; else...
DA05:  CLRA      ; A = 0

DA06: LDA06 STAA _AIRFUEL_    ; Store A in _AIRFUEL_

I just don't understand why this code appears to be trying to take desired 
A/F down to zero.

Can anybody help?

Rob