> On 01 Aug 2016, at 16:20, Stephen Warren <swar...@wwwdotorg.org> wrote: > > On 07/29/2016 03:49 PM, Alexander Graf wrote: >> On the raspberry pi, you can disable the serial port to gain dynamic >> frequency >> scaling which can get handy at times. >> >> However, in such a configuration the serial controller gets its rx queue >> filled >> up with zero bytes which then happily get transmitted on to whoever calls >> getc() today. >> >> This patch adds detection logic for that case and disables the mini uart if >> it >> sends a zero byte during probe. That way we can leave the driver enabled in >> the >> tree and can determine during runtime whether serial is usable or not. > > I don't think this is the correct approach; it is quite possible and legal to > receive a NULL character (which with this HW IIRC can also be triggered by a > break condition on the line) even when the UART is fully operational. This > could lead to false detection, and end up disabling the UART when it should > not.
Right, that’s why I tried to be very careful about the detection and only have it triggered when the very first byte ever received is a null byte. Any bytes after that don’t affect it. > Rather, I would suggest detecting this condition based on some register > content. The most direct might be to check the pinmux for the UART's RX pin, > or perhaps whether the UART itself has been initialized. Hmm. I can try and dig through the documentation again to see whether there is a way. Alex _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
