I rigged up a serial console cable today, to try and view some messages during boot. I followed the instructions here:
However, the data that came out was consistently garbled. After a day of debugging, I scoped the TX line. One bit in the send sequence consumes 10.24uS, which works out to a baud rate of 97656 (as opposed to the expected 115200).
I noticed that in the device tree files, there’s a line under tegra186-quill-kernel-4.9.dtsi that sets:
clock-frequency = <480000000>
However since we’re running kernel 4.4, I don’t think that file is included and doesn’t have effect, and we end up with <408000000> . That ratio of increase remains the same at 1.1796x, which seems like a clue that some bug was discovered.
All of this is to say: is there a way to fix this in L4T27.1/kernel 4.4?
I tried to add that frequency specification into the existing kernel’s DTS and recompiled, but it didn’t seem to have the intended effect when I tried.
Is there an injection point that’s recommended?
I initially tried to put it in the tegra186-quill-common.dtsi under serial@3100000 but that didn’t work.