Slides from my PyWorks 2008 talks are now available. This conference was shared with php|works and I enjoyed this format. It was great to see many of my Python and PHP friends at the same event. Thanks to everyone who attended my talks.

Py65: Microcontroller Simulation with Python

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This talk introduced the venerable 6502 microprocessor family, building small computer systems with these parts, and then simulating those systems with Py65.

The audience participation was great. We had fun stepping through some small assembly language programs on the simulator. One attendee wrote:

This was fascinating and the speaker was awesomely enthusiastic. The overview of microcontrollers and their significance was enlightening and entertaining. The simulator design presented was fantastically simple and very Pythonic. I can’t wait to see where this project goes.

Thanks and I’m glad you enjoyed it. For updates on the Py65 simulator, please watch my blog and the Py65 project page on Ohloh.

URL Mapping with Routes

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We explored the Routes library from the ground up, setting it up and then exploring its options and matching. We worked through many of the examples with live demos on the Python interactive interpreter.

The talk was attended by several Pylons users, who gained a better understanding of how Routes works by seeing it outside the context of any particular web framework.

URL Mapping with Horde/Routes

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Bonus Slides! Horde/Routes is a PHP 5 library that is a direct port of Routes. Since there were so many PHP folks at this conference as well, I ported all of the examples in my Routes talk to work with Horde/Routes.

These slides will help you get acquainted with the PHP version. Since the two presentations are otherwise identical, you might also find it an interesting comparison between Python and PHP 5.

Py65 0.1, a 6502 microprocessor simulator written in Python, has been released and is available on the Python Package Index (PyPI). You can now easy_install it:

$ easy_install py65

Py65Mon

Since my initial announcement of Py65, there have been many bug fixes and unit tests added. The most noticeable addition is a new machine language monitor. It will be installed automatically and is started with the py65mon command:

$ py65mon
 
Py65 Monitor
 
<6502: A=00, X=00, Y=00, Flags=20, SP=ff, PC=0000>
.

At the prompt, type help for a list of commands or help command for help on a specific command. The monitor commands are very similar to the excellent VICE Monitor, so VICE users should feel right at home.

The biggest difference from VICE is that the load command requires a load address as the second argument and starts reading the binary data from byte 0. It does not expect byte 0 and 1 of the file to contain a Commodore-style load address. Also, assembling and disassembling from the monitor are not yet implemented but are planned.

Hello World

Just like Michal Kowalski’s 6502 Macroassembler & Simulator for Windows, Py65Mon will trap writes to $E001 and echo the bytes to STDOUT.

This is enough to get us to our first “Hello World” program running under Py65. First, we’ll write a short assembly language program to print the message. Save it as hello.asm.

*=$C000
CHAROUT=$E001
 
HELLO:
  LDX #$00
LOOP:
  LDA MESSAGE,X
  BEQ DONE
  STA CHAROUT
  INX
  JMP LOOP
DONE:
  RTS
 
MESSAGE = *
  !text "Hello, World!"
  !byte 0

We then assemble the program into a binary, using Marco Baye’s Acme Cross-Assembler:

src$ acme --format plain --outfile hello.bin hello.asm

The --format plain switch instructs Acme not to prepend the Commodore-style load address in the binary. If you’d like to get going quickly, you can also download hello.bin.

With the binary ready, we can start the monitor and load it in:

src$ py65mon
 
Py65 Monitor
 
<6502: A=00, X=00, Y=00, Flags=20, SP=ff, PC=0000>
.add_label c000 hello
 
<6502: A=00, X=00, Y=00, Flags=20, SP=ff, PC=0000>
.load "hello.bin" hello
Wrote +29 bytes from $c000 to $c01c

Py65Mon supports symbolic addressing in most commands. The first command, add_label, defines hello as a label for address $C000. The second command loads the binary into that address.

We can now set the program counter with the registers command, and execute the code up to RTS with the return command.

<6502: A=00, X=00, Y=00, Flags=20, SP=ff, PC=0000>
.registers pc=hello
 
<6502: A=00, X=0d, Y=00, Flags=20, SP=ff, PC=c000>
.return
Hello, World!
<6502: A=00, X=0d, Y=00, Flags=20, SP=ff, PC=c00e>
.

Now we have run the program, printed “Hello, World!”, and returned to the prompt. We can see the program counter is left at $C00E.

You can also use the step command to step through the program. Just set the program counter to the start address again ($C000 or hello) and repeatedly enter step. As you are stepping repeatedly, you can simply hit ENTER to repeat the last command.

From here you can also explore other commands, e.g. mem c000:c003 to display the memory in that address range. The default radix is hexadecimal. You can also prefix with $ for hexadecimal or + for decimal, like mem +49152:+49155.

Next Steps

Py65 and its monitor are now complete enough to run most simple 6502 programs, including many from the 6502.org Source Code Repository. The next versions will include more I/O devices and monitor commands, with the goal of running a sophisticated 6502 program like Lee’s Davisons’ Enhanced 6502 BASIC.