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Old 03-26-2011, 05:19 PM   #7
Iņigo
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Posts: 710
Karma: 72743
Join Date: Feb 2008
Location: Here or there
Device: iRex iLiad, in love with iRex DR800S. Also a K4NT. Now a Kobo Aura
Secret revealed

Executive summary
SysInfo is a proof of concept application written in a language called Vala [1] to test if Vala is a viable development method for iRex DR ereaders.


Historical note
During some months I've been maturing the idea to extend DR core programs without C, using an easier and faster (to write code in) language. So I started learning and playing with lua, waiting for LuaJIT [2] to be available for ARM processors. This would allow us to use the impressive FFI support in LuaJIT to call DR libraries from lua code without writing bindings. But ARM processors are not supported yet...

And I was musing this mood when I unexpectedly read a MobileReader thread I haven't seen before [3].
All credit for exploring this idea is for ross therefore.


Vala
Vala is a new language created in the GNOME desktop world. People say its syntaxis is similar to C# or Java, but I can't say it myself because I don't know much about both of them.

The main feature of Vala is that it compiles from .vala sources to C code, which is then compiled and linked to generate the final machine code. Note the whole compilation from .vala sources to binary program can be performed in just one step too.

Though more low level than lua or python, it's easier and faster to code than C, and offers much more faster execution speed than scripting languages (but not as fast as plain C).

Vala also comes with lot of "bindings" for many popular libraries.
And it's easy to write bindings for "our" DR libraries (take a look at "liberipc.vapi" file).

But the main advantage I see for DR development is that we could write modules in Vala easily, and then use these C sources to extend original firmware.


Current status of Vala for DR development
I've taken what ross provided and updated to support modern versions of Vala.
I've also fixed and improved the irex.vala and liberipc.vapi files. More will come as needed.

Note that Vala is not perfect, it's quite new and in continue development.
I've also found some issues: vala is so new that it sometimes depends on the last versions of glib to do some tasks, and this causes problems with the "old" libraries coming with DRs.
F.e, I couldn't find a better way to get current date and time in a custom format that to parse OS "date +fmt". Posix or glib 2.26+ contain functions to do it, but both of them are not available for DR development.

Anyway, I've been able to translate and improve a previously lua-written program (SysInfo) into vala without prior knowledgement of Vala or C# in ~10 hours of work. Most of this time was spent reading Vala documentation, fixing the Vala environment (irex.vala, liberipc.vapi) and fighting against some imcompatibilities between vala v0.11.x and DR older libraries.

I'm pretty satisfied with the results, this first program looks fast, robust, integrates well with DR and even doesn't depend on external runtime or libraries.

But what excited me most is the now opened possibility to write enhancements to core DR programs using a higher level language than C, so we could test new ideas faster and with less effort.


Instructions to compile SysInfo.vala
Steps:
Code:
- You need a running DR development environment
- Download, build and install Vala
  . download v0.11.7 from [1]
  . patch or change vala-0.11.7/vala/valaflowanalyzer.vala with the supplied file
  . build and install Vala using devel machine compiler (i.e, gcc, not arm-poky-linux-gnueabi-gcc)
- Build SysInfo:
  . put all the needed files in the same directory: SysInfo.vala, irex.vala, liberipc.vapi
  . set the cross-compiling environment:
    $ source /usr/local/poky/eabi-glibc/arm/environment-setup
  . run "make" or:
    $ valac --vapidir=. --pkg gtk+-2.0 --pkg=gdk-x11-2.0 --pkg liberipc --pkg posix SysInfo.vala irex.vala -o SysInfo
- That's it
  . there will be many warnings, they don't matter
Installation
This is a vala testing package not intented for general use.
Anyway, you can copy the "bin" folder contents to <SD card>/Programs to get a fully functional program.
Eventually I'll split these contents into a SysInfo package for end user consumption and a vala development package.


[1] http://live.gnome.org/Vala
[2] http://luajit.org/
[3] http://www.mobileread.com/forums/showthread.php?t=39212


Kind regards,
Iņigo Serna
Attached Files
File Type: gz Vala-SysInfo.tar.gz (51.4 KB, 92 views)
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