VM02 Beta 1

[David Schmenk <dschmenk@YUCH.gmail.com>]

Whoopee, time to release a Beta!  This is a pretty significant upgrade
to the Alpha release.  A few VM bugs were fixed that were exposed by the
new functionality.  Performance of Java calls back into the VM and
device calls has been improved.  A new device driver architecture has
been implemented and has three drivers available: console, super serial
card, and mouse card.  The mouse card uses the VBL interrupt for
accurate timing.  I wrote a simple multi-threaded terminal program to
test the serial port.  I discovered that the mouse firmware had such
high overhead it caused characters to be dropped at 9600 baud.  The only
workable solution was to add a control to the mouse driver to totally
disable and remove the IRQ handler.  On the IIc, the VBL interrupt would
also confuse the game paddle code - they share an I/O location between
the mouse and game controller.  So again, I needed to disable the VBL
interrupt to consistently read the paddle on the IIc.  Not the kind of
stuff you run into programming the Apple II in everyday environments.

I also added parameter passing.  If your launcher supports it, you can 
pass in a complete command line.  Something like:

JAVA.SYSTEM ECHO HELLO WORLD

would pass HELLO and WORLD as parameters to the ECHO class.  The test 
launcher (davex) I used only allowed for one parameter though - the 
class to execute.

When the program exits, it will offer the option to reboot or return to 
the VM02 command line and run another class.  Kind of a compromise 
between a nice exit back to ProDOS and running more Java classes.

I'm quite pleased with the progress made in this release.  I feel the
VM02 environment is shaping up to be one of the most powerful and full
featured environments for the Apple II.  I hope you take some time to
check it out.  All suggestions welcome,

Dave...

Get it here:

http://schmenk.is-a-geek.com/tarfiles/VM02BETA1.DSK.zip

From the README:

VM02 Java capable Virtual Machine for Apple II
==============================================

Introduction:
-------------
VM02 is a Java compatible environment for the Apple II series of computers.
Most basic features of a Java VM are implemented to allow direct
execution of
standard Java class files. However, in order to fit in the constraints of a
64K, 8 bit, 1 MHz computer, some aspects of a JVM have been reduced or
removed.

What is implemented:
- Standard Java class file loading and execution.
- Full object inheritence
- Multithreading (4 threads max by default)
- Exception handling
- Arrays up to 15 dimension
- 32 bit integers and single precision floating point
- Garbage collection
- Finalizers
- Software and hardware implemented timing
- Device drivers for common hardware

What is missing:
- 64 bit data types unimplemented
- Standard class library unavailable or limited implementation only
- Lots of memory

Running VM02:
-------------
VM02 is run by executing the JAVA.SYSTEM file. You must start
JAVA.SYSTEM from
the prefix where it exits. This is required to find the class base path
to the
support classes. Parameter passing is supported if your shell
implements it.
If no paramter is passed in and a file named STARTUP exits, it will be
loaded
as the initial class. Otherwise, you will be greeted with with a prompt to
type in the class name to execute. You can start classes in other
directories
by typing in the fully qualified path. Class filenames under ProDOS are
missing
the ".class" suffix due to limited filename lengths. For example, to
execute
the Hello.class file on the VM02.SAMPLES volume, with VM02 you would type:

/VM02.SAMPLES/HELLO

at the "Main class:" prompt. You would see this:

Main class:/VM02.SAMPLES/HELLO

and then VM02 would attempt to find and load the class file. If an error
occurs along the way, you will get an Unhandled Exception message, probably
because the file (or superclass file) was not found. The preferred
directory
structure is to place all classes as subdirectories of the main VM02
directory.

Implementation of VM02:
-----------------------
VM02 is implemented from scratch in 6502 assembly, optimized for the
6502 and
Apple II platform. The entire VM fits in about 20K of RAM. This leaves
about
30K of RAM available for data and code. Not a lot, but Java was defined for
small platforms so you can get some reasonable programs even in such a small
space. A high-resolution graphics page is available for use with small
programs. Performance is acceptable for a 1 MHz, 8 bit CPU. On par
with the
UCSD p-System VM used in Apple Pascal. All features of the Apple II are
made
available through either specific classes, a low-level class that can
call ROM
routines, or both. There is a device driver architecture that currently
supports 80 column cards, the Super Serial card, and the Apple Mouse
card. Lastly, native methods are available through an overly complicated
process.

As noted earlier, class filenames are missing the ".class" suffix. System
classes are in the JAVA/* subdirectories. Apple II specific classes are
found
in the APPLE2/ directory.

Developing for VM02:
--------------------
There isn't a native Java compiler for the Apple II (yet). All Java source
must be cross-developed on a capable computer. The resulting class file
needs
to be transferred to an Apple or emulator using any number of available
tools.
One way is to use a tool like a2tools, AppleCommander, or CiderPress to copy
the class file to a .DSK disk image file. The disk image can be run
directly
from an emulator or copied to real hardware with ADT or ADTPro. To compile
against the Apple II specific classes, either download the source
package (you
will also need cc65, a 6502 C compiler package) or copy the APPLE2/
directory
contents and rename the files with mixed case and add the .class suffix.

The sample classes:
-------------------
Included with VM02 are sample classes that show off the capabilites of the
environment. They can be executed from the samples disk or copied to
another
location.

HELLO - A simple text entry program
HELLOWORLD - sample multi-threaded program
MOIRE - Hires example, requires AppleSoft in ROM
HIRESDEMO - Another hires demo
RODSCOLORS - Lores demo
SIMPLEPONG - Lores demo with paddle input
TERMINAL - Simple terminal program using the SSC
LIST - list a text file to the screen
P8 - ProDOS example
APPLE2/MOUSE - AppleMouse class with interactive test


Beta1 release:
--------------
This represents the first Beta release of VM02. All the VM functionality
is in
place.  Some support classes may be extended or implemented to add compiler
features or improve compatibility.  This is pretty solid for small
programs but
Java is a large and rich environment.  No doubt there will be many
issues crop
up.

Known issues:
-------------
Currently two know issues are exist; the StringBuilder class has
problems that sometimes
cause string concatenation to freak out. I'll be looking into this
shortly. In
the mean time, try alternative methods (like individial print() calls to
print
a compound message). The Super Serial Card driver has problems with
XON/XOFF
flow control. It might be a problem with my USB serial dongle. I tried
hardware flow control, which worked except charaters would get truncated
when
it halted the receiver. XON/XOFF should work, but doesn't on my setup. I'll
try to connect to a real serial port on a Linux box to see if it works any
better.

Dave Schmenk...