tracked down another issue with BPI/RCM4. i was wondering why the ethernet was working only at 100mbit/s and not reliably. turns out it had to do with the connection/polarity of the LEDs. the bpi-cm4 expects LED1 to be active high, but on the Reform motherboard, it's wired as active low. and: the LED pins also double as config straps for the RTL8211F PHY on the bpi-cm4. so one or two config bits must have been unexpected. cutting the traces on RCM4 made 1gpbs work for the first time.
all ethernet LEDs are specced as active low in the raspberry pi cm4 manual. sigh. pondering how to solve this incompatibility with bpi cm4
idea: XOR gate driven by a GPIO that is set/unset by software depending on rpi or bpi
Ok without looking it up that is an XOR gate or eXclusive OR ?
:0 I can't remember the truth table off hand but I think it is something like
0 - 0 - 0
1 - 0 -1
0 1 1
1 -1 -1
so output high when either of the inputs are high AND both inputs are high.
Nearly right, not bad given I have not bad given I have not really looked at this stuff for years.
Thanks
@zleap yes