Wednesday, November 25, 2015

Modern micro with RISC OS Pico

RISC OS Pico is a stripped down distribution of RISC OS which turns Raspberry Pi into a modern micro computer. It was created by RISC OS Open Limited to celebrate 50 years of Basic programming language. Imagine a classic BBC Micro manufactured today: the same black and white text console, the same fun and easy to learn programming language, but much cheaper, with much faster CPU and more RAM, with super fast flash storage, capable of fitting into your pocket. This is what Raspberry Pi with RISC OS Pico is.

Pico boots within a few seconds, straight into console Basic interpreter, just like all classic and modern micros. Yes, you heard it right. Micro computers didn't die with the demise of Atari XL/XE, BBC, C64 and Spectrum. There are many modern incarnations, like Micromite Companion, Fignition (using Forth instead of Basic, just like renowned Jupiter ACE), Grant Searle's Multicomp and other homebrew projects. RISC OS Pico has additional advantage, though. Because its shell is BBC Basic VI, it is natively capable of running programs written in BBC Basic. When I was a child I found it very exciting to type in a program printed in a computer magazine and watch it run. Now you can do the same with your kids to teach them programming. You can google around for some ready to use BBC Basic listings or check out the online book and create something yourself. Basic is very easy to learn and great for understanding how the computer works. It lacks many concepts found in other high level languages, like objects, interfaces, first class functions and other stuff, but they have been created for professional programmers, and they don't show you the way the computers really work. For the CPU any program is just a list of instructions (keywords in Basic) located at subsequent memory addresses (line numbers), and the program counter goes over that list one by one, changes the flow when a condition is met (IF...THEN...ENDIF), repeats some instructions in a loop (REPEAT, WHILE) jumps into a subroutine located at different address (GOSUB line-number), then returns from it (RETURN), or jumps to some other place in a program (GOTO line-number). Even threads, when run on a single CPU core, are executed sequentially, it's just very fast switching between them which creates an illusion of parallel processing. This is why people who can program in Basic are able to learn assembly language much quicker than those who come from other languages. Don't be afraid of Basic teaching you "bad habits". Languages are not good or bad, it's programmers that are.

To start using RISC OS Pico you need a distribution which is suitable for your version of Raspberry Pi. If you have model A or B you can use an official ROOL version, otherwise you should download an alternative version, which has been upgraded to work with Raspberry Pi B+ and Raspberry Pi 2. The file is just 4MB and the only thing you need to do is to unpack it to a blank, FAT formatted SD card. You can also buy a ready to use SD card.

When you put the RISC OS Pico on the card and turn the power on, you should see the following prompt on your screen:
RISC OS 192MB
ARM1176JZF-8 Processor
Piccolo Systems SDFS
ARM BBC BASIC VI (C) Acorn 1989
Starting with 97040636 bytes free
>_
The memory size and processor type can be different, depending on the Raspberry Pi model used with Pico. If you see nothing but a blank screen, add the following line to CONFIG.TXT:
hdmi_safe=1
It should solve the video output problem.

Your new BBC Micro is now ready to use, but if you don't have a UK keyboard, you may notice that some keys are mapped differently. To fix his just type in:
*keyboard usa
and press Enter. If you don't use a standard QWERTY layout, replace "usa" with proper country name ("france", "germany", etc). Notice that the aforementioned keyword starts with "*". It's so called "star command", and it's an operating system command called inside Basic - just like DOS command in Atari or Commodore Basics. There are more commands you can use, for example "*cat" lists the contents of a directory, and "*quit" quits from Basic (to go back just type in "basic" and press Enter). Star commands are written in lowercase, unlike Basic keywords, which must be uppercase. You can find star commands reference here.

To load a program from the SD card use the Basic keyword LOAD, for example to load SimonSays program located in Examples folder use the following:
LOAD "Examples.SimonSays"
To list a program use LIST. Press Scroll Lock key during listing to pause screen scrolling, or use "LIST 10,50" to show only lines from 10 to 50.

When you type your own program you can number the lines yourself or use AUTO keyword to let Basic do it for you. To turn off this feature just press Esc. It's a good practice to leave a bit of space between subsequent line numbers (use 10,20,30 instead of 1,2,3) in case you need to put some code between existing lines. But don't worry if you get lost in numbering - just use RENUMBER.

To replace a program line with new code just enter it using the same line number, and to delete it use only the number with no instructions to follow, for example to remove line 10:
10 PRINT "Hello"
type in:
10
and press Enter. Editing lines is also very easy. List the program, press up arrow and find the line you want to modify on the screen, than keep pressing End key. The contents of the line gets copied to the prompt, so you can edit it and then confirm changes with Enter.

When your program is ready you can SAVE it with:
SAVE "filename"
and then execute it with RUN. You can break it at any moment with Esc key. If by any chance the program stops responding, you can restart the Pico pressing CTRL and Break keys simultaneously.

