You can save bandwidth by pre-compressing your JavaScript files with gzip without relying on dynamic compression such as mod_deflate.  To to this properly and having it working across all browsers you’ll need to modify your webserver to return the correct mime type and encoding for the file.

Most browsers are quite liberal in what they accept, except for Safari/Konqueror. For some reason it doesn’t like it if a JavaScript file ends in .gz, it ignores the content-encoding and attempts to read the compressed data as JavaScript. The key to make it work is to create a new extension, for example .jgz and set the Content-Encoding for this extension to gzip AND to set the mime type of .js to text/javascript, not text/plain or application/x-javascript.

To recap, call the file script.js.jgz and make sure your webserver delivers it with the following options

Content-Encoding: gzip
Content-Type: text/javascript

Just include the file as usual

<script type="text/javascript" src="script.js.jgz"></script>

This has been tested with the following browsers

• Firefox 3.0/3.5
• Opera 10
• Internet Explorer 7
• Konqueror (webkit based, behaves like Safari)
• Google Chrome 3
• Epiphany

Apache

Put the following in a .htaccess file

AddType text/javascript .js
AddEncoding gzip .jsz

thttpd

Add jsz gzip to mime_encodings.txt and change the type for js in mime_types.txt to js text/javascript.

VirtualBox (host mode) was quite recently ported to FreeBSD, some bits are still missing particular network support. So I spent the last couple of days hacking on it and how have a working implementation that supports bridged adapters.

Update 10 Sep: The patches have been committed upstreams.
Update 9 Sep: working vboxnetadp and patchset sent upstreams.
Update: Re-written to use netgraph, now works on FreeBSD 7 and 8

Patches can be found at

http://www.shapeshifter.se/pub/patches/virtualbox/vbox-freebsd-netif-20090908.patch
http://www.shapeshifter.se/pub/patches/virtualbox/vbox-freebsd-vboxnetadp-20090908.patch
http://www.shapeshifter.se/pub/patches/virtualbox/vbox-freebsd-vboxnetflt-20090908.patch
http://www.shapeshifter.se/pub/patches/virtualbox/Config.kmk-20090908.patch
http://www.shapeshifter.se/pub/patches/virtualbox/src-VBox-HostDrivers-Makefile.kmk-20090908.patch

Additional patches to test with the 3.0.51.r22226 version in FreeBSD ports.

http://www.shapeshifter.se/pub/patches/virtualbox/Config.kmk-r22226-20090908.patch
http://www.shapeshifter.se/pub/patches/virtualbox/virtualbox-port-20090907.patch
http://www.shapeshifter.se/pub/patches/virtualbox/ConsoleImpl2.cpp.patch

Re-install VirtualBox through ports using the following commands

Apply/compile with
cd /usr/ports/emulators/virtualbox
make clean patch
mkdir work/virtualbox-3.0.51r22226/src/VBox/HostDrivers/VBoxNetFlt/freebsd
mkdir work/virtualbox-3.0.51r22226/src/VBox/HostDrivers/VBoxNetAdp/freebsd
patch < virtualbox-port-20090907.patch
patch -d work/virtualbox-3.0.51r22226/Config.kmk-r22226-20090908.patch
patch -d work/virtualbox-3.0.51r22226/ConsoleImpl2.cpp.patch
patch -d work/virtualbox-3.0.51r22226/src-VBox-HostDrivers-Makefile.kmk-20090908.patch
patch -d work/virtualbox-3.0.51r22226/vbox-freebsd-netif-20090908.patch
patch -d work/virtualbox-3.0.51r22226/vbox-freebsd-vboxnetadp-20090908.patch
patch -d work/virtualbox-3.0.51r22226/vbox-freebsd-vboxnetflt-20090908.patch
make install

In VirtualBox network settings, under "Bridged Adapter" you should now see your available network interfaces. Select the one connected to your network and boot your virtual machine. It should now be connected to your local network as any other machine.

Host only adapter mode can be used to create a virtual network with multiple guests, it creates a special vboxnetX adapter on the host. You'll have to do normal routing between this interface to get outside connectivity.

In addition to vboxdrv.ko you'll have to load vboxnetflt.ko and vboxnetadp.ko too.

kldload /boot/modules/vboxnetflt.ko
kldload /boot/modules/vboxnetadp.ko

A project I’ve been hacking on for a while is a self-contained 1-wire to IPv6 bridge based on an Atmel AVR ATmega644 and the ENC28J60 Ethernet controller from Microchip.

