While validating that device serial1 was really a serial port
Using the raspbian-jessie-lite image dd 2016-02-26 (and performing all updates after that), I can't get the serial console working on a RPi 3.When I put the image in a RPi 2, everything is fine.But whether the console is named 'serial' or 'tty AMA0', if you check /proc/cmdline, both are changed to 'tty S0'[email protected] I was surprised that I couldn't find a standard DT mechanism for giving serial ports a chosen name.
The latest rpi-update firmware fixes that issue, but you can avoid it by using core_freq instead of gpu_freq. After I reached all new default settings, everything kept working.It may be possible to ameliorate the issue by automatically reprogramming the uart clock divisor when the core clock changes, but that will depend on there being a suitable ratio between the overclock and the minimum.Therefore the only way to be sure that the baud rate doesn't ever change is to set core_freq to minimum to start with, which is 250MHz.By not working, I mean that I mostly get garbled output and I am unable to use my keyboard to interact with the system.There is a forum thread about it and (apparently) someone found a workaround ...
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My theory is that, pre-kernel-boot, something needs to set some frequencies, reads them out of the config.txt, and if not present, uses the (old) defaults. Another thing that is probably done there, is 'patching' the kernel's commandline parameters: file 'cmdline.txt' now contains 'console=serial,115200' instead of 'console=tty AMA0,115200'.