Example programs

Example programs

The repository includes editable source and generated bytes under examples/. Rebuild the byte listings from the project root:

powershell -ExecutionPolicy Bypass -File examples/build.ps1

The script strips # comments, converts two-digit hex to bytes, and enforces the one-page bare-metal and 61,200-byte DOS file limit. It is a hex converter, not a mnemonic assembler.

Bare metal

The default launcher always executes the disk boot flow. To experiment, temporarily replace DiskInstaller.boot(); inside Main.main() with:

byte[] program = java.nio.file.Files.readAllBytes(
        java.nio.file.Path.of("examples/bare-metal/ANSWER.bin"));
System.arraycopy(program, 0, Memory.getMemoryPage((byte) 0), 0, program.length);
REGISTERS[Registers.PAGE.address()] = 0;
REGISTERS[Registers.COUNTER.address()] = 0;

Build and run Main with JDK 26 from the project root. Device/disk initialization still runs, but BIOS and DOS are not executed. Change the path to select another example; restore the original boot call afterward. Restore the original boot call when returning to JV-DOS; this is a source-level experiment rather than a launcher option.

Source / binary	Behavior
bare-metal/ANSWER.hex / ANSWER.bin	6 times 7; prints 42 in host console
bare-metal/COUNT.hex / COUNT.bin	Prints 0 through 4, then halts
bare-metal/PIXEL.hex / PIXEL.bin	Clears screen, draws white pixel at (128,128), displays it
bare-metal/MEMORY.hex / MEMORY.bin	Writes 42 and a six-byte code tail to page 1, jumps there and prints 42

ANSWER's complete bytecode is:

02 06 00  # STORE 6 A
02 07 01  # STORE 7 B
14 00 01 02  # MULTIPLY A B C
05 02     # OUTPUT C
04        # STOP

COUNT places its loop at byte 6 and STOP at byte 16. MEMORY demonstrates STORE_MEM_ON_PAGE and CHANGE_PAGE_JUMP, constructing its destination code before transferring control. These examples finish with CPU STOP; close the display window afterward.

DOS source and COM

Import the following through Workshop into an initialized disk, download it, install it while the VM is stopped, and restart with normal DOS boot code:

File under examples/dos/	DOS command	Result
HELLO.JVS	RUN HELLO.JVS	Greeting, beep, prompt
MATH.JVS	RUN MATH.JVS	42 then 0
COUNT.JVS	RUN COUNT.JVS	0 through 4 then DONE
HI.COM	RUN HI.COM	HI, newline, prompt

HELLO's source is:

PRINT HELLO FROM JV-DOS
BEEP
END

EDIT HELLO.JVS opens it in the guest editor; Esc saves. The JVS programming page includes the complete math and counting listings. The COM programming page explains HI's character calls and return ABI. Import HI.COM, not HI.hex.

Workshop's Add sample files also provides a document, image and tune. See Tooling and Disk Workshop for the disk exchange workflow.

Built-in graphics demos

The Programs loader also includes these display examples. Select the corresponding Programs.Program with Programs.load(...) in place of the normal boot call when experimenting.

DISPLAY_HELLO_CPU	SNOWFALL

These two built-in demo captures predate the October 22 guest screenshot refresh; they illustrate the selected demos rather than the current DOS shell. The complete screenshot gallery includes current DOS and JCTRL application views.

JCTRL examples

Startup bundles JCTRL, TextEdit and Paint. WEB and Pong are optional imports into a JVFS folder with free space; DRIVE-/DRIVE+ selects mounted disks in Files. Import .COM files with Workshop, download the disk, restart, and open them from JCTRL Files.

Gradle task	Program / purpose
paintExample	examples/jctrl/PAINT.COM, palette painting and native JI save/load
textEditExample	examples/jctrl/TEXTEDIT.COM, windowed text/hex editor
browserExample	examples/jctrl/WEB.COM, HTTP text browser and optional HTTPS gateway
jctrlExamples	examples/jctrl/PONG.COM, mouse-controlled game
desktopInstaller	examples/jctrl/JCTRLSET.COM, fullscreen DOS bundle setup

See JCTRL applications for controls and Installers for setup and portable transfer commands.