1-wire: is a serial bus from Dallas Semiconductor/Maxim that only requires 1 data line, there are a number of cheap sensors and other devices for this bus. The strength of this bus is not its speed but that it supports large ranges (up to 300 meters).
Also, each 1-wire device has a permanent unique 64-bit serial number.

IPv6: Insanely large address space. It’s common to use a 64-bit netmask for site networks so that EUI-64 based addresses can be used for auto configuration. This leaves 64-bit for the node address – do you see where this is going now…

Yes..I’ve built a device that assigned each 1-wire device it’s connected to its own IPv6 address. Why? you ask, mostly because I can.

Hardware

As mentioned above, the device is based on an AVR ATmega644. It has 64KB of flash memory for program code and 4KB of RAM. It’s running on its built-in oscillator at 8MHz. The ENC28J60 Ethernet chip is connected to the AVR using SPI. The rest of the hardware is mostly for power distribution and management.

The PCB was manufactured by BatchPCB, cheap service but a bit slow turn-around time.

Unfortunately I screwed up the SPI connection but I managed to fix that with some green wires (or black wires in this case). You’ll note them in the picture above.
I also intended to run the AVR at 5V and the ethernet chip at 3.3V. This is what the quad AND-gate in the upper right
corner was for, but since I screwed up the SPI routing it’s disconnected and the whole circuit is running at 3.3V.
The ENC28J60 can only run at 3.3V, the AVR has a range from 2.8-5V and 1-wire should be ran at 5V but works at 3.3V. Hence the need for TTL voltage translation.

As for the 1-wire devices I had implemented a bus master in software that generated the require waveforms. It worked great up to about 10-15 meters. Any cable length greater than that refused to work.
This was a bit unexpected and without an oscilloscope it was more or less impossible to figure out where and how the signals got mangled. So I simply got a DS2480 1-wire line driver that generates the required signals in hardware with more precise timing.

Add-on board with a 1-wire master

This required an add-on board and because I didn’t want to wait for a new PCB I used a 2.54mm prototype board. With the DS2480 only available in SOIC8 packages it required some “creative” soldering .
The DS2480 required 5V, thus It had to get its own power supply and also required level translation on the UART line between this device and the AVR. I choose an approach using MOSFETs and a few resistors for this (the TO92 packages in the picture above). This turned out to work really good and I think I’m going to use this for the SPI level translation in the next revision of the board.
The wire leaving the board on the left side leads to the 1-wire sensor devices.

The add-on board is extremely ugly. But hey, it works.

Future improvements for the next revision

• Use of external crystal at 16MHz instead of internal 8MHz clock.
• Use MOSFETs for 3.3-5 V translation. Need to test it at 16MHz before manufacturing a PCB though.
• Obviously fix all PCB errors
• All SMD parts (resistors and voltage regulators) to shrink PCB size even more.
• Better power distribution. I was a bit too conservative with the decoupling capacitors resulting in some weird power problems (fixable with some caps)
• Create a real add-on board

I’ll publish the PCB CAD files when the next revision is complete.

Software

The only small IPv6 stack I know of is the uIPv6 stack in the Contiki operating system created by Adam Dunkel et al. This is unfortunately only available together with Contiki and not as a stand alone package as the originally uIP (IPv4) stack.

Contiki is a great operating system, but when you only have 4KB of RAM it becomes a bit heavy weight. So I broke out the uIPv6 stack from Contiki and made it run stand alone and ported in to AVR. I also ported the web server application from Contiki and made it run on AVR. As I wanted to use multiple IPv6 addresses I also had to add support for IP aliases to the uIPv6 stack.

Since the uIPv6 was integrated with Contiki it used the Contiki process model which it self is based on “proto-threads” (another thing invented by Adam Dunkel). I felt that this didn’t fit so I turned all processes into a polling mode instead. So one has to call a set of polling functions from the main application loop or from timers.

The other major parts of the code are drivers for ENC28J60, DS2480 and DS1820.

Software

1-wire devices

30 second polling interval with auto-discovery of new devices.
Each device is assigned its own IPv6 address, requires a /64 network to be available.

Webserver

Integrated web server makes it possible to visit each address. An XML file with the latest sensor reading is returned. An “age timestamp” is also provided which makes it possible to determine how old the reading is.

Currently, with 5 1-wire devices connected it uses about 3KB of RAM.

• Source code
• uIPv6 port

In-action

I only have temperature sensors connected at the moment. If you happen to have an IPv6 capable connection you can access the sensors through a web browser.

