devcon

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+#define _PAGE_ Rockbox Developer Conference 2002
+#include "head.t"
+
+<table align="right"><tr><td><a href="show.cgi?img4083.jpg"><img src="img4083t.jpg" alt="photo" border=0 width=200 height=150></a><br><small><i>Comparison of Recorder and Player</i></small></td></tr></table>
+
+<p>Well, almost. :-) Björn, Linus, Daniel and Kjell sat down at Linus' house
+friday night (2002-04-19) with our Archoses and had a long and fruitful discussion about software design.
+Here are a few things that we discussed:
+
+<h2>Application Programming Interfaces</h2>
+
+<p>We want to try to stick to POSIX where these exist and are practical. The
+reason is simply that many people already know these APIs well. Here are a
+few which haven't already been defined in the code:
+
+<h3>File operations</h3>
+<ul>
+<li>open
+<li>close
+<li>read
+<li>write
+<li>seek
+<li>unlink
+<li>rename
+</ul>
+
+<table align="right"><tr><td><a href="show.cgi?img4084.jpg"><img src="img4084t.jpg" alt="photo" border=0 width=200 height=150></a>
+<br><small><i>Contest: Spot the development box!</i></small></td></tr></table>
+
+<h3>Directory operations</h3>
+<ul>
+<li>opendir
+<li>closedir
+<li>readdir
+</ul>
+
+<h3>Disk operations</h3>
+<ul>
+<li>readblock
+<li>writeblock
+<li>spindown
+<li>diskinfo
+<li>partitioninfo
+</ul>
+
+<p>We also decided that we will use the 'newlib' standard C library,
+replacing some functions with smaller variants as we move forward.
+
+<h2>Multitasking</h2>
+
+<p>We spent much time discussing and debating task scheduling, or the lack
+thereof. First, we went with the idea that we don't really need "real"
+scheduling. Instead, a simple "tree-task" system would be used: A
+main-loop, a timer tick and a "bottom half" low-priority interrupt, each
+with an event queue.
+
+<p>Pretty soon we realized that we will want to:
+
+<ol style="a">
+<li> Use a timer tick to poll disk I/O (assuming we can't get an interrupt)
+<li> Perform slow disk operations in both the MP3->DAC feeder and the user
+     interface, sometimes at the same time.
+<li> Not lock up the user interface during I/O.
+</ol>
+
+<table align="right"><tr><td><a href="show.cgi?img4086.jpg"><img src="img4086t.jpg" alt="photo" border=0 width=200 height=150></a>
+<br><small><i>A stack of "virgins"!</i></small></td></tr></table>
+
+<p>At the same time, we agreed that we should not walk into the common trap
+of engaging in "job splitting". That is, to split up jobs in small chunks
+so they don't take so long to finish. The problem with job splitting is
+that it makes the code flow very complex.
+
+<p>After much scratching our collective heads over how to make a primitive
+"three-task" system be able to do everything we wanted without resorting
+to complex job splitting, we finally came to the conclusion that we were
+heading down the wrong road:
+
+<p><blockquote>
+ <b>We need threading.</b>
+</blockquote>
+
+<p>Even though a scheduler adds complexity, it makes the rest of the code so
+much more straight-forward that the total net result is less overall
+complexity.
+
+<p>To keep it simple, we decided to use a cooperative scheduler. That is, one
+in which the threads themselves decide when scheduling is performed. The
+big gain from this, apart from making the scheduler itself less complex,
+is that we don't have to worry as much about making all code "multithread
+safe".
+
+<p>Affording ourselves the luxury of threads, we soon identified four basic
+threads:
+
+<ul>
+<li>Disk thread, performing all disk operations
+<li>UI thread, handling the user interface
+<li>MP3 feed thread, making sure the MAS is fed with data at all times
+<li>I2C thread, handling the sometimes very relaxed timing of the I2C bus
+</ul>
+
+<p>Threads use message passing between them and each have a message queue
+associated to it.
+
+<table align="right"><tr><td><a href="show.cgi?img4089.jpg"><img src="img4089t.jpg" alt="photo" border=0 width=200 height=150></a>
+<br><small><i>There's much fun to be had with these things!</i></small></td></tr></table>
+
+<p>In addition to the threads, we need a timer interrupt with the ability to
+send messages to threads at specific intervals. This will also be used to
+scan the keys of the jukebox and handle key repeat detection (when a key
+has been pressed for a number of ticks).
+
+<p>None of these things are, of course, written in stone. Feel free to
+comment, discuss and argue about them!
+
+<p>We are currently 89 subscribers to this list. If you want to get more
+deeply involved in what's going on, I encourage you to:
+
+<ul>
+<li>Subscribe to the rockbox-cvs list, to see all code that goes in.
+<li>Join the #rockbox channel on irc.openprojects.net. There are always a
+couple of us in there.
+</ul>
+
+<p>I have written a set of guidelines for contributing code to the project.
+Take a look at them in CVS or here:
+<a href="http://bjorn.haxx.se/rockbox/firmware/CONTRIBUTING">CONTRIBUTING</a>
+
+<p>/Björn
+
+#include "foot.t"