JunkTerm
========
JunkTerm provides a monochrome Linux text terminal on a cheap e-paper. This is
an experimental and unorthodox way of using e-paper, and may/will shorten its
lifespan, and/or damage it easily, so CAVEAT EMPTOR.

Software dependencies
---------------------
External dependencies are minimal.
  Build-time: Just some basic Linux development environment (with modern
binutils, GCC, sh and GNU Make). The software was originally developed natively
on Raspberry Pi OS.
  Run-time: Besides the Linux kernel (with SPI and GPIO support), the software
assumes /bin/sh and glibc.

Supported hardware
------------------
Currently only a single fixed hardware setup is supported. The software is
unable to probe the hardware, so if you run it in a random system with a wrong
e-paper panel or cabling, then some permanent damage may occur.
  E-PAPER PANEL			DRIVER BOARD			HOST COMPUTER
WFT0583CZ61 (5.83", 648x480)	Waveshare E-Paper Driver Hat	Raspberry Pi

Usage and operation
-------------------
Build with "make".
  Run with "junkterm". The only supported option is -d which enables debug
prints (currently shows only e-paper wait/refresh times to help with
optimizations).
  On startup the program clears the e-paper, then prints a banner message and
launches the shell with output directed to the e-paper. The input is taken from
the launching terminal.
  The main loop waits for user input, passes it to the shell and then prints
the session output on the e-paper. The display is powered only during the
refresh. Refresh is done once the input and output has settled. Any input will
switch to fast refresh (1 second) interval, then next refresh is after 5
seconds. When there is only output from shell, the refresh interval is 30
seconds.
  Refresh is by default done in partial/fast mode (1 <= second). Once an hour
there is a full slow refresh (several seconds, depends on the e-paper). Full
refresh can be triggered also by Ctrl-L.
  The program terminates once the shell exists. Abnormal exit can also occur
after a system call failure etc.
  On exit the program attempts to clear the display, put it in deep sleep and
turn the power off. Since this is just an userspace program, it cannot be
guaranteed that the exit sequence is successful or complete. So better not to
run this program unattended without an user visually observing that everything
went OK.

Terminal emulation
------------------
The terminal declares itself as "vt102". It supports 80x24 and 132x24 modes
and emulates a subset of VT102 sequences. The font is CP437 8x16 VGA font.
Currently the terminal dimension is fixed and the screen is then squeezed or
strectched to fill the e-paper. This is a crude way and for optimal picture the
e-paper needs to be near 640x480 and 4:3.
  Currently the emulation is sufficient to run basic terminal programs (e.g.
GNU Screen or VIM). The following vttest tests are passing:
  1. Test of cursor movements

License
-------
This is free software released under the 0BSD license. See included LICENSE.