# 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
```