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Sorry to dig out such old stuff, but did you get any further with playing with the ID pin on the micro USB connector? I've just read PMIC datasheets - does the KPW really use the MC34708? I'm asking because the kernel on a running device reports a MC13892 instead. But the latter is not plausible on a i.MX50 device - maybe just re-used old code from the i.MX35 devices on the software side.
I'd be interested in whether the UART pass-through would work when it really is a MC34708 (and the cited uboot code seems to indicate that). The "factory mode" seems to be related to powering only (and the ID pin is pulled high for that, see ). The UART modes however seem to be triggered by pulling the ID pin low with a 150 kOhm resistor (table 95 in the MC34708 datasheet). For general circuit of UART operation, see figure 30. Then there are also the JIG UART cable resistance values.
Well, maybe I need to do a lab weekend myself.
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