Programs written in BBC Basic are very fast. Even when 8-bit computers dominated the world, BBC Basic was considered the fastest and most mature. I wondered if it's still true, so I created an implementation of the sieve of Eratosthenes in Basic (available here) and Python (available here) using exactly the same algorithm, and run them both on my Raspberry Pi B+. The results are as follows:

InterpreterOperating systemExecution time
BBC Basic VIRISC OS Pico7.84 seconds
BBC Basic VIRISC OS 5.214.59 seconds
Python 2.7.2RISC OS 5.2125.68 seconds
Python 2.7.9Raspbian Jessie17 seconds

To try the BBC Basic version with RISC OS Pico, just put the file "sieve" in the root folder of the Pico SD card, fire up the Pi and do:
LOAD "sieve"
RUN

Wednesday, November 18, 2015

Playing classic games with !ADFFS

!ADFFS is a software written by Jonathan Abbott, which allows booting floppy disk images inside RISC OS desktop. Thanks to his fantastic work you can play many classic games released for Acorn Archimedes on modern RISC OS machines, including Raspberry Pi.

The latest version available for Raspberry Pi at the moment is 2.50 beta, which can be downloaded from The Archimedes Software Preservation Project forum. Open !NetSurf, go to http://forums.jaspp.org.uk:9000/forum/viewtopic.php?f=9&t=228 and click on the post attachment (adffs250b.zip). A popup window "NetSurf Download" with a progress bar will appear. When download finishes click on the file icon (green square labeled "Data") and drag it to the SD card icon located on the iconbar. Double click the SD card icon to open the root folder of the card. You should see a green icon labelled "file" - it's the file you just downloaded. It's a zip archive containing !ADFFS, but the system does not recognize it, yet. Click with the middle mouse button on the file and select "File->Set type". The default value is "Data", change it to "Zip" and press Enter. The icon should turn blue with a big letter "Z" on it, which means that RISC OS now properly recognizes the file as a zip archive. Double click on it with the left mouse button to open the archive contents. You should see an icon labeled !ADFFS. Drag it to the folder you want to have it - I keep it in "Utilities" - and the installation is complete!

Now you need some games to play. I will use one of my favourite ones, Gods, as an example. First, download the full game archive from http://forums.jaspp.org.uk:9000/forum/viewtopic.php?f=25&t=107 just as you downloaded !ADFFS. Open the archive, go into Discs folder and drag the disc image files to a separate folder ($.Apps.Games.Gods for example). Again, you have to make the files recognized by the operating system by setting appropriate file type. Click middle mouse button on each file, select "File->Set type" and change "Data" to "Floppy". Observe the icons, they should change to !ADFFS-like.
When a game consists of only one floppy image, you can finish here.

With multi-disc games, you also need to change the image file names. It's because !ADFFS emulates a single drive and if you want to swap floppies their order is recognized by the suffix of the file name, so "Gods 1" becomes floppy number one, "Gods 2" becomes floppy number two, etc. To change the image name to conform to !ADFFS requirements click on the file with the middle mouse button, select "File->Rename", enter new file name and press Enter.

Finally, you can play the game! First, open the SD card, enter Utilities and run !SparkFS (if you opened any zip archive before it should already be running in the iconbar). !SparkFS comes preinstalled with RISC OS on Raspberry Pi, but if for some reason you don't have it, you can download a free read-only version (it's enough for !ADFFS) from RISC OS Open website.
Now run !ADFFS itself - it's icon appears on the iconbar. Drag "Gods 1" onto ADFFS icon on the iconbar to put the floppy image into the virtual disk drive. Click with the middle mouse button on the ADFFS icon on the iconbar and choose "Boot floppy". When asked about "Boot floppy via a simulated Shift-Break?" answear "Yes", and voila - the game starts. After playing the intro you will be asked to insert disc 2, which you can do by pressing CTRL-SHIFT-F2 (disc one is CTRL-SHIFT-F1, disc three is CTRL-SHIFT-F3, etc). To quit the game press CTRL-ESC.

Tip: Want to play once more? Just click on ADFFS, select "Boot floppy"... why the game won't start? Yes, you put disc 2 in the drive during the game! Drag "Gods 1" over ADFFS and try booting again. Enjoy!

