DVX_GUI/termdemo

SecLink Terminal Demo

Standalone DOS terminal emulator combining the DVX windowed GUI with SecLink encrypted serial communication. Part of the DVX GUI project.

This is NOT a DXE app -- it is a freestanding program with its own main() that initializes the DVX GUI directly and manages its own event loop. Unlike the DXE apps (progman, notepad, clock, dvxdemo) which run inside the DVX Shell, this program demonstrates how to use the DVX widget system outside the shell framework.

Connects to a remote BBS through the SecLink proxy, providing a full ANSI terminal in a DVX-style window with encrypted transport.

Architecture

termdemo (DOS, 86Box)
    |
    +--- DVX GUI           windowed desktop, ANSI terminal widget
    |
    +--- SecLink           encrypted serial link
    |      |
    |      +--- packet     HDLC framing, CRC-16, Go-Back-N ARQ
    |      +--- security   DH key exchange, XTEA-CTR cipher
    |      +--- rs232      ISR-driven UART I/O
    |
  COM port (86Box emulated modem)
    |
  TCP:2323
    |
  secproxy (Linux)
    |
  TCP:23
    |
  Remote BBS

All traffic between the terminal and the proxy is encrypted via XTEA-CTR on SecLink channel 0. The proxy decrypts and forwards plaintext to the BBS over telnet.

Usage

termdemo [com_port] [baud_rate]

Argument	Default	Description
com_port	1	COM port number (1-4)
baud_rate	115200	Serial baud rate

Examples:

termdemo                  # COM1 at 115200
termdemo 2                # COM2 at 115200
termdemo 1 57600          # COM1 at 57600
termdemo -h               # show usage

Startup Sequence

1. Seed the RNG from hardware entropy (PIT-based on DOS).
2. Open SecLink on the specified COM port (8N1, no handshake).
3. Perform DH key exchange (blocks until the proxy completes its side).
4. Initialize the DVX GUI (1024x768, 16bpp VESA).
5. Create a resizable terminal window with menu bar and status bar.
6. Register an idle callback so serial data is polled during GUI idle.
7. Enter the main loop.

The handshake completes in text mode before the GUI starts, so the DOS console shows progress messages during connection setup.

Main Loop

Each iteration:

1. secLinkPoll() -- read serial data, decrypt, deliver to ring buffer.
2. dvxUpdate() -- process mouse, keyboard, paint, and window events. During paint, the terminal widget calls commRead to drain the ring buffer and render new data.

An idle callback also calls secLinkPoll() so incoming data is processed even when the user is not interacting with the terminal.

Data Flow

BBS -> proxy -> serial -> secLinkPoll() -> onRecv() -> ring buffer
    -> commRead() -> wgtAnsiTermWrite() -> ANSI parser -> screen

Keyboard -> widgetAnsiTermOnKey() -> commWrite()
    -> secLinkSend() -> serial -> proxy -> BBS

A 4KB ring buffer (RECV_BUF_SIZE) bridges the SecLink receive callback (which fires asynchronously during secLinkPoll()) and the terminal widget's comm read interface (which is polled synchronously during the widget paint cycle). This decoupling is necessary because the callback can fire at any time during polling, but the terminal widget expects to read data synchronously.

GUI

• Window: resizable, titled "SecLink Terminal"
• Menu bar: File -> Quit
• Terminal: 80x25 ANSI terminal widget with 1000-line scrollback
• Status bar: shows COM port, baud rate, and encryption status

The ANSI terminal widget supports standard escape sequences including cursor control, SGR colors (16-color CGA palette), erase, scroll, insert/delete lines, and DEC private modes (cursor visibility, line wrap).

Test Setup

1. Start the SecLink proxy on the Linux host:

   secproxy 2323 bbs.example.com 23
   

2. Configure 86Box with a COM port pointing at the proxy's listen port (TCP client mode, port 2323, no telnet negotiation).

3. Run the terminal inside 86Box:

   termdemo
   

4. The handshake completes, the GUI appears, and BBS output is displayed in the terminal window.

Building

make            # builds ../bin/termdemo.exe (and all dependency libs)
make clean      # removes objects and binary

The Makefile automatically builds all dependency libraries before linking. Objects are placed in ../obj/termdemo/, the binary in ../bin/.

Target: DJGPP cross-compiler, 486+ CPU, VESA VBE 2.0+ video.

Dependencies

All libraries are built into ../lib/:

Library	Purpose
libdvx.a	DVX windowed GUI and widget system
libseclink.a	Secure serial link wrapper
libpacket.a	HDLC framing and reliability
libsecurity.a	DH key exchange and XTEA cipher
librs232.a	ISR-driven UART serial driver

Files

termdemo/
  termdemo.c       terminal emulator program
  Makefile         DJGPP cross-compilation build