JavaVCPU

JV-DOS 1.3

JV-DOS runs as guest bytecode. It provides a shell, persistent named files, an editor, JVS interpretation, COM loading and small media viewers. Commands and filenames should be uppercase. Click the VM window before typing.

Command help (HELP)	Directory (DIR)

Command	Purpose / example
HELP, CODEHELP	Shell or programming help
DRIVE, DRIVE N	Show/select a mounted storage device (0-255); resets to bank 2 root
DIR	List the current folder; folders show <DIR>
MKDIR NAME, MD NAME	Create a folder
CD NAME, CHDIR NAME	Enter a child folder
CD .., CD /, CD \	Go to the parent or bank root
RMDIR NAME, RD NAME	Remove an empty child folder
TYPE NAME, CAT NAME	Print file contents directly
VIEW NAME, MORE NAME	Read a document with navigation
WRITE NAME TEXT	Create or replace text
APPEND NAME TEXT	Append text to an existing file
EDIT NAME	Create/open a file in the editor
COPY OLD NEW	Copy to a new name
REN OLD NEW	Rename to an unused name
DEL NAME, ERASE NAME	Delete a file
SAVE NAME HEX	Create binary content from uppercase hex byte pairs
RUN NAME	Interpret text, load bytecode, or open image/music by type
IMAGE NAME, SHOW NAME	Display a palette image
PLAY NAME	Play a MIDI-note stream
PRINT TEXT, ECHO TEXT	Print literal text
CLS, CLEAR	Clear display
VER, MEM	Version and memory/file limits
SOUND ON, SOUND OFF	Enable/disable keyboard clicks
BEEP	Short tone
REBOOT	Restart the resident guest boot routine
EXIT	Halt the CPU

Each disk bank provides 255 shared blocks. Names have up to 12 characters. Files use one or more linked blocks and can hold up to 61,200 bytes, subject to available bank space. Folders can nest and share the bank?s block pool; each folder consumes one block. Names are unique within a folder, so different folders can contain files with the same name. File commands accept a single name in the current folder; navigate with CD instead of supplying a multi-component path. DEL and other file commands reject folders; use RMDIR after removing their contents. The CLI and source reader have a 100-character line limit; use Workshop to import longer documents or binary files. COPY/REN report DESTINATION EXISTS if the target name is taken.

Editor and viewers

EDIT DEMO.JVS opens the guest source editor. Arrow keys move; Home/End navigate the line; Backspace and Delete remove characters; Enter inserts a newline; Tab indents. Esc saves and leaves. It is not a cancel operation. The editor highlights source text.

The document pager uses Up/Down, Page Up/Page Down, Space/Enter and Home; Esc closes it. Image viewing closes with Esc, Enter or Q. Esc stops music and silences its voices. A running JVS program checks for Esc between statements.

Source editor	Document pager

Palette image	Music playback status

The screenshot gallery also shows startup, programming help and program execution.

RUN dispatches image/music from their file type, interprets type-1 text, and otherwise validates and loads raw bytecode. It also heuristically treats binary content starting with printable bytes 32-90 as source. The supplied COM starts with opcode 2 to avoid that ambiguity. Filename extensions alone do not define the execution format.

See JVS programming, COM programming, and Tooling and Disk Workshop.

Disk banks (JV-DOS 1.3)

The disk has 254 file banks, numbered 2-255, with 255 blocks shared by all files in each bank. BANK shows the selected bank. BANK + and BANK - move one bank at a time and stop at the boundaries. Reboot returns to bank 2. Existing files remain in bank 2; no disk conversion is required. All file commands use the selected bank and current folder, and COPY/REN stay within that folder. Changing banks resets the current folder to root. Reboot also resets the folder to root while preserving folders and files. Larger files consume multiple blocks; small files retain their existing layout.

The backing hard drive remains 16 MiB because the CPU uses a three-byte disk address. DOS now uses most of that space through linked file blocks. The Java DOS image assembler lives in xyz.ignite4inferneo.jvdos; CPU and device code remain in xyz.ignite4inferneo.

The editor buffers files in RAM bank 1, supports 16-bit cursor positions, and commits on Esc. When the bank is full, the existing disk file stays unchanged and the editor retains its buffer for shortening and retrying. TYPE/VIEW, COPY, APPEND, REN, DEL, JVS RUN and COM RUN support linked files.

Shell history and completion

At the DOS prompt, Up recalls older commands and Down moves toward newer commands. The last 16 submitted, nonempty interactive lines are kept until reboot. Moving Down past the newest entry restores the line you were drafting, including its cursor position. Recalled commands can be edited and submitted again. JVS statements and editor text are not added to history.

Tab completes the word at the cursor. Repeated Tab cycles matching command names, or names in the current folder of the selected disk bank for file-command arguments (including both COPY/REN filenames). The rest of the input line is preserved. A completed final word receives a trailing space. Unmatched prefixes and replacements that exceed the 100-character line limit leave the line unchanged. Typing or moving the cursor starts a new completion search. In EDIT, Up/Down still navigate the document and Tab inserts four spaces.

Reading the kernel source

src/main/java/xyz/ignite4inferneo/jvdos/JvDosImage.java describes guest instructions with named OPCode values, one emitted instruction per line. Asm.emit checks operand counts before encoding bytes. Labels and the get/put, call/ret and file-buffer helpers hide address fixups and state layout.

A-D hold working values, E/F support existing addressing sequences, and G/H implement far branches and the COM entry stubs. I/J handle indirect RAM reads without overwriting A-H. K/L hold glyph pixel coordinates, avoiding temporary RAM writes during rendering. M-P are available for future routines. Helpers can overwrite their documented scratch registers; guest JVS variables A-P live separately at bank 0, page 252, offsets 224-239.

The register parser converts letters A-P directly into variable indices. RUN clears all sixteen JVS variables. Existing COM entry points and disk file layouts are unchanged. System-image revision 13 triggers installation of the updated kernel on next startup while preserving user files.

Folder storage

The existing file headers and linked data blocks retain their layout. Directory headers use type 4, zero length and no continuation. The reserved page 255 in each file bank stores parent IDs at offsets 1-255, indexed by head slot plus one. ID 0 means root; other IDs identify a directory slot plus one. Offset 0 retains the existing initialization marker. Existing flat images have zero parent metadata and open as root files without conversion. Directory entries and file data share the 255 allocatable blocks; continuation ownership validation still covers the entire bank.

For example:

MKDIR DOCS
CD DOCS
WRITE NOTES.TXT HELLO
MKDIR DRAFTS
CD DRAFTS
WRITE NOTES.TXT DRAFT
CD ..
DIR
CD /

Additional disks are mounted with program arguments such as --disk=1=secondary.img. Each has independent banks and folders. The guest TCP network controller and sample program are described in Peripheral buses.