Serial console speed and key mappings/bindings problem (only within bootloader env)

I'm still relatively new to this so apologies if the answer is obvious, but I wanted to ask if I should be changing any settings on my serial console/usb uart device.


  1. when connected to a fritzbox 7490 via serial, I can access the bootloader fine, however Ctrl+C, and backspace keys are not working.
  2. Additionally I noticed a few other oddities where the terminal is unresponsive to input and the display sometimes misses some output on bootup , unless I detach my USB UART, then reconnect it each time before booting.

#1 above is the main reason for creating this thread.

Info Gathered:

  1. I am accessing the USB UART via the screen utility with this commandline:
sudo screen -S test -L -Logfile test-$(date '+%Y%m%d-%H%M%S').txt /dev/ttyUSB0 115200
  1. I've confirmed that the factory firmware is expecting 115200 baud:
# cat /proc/cmdline 
console=ttyS0,115200n8r nor_size=0MB sflash_size=1024KB nand_size=512MB ethaddr=38:10:D5:xx:xx:xx
  1. Possible cause for Issue#1 perhaps- I noticed by chance two parameters in the eva bootenvironment settings that imply bootloader is expecting (or needs?) different serial parameters. Whats the best way to deal with this? Should I be launching a separate screen session when I need to interact with the bootloader? Can these settings typically be modified - or is that potentially dangerous to do?
modetty0              38400,n,8,1,hw
modetty1              38400,n,8,1,hw

screen should let you change the serial settings on-the-fly. ^a h as I recall to get help screen up.

Thanks @jeff , I had a hunt around but so far can't find anything to change baud speeds on the fly within screen.

In any case I tried several different screen settings separately from launch, and so far they all just show gibberish in the console.. Seems the "modetty0/1 38400..." settings are either unused on 7490 or not related to serial connection.. The only way the serial console shows/does anything meaningful is with baud set to 115200 .

Any other ideas why the Backspace key and Ctrl+ "anything" doesn't do anything? Is it just a limitation of the evm bootloader minimal shell/environment?

You're right, I don't see the ability to change baud rate in screen (from pyserial) can definitely change on the fly:

--- Port settings (Ctrl+T followed by the following):
---    p          change port
---    7 8        set data bits
---    N E O S M  change parity (None, Even, Odd, Space, Mark)
---    1 2 3      set stop bits (1, 2, 1.5)
---    b          change baud rate
---    x X        disable/enable software flow control
---    r R        disable/enable hardware flow control

As to why your boot loader isn't responding to control characters, I don't know. I've never expected boot loaders, modems, or the like to take much more than printable ASCII characters, space, return, and maybe a delete character (without any expectation that it is DEL or BS for the device).

A couple references I found, though not obviously helpful on your specific question:

Yeh i’m thinking that its just a limitation . Thanks for the ideas tho.

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