Dumb

The world's dumbest dumb terminal.

I wrote this while developing an ARM based product for a company in England about 17 years ago. I needed to talk to the target on an RS-232 connection and download a bootstrap program using the XMODEM protocol (this was dictated by the processor firmware when it did not find a bootloader on first power on). Use of XMODEM was and is pretty common in embedded environments, partly for its simplicity.

Try as I might I could not get any of the usual terminal emulators with XMODEM support to work. I figured that since the various Unix/Linux terminal programs already did the terminal emulation part, what I really needed was a Telnet/SSH style program that worked over a tty. The cu program that is part of UUCP would have been about right, except that there is no XMODEM capability, so I wrote this. Unlike cu it does not fork an extra process.

Even now for most embedded system downloads, it has proven more reliable than the more sophisticated terminal programs, across a range of target microcontrollers.

Build

Dumb should compile without problem on any system with poll() and termios. There is also support for GNU readline. To compile (it's hardly worth even providing a build system for this):

$ gcc dumb.c -lreadline -o dumb

or without readline support

$ gcc -DNOREADLINE dumb.c -o dumb

and copy the result to $HOME/bin or wherever you see fit!

Usage

$ dumb [options]

Options

• -t --- prepend responses from target system with a timestamp.
• -h file --- set the history file name for GNU readline (default: .dumb).
• -l tty --- set the tty for the target system (default: /dev/ttyS0).
• -b baud --- set the baudrate (default: 115200).
• -e ch --- set the escape character; specify a numeric value or ^x notation (default ^A).

Dumb copies all input to the remote and all output from the remote is echoed to the terminal. When the escape character is entered, dumb breaks out of normal operation and executes a command depending on the next character as follows:

• ^A (or current escape character) --- send character to remote.
• t, T --- toggle timestamp in prompt.
• c, C --- switch to command mode.
• s, S --- XMODEM send
• h, H --- browse history
• x, X --- exit dumb.

Command Mode

Switching to command mode ^Ac issues a prompt and reads a single command from the console and executes it using sh -c. The command is added to the history file.

XMODEM Send

Switching to XMODEM send mode ^As issues a prompt and reads a filename. The filename is added to the history file. Dumb then starts the XMODEM transfer to the target system. It displays a simple spinner and percentage complete during the transfer.