Saturday, November 7, 2015

Using Raspberry Pi with a VGA monitor

One of the most fantastic Raspberry Pi features is its ability to fit in a pocket. Whether you travel far away from home or just go for a short visit you can always have your whole workplace with you. You don't have to copy all the files to a pendrive and then look for a computer to work on, wondering if you bring back home a virus or find your secret files "backed up" on some peer-to-peer network. You don't have to carry a big case with heavy latop inside, either. All you need is to take your Pi out of your pocket and connect a mouse, a keyboard, and a TV.
But what if there is only one TV set, and suddenly everybody wants to watch TV or play the latest hit on a game console? Yes, you can use a good old (S)VGA monitor! It can be an interesting alternative to a big TV. A flat LCD monitor takes little space on desk and can be a useful way to recycle some old electronic stuff, instead of just throwing it away. You can make the world a better place by reusing an old monitor with Raspberry Pi!
I will show you how to connect Raspberry Pi running RISC OS to a regular computer monitor with VGA input, but most of the tips below should be useful for Linux users as well.

Although Raspberry Pi does not feature a VGA output, there are many adapters available, which can convert digital HDMI data stream into analogue signal required by a VGA monitor. However, you have to pay attention to two very important things.
First, it has to be an adapter with a special DAC (Digital to Analogue Converter) chip. Some adapters just pass the signal through, and they can only work with PCs or laptops which can transfer an analogue signal through HDMI port. Raspberry Pi is not designed to support such feature.
Second, search for an adapter with audio output (the most popular is mini-jack port). It's because the Pi settings required to make it work with a VGA display can make the built-in mini-jack audio output port inactive. It is possible to have video signal passed through the adapter, and sound through a built-in audio jack, but it can be very tricky and the settings described below don't work for everybody. Moreover, if an adapter has an analogue audio output, it indicates that it has some kind of a DAC chip onboard, and is not a simple pass-through.
Hint: adapters advertised to work with a smartphone (or tablet) in most cases also work with the Pi. Anyway, before you buy such adapter, read it's description carefully or, if in doubt, ask the seller whether it was tested with Raspberry Pi. If you are still unsure, you can buy PiView, which is guaranteed to work with all Raspberry Pi models, but it costs almost as much as the Pi itself. Personally, I use an adapter I bought quite cheap on eBay and it works very well.

Now for the software part. The Pi can now speak to the monitor through the adapter, but the monitor will not send back the information the Pi expects to receive, so we need add some information to the Pi's default GPU (Graphics Processing Unit) configuration. This configuration is stored on a boot partition of the RISC OS SD card in a file called CONFIG.TXT. To edit this file on a PC, simply put the card into a reader and after it mounts open CONFIG.TXT from the mounted partition in the editor of your choice. To edit it from RISC OS, open !StrongED, click on the SD card icon on the iconbar, then hold down Shift and double click on !Boot icon, then Loader and drag CONFIG/TXT to !StrongED icon on the iconbar. The reason I recommend !StrongED over !Edit is that the former one can handle PC end-of-line codes better (!Edit displays [0d] at the end of each line).
The contents of the config file for RISC OS should look more or less like this:
fake_vsync_isr=1
framebuffer_swap=0
gpu_mem=64
init_emmc_clock=100000000
kernel=RISCOS.IMG
This is a basic configuration needed to boot RISC OS on Raspberry Pi. It will look a bit different for Raspbian and other Linux distributions, but it doesn't matter now. The parameters are written in "key=value" form, each in separate line. You can find a detailed description of the configuration parameters at Embedded Linux Wiki.
What you should do is to add the following lines to the configuration file. You can place them right after the last parameter, before the first one, or somewhere in the middle:
hdmi_force_hotplug=1
hdmi_group=2
hdmi_mode=17
Those lines require some explanation. The "hdmi_force_hotplug=1" tells the Pi to use to use HDMI output even if no connection with an HDMI with display was detected. As I mentioned before, a VGA monitor can't communicate with Raspberry Pi through HDMI, it can only display a picture received via the adapter. Next option "hdmi_group=2" selects DMT (Display Monitor Timig) output mode, which is a VESA (Video Electronics Standard Association) standard for VGA monitors, and "hdmi_mode=17" sets screen resolution to 1024x768 with 70Hz refresh rate. You should tweak that parameter depending on your monitor display capabilities, using information found at RPiconfig in DMT video modes table.

Now for the sound. If you have a VGA adapter with audio output and want to use it, you should add the following lines to your configuration:
hdmi_drive=2
hdmi_force_eid_audio=1
The "hdmi_drive=2" option selects HDMI mode with sound (value "1" means "no sound") and "hdmi_force_eid_audio" makes the Pi skip detection of the display's audio capabilities. Without this option you may get some strange sound problems, like no audio signal after first boot, suddenly reappearing after reboot.

If you want to use the Pi's built-in audio jack instead (you can't have both outputs active at the same time!), you should add these lines in place of the previous two:
hdmi_ignore_edid_audio=1
disable_audio_dither=1
The first option tells the Pi that there is no digital audio device connected and forces it to use the analogue output, and "disable_audio_dither=1" reduces some nasty noise you can sometimes get (if you have very quiet sound output you may try try to remove this parameter from the config file).

And that's it, enjoy your new Raspberry Pi display!