On Thu, Oct 26, 2023 at 12:20:08PM -0400, Morgan Aldridge wrote: > Yes, your assumption was correct, every keypress acts as if I had pressed > enter. Thanks for confirming!
Getty re-displays the login prompt when it sees either 0x00 or 0x80 on the serial line. In fact, you can do it from the normal framebuffer console too, just hit control-@ at the login prompt and it should repeat. (This is a historic behaviour which was once used for semi-automatic baud rate selection where you hit 'BREAK' a few times to get the remote end to cycle through all the speeds it supported until you, (hopefully), got a login prompt). So in your case, it seems that either the terminal is putting something on the serial data lines that the USB serial adaptor is interpreting as nulls, or possibly it's doing something with the handshaking lines that makes the USB serial adaptor generate the equivalent internally. Any extra nulls added as padding bytes probably wouldn't show up in the loopback test either, because the terminal would just happily ignore them.