2001:16d8:ffe5:002:2894:eaf6:100:0c7
2001:16d8:ffe5:002:28c1:b4f6:100:035
2001:16d8:ffe5:002:2809:aef6:100:0ca
2001:16d8:ffe5:002:28c5:a5f6:100:058
2001:16d8:ffe5:002:2813:caf6:100:050

(If you don’t have IPv6 you should get it, or you can view graphs based on the sensor values at lindberg.tl instead).

Do you have a bunch of useless USB-to-PS/2 keyboard adapters laying around? Two of them make a great female-female USB adapter – If you need one that is. Here is how I made one.

Carefully crack the case open using a knife. You can be quite rough at the PS/2 end of the casing as this part will be
removed anyway. Don’t destroy the USB side of the casing as this part will be reused for our adapter casing later on.

Once opened you should basically have a USB-connector connected to a PS/2 connector covered in hot glue/plastic wrapped in a thin-foil like material (for shielding). Remove the wrapping and cut away the PS/2 connector with a knife.

Now, carefully remove the remaining plastic. Don’t worry about the soldered wires but make sure that you don’t damage the pins on the USB connector. You should end up with something like this.

Do the same with another USB-PS/2 adapter so that you basically end up with two USB connectors.
Bring out your soldering iron and de-solder the remaining wires from the connectors.

Place the connectors back-to-back and turn one of them 180 degrees so that it becomes “up-side-down”. If you don’t do this you’ll end up connecting the pins in the wrong way.
To make the pins touch each other you’ll have to bend them roughly 30-45 degrees. Solder the pins together.

Cut out a piece of wire and solder it to the casing off each connector. You can use the existing solder points used for the shielding/ground or create a new. Some flux will help a lot here.

That’s it for the connector. Next up is to creating a new casing using the existing casings. Unfortunately I forgot to take pictures of this process.
Take on pair of the two cases, take one of the two pieces and place the USB-USB adapter inside it . Make a mark on the casing approximately in the middle of where the soldered pins meet.
Cut at this point and do the same for the same half of the other case. Just do a rough cut and file the pieces until the adapter fits. Once the bottom fits, do the same for the top part using the bottom pieces as a template.

Place it in the new casing and pour some hot glue over it to make it steady. Glue the top on and it’s complete.

USB-USB female adapter in action.

Will it be as good as a commercial adapter? probably not. Will it effect data transmission? probably (depending on how good the solder joints are). Cheaper than a commercial adapter? yep (assuming you already have the parts needed and don’t factor in the labor )

Handy system clock for AVR 8-bit microcontrollers suitable for measuring elapsed time or for use with timers. This provides
a monotonic time since system startup (like the POSIX CLOCK_MONOTONIC).

The system clock is based around a 32kHz clock crystal and one of the 8-bit timers provided by the AVR, it is possible to use the CPU frequency as a timer base as long as it’s a nice, dividable, frequency.
To be able to provide a stable 1 Hz clock but still have sub-second precision we divide 1 second into an arbitrary number of
system ticks. To minimize CPU usage the tick counter should be increased at each interrupt, this means that the number of
ticks per second we we choose determines our interrupt frequency and timer resolution.
How to choose number of ticks? It all depends on your required resolution, if you only want a 1 second resolution a tick and a second becomes equal.

The AVR timer is a 8-bit register that simply counts at the rate of its clock source. The clock source can be either the CPU
clock or an external oscillator, the clock source is also subject to a prescaler to further decrease the frequency.
The timer then generates an interrupt on overflow and/or when it hits a pre-configured value.
Since its a 8-bit timer, we have a maximum of 256 cycles before an interrupt is generated, a smaller interval can be achieved by using the comparator match to generate an interrupt at a specific value.

This example is creating a 1/32 second resolution timer (32 ticks per second) using an external 32768 Hz watch crystal.
comp is the comparator value, to avoid re-arming it with different values it should be limited to 128 or 256, otherwise it has to be changed at each interrupt.

The following to equations can be used to calculate either comp or the prescale value.
prescale is limited by the target device, but common values are powers of 2 (8,32,64,128,256,1024).

Using 128 as the comp value and inserting the other values into equation 2 yields the following prescaler

So, a prescaler of 8 gives us two interrupts per 256 cycles, one at 128 and one at 256 (overflow). Using 256 as comp would yield a perscaler of 4 but the target device I used didn’t have a TS/4 prescaler.