15 Jan 10 Embedded Linux Programmer

As an embedded linux programmer, I’ve had the opportunity to work on a number of different platforms, MIPS being one of my favorites.

There are a few general limitations that you’ll find. You have limited CPU power available, you have very little RAM available, and for more advanced operations and optimizations, your CPU will generally have a limited function set.

The usual good programming practices apply, but are of much greater importance. Specifically, don’t allocate memory that you don’t need, and dont put the CPU under undue stress with unnecessary or badly optimized loops. Taking C syntax and some pseudo code;
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Tags: assembler, embedded, loop, mips, optimize, x86

15 Nov 09 PHP Developer – Loops in General

There are 3 types of loop in PHP:

while (condition)
{ code_goes_here; }

do
{ code_goes_here; }
while (condition);

for(expr1, expr2, expr3)
{ code_goes_here; }

In terms of the ‘for’ loop above, ‘expr1′ being the starting expression, i.e. $i=0. expr2 being the condition that must be satisfied to keep the loop running, i.e. $i < 100. expr3 being the expression evaluated each time the loop runs, i.e. $i++. Each loop type has it’s uses.
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Tags: do, for, loop, MySQL, PHP, PHP Developer, PHP MySQL Developer

05 Nov 09 PHP Developer – Looping through database results

As a PHP Programmer, a very routine PHP/MySQL procedure is fetching a set of records from the result of a query.

$sql = "SELECT ...";
$result_set = mysql_query($sql);
for ($ctr = 0; $ctr < mysql_numrows($result_set); $ctr++)
{
    $my_object = mysql_fetch_object($result_set);
    //do something with $my_object
}

Now as tidy as the above code is, what’s the big problem? The number of rows returned by the query remains the same throughout. Why are we calling the mysql_numrows function on the same result set, to return the same answer over and over, possibly thousands of millions of times depending on the size of the result set? On a larger web application with a larger result set, things like this will dramatically increase unnecessary overhead. This is one of the most basic optimizations to make:

$sql = "SELECT ...";
$result_set = mysql_query($sql);
$result_num = mysql_numrows($result_set);
for ($ctr = 0; $ctr < $result_num; $ctr++)
{
    $my_object = mysql_fetch_object($result_set);
    //do something with $my_object
}

Now, there’s a couple of different methods you can use to achieve the same purpose, some of which may actually be more appropriate, such as a simple while loop, but the purpose of this article was to illustrate the issue above solely. More on optimization later..

Tags: for, loop, MySQL, PHP, php programmer, sql

08 Mar 09 How to create a simple disk image formatted to ext3

We want a 48MB image, formatted to ext3

ns3:/tmp# dd if=/dev/zero of=./disk.img bs=1MiB count=48
48+0 records in
48+0 records out
50331648 bytes (50 MB) copied, 0.301372 s, 167 MB/s
ns3:/tmp# mkfs.ext3 ./disk.img
mke2fs 1.41.3 (12-Oct-2008)
./disk.img is not a block special device.
Proceed anyway? (y,n) y

ns3:/tmp# mkdir disk

ns3:/tmp# mount -oloop ./disk.img ./disk
ns3:/tmp# df -h ./disk
Filesystem            Size  Used Avail Use% Mounted on
/tmp/disk.img          47M  4.8M   40M  11% /tmp/disk

That’s it – now we can copy our content to ./disk before unmounting it, then use dd to write it to our target medium (such as a CF card or similar)

ns3:/tmp# umount ./disk

Tags: CF, df, disk image, ext3, loop, mkfs.ext3, mount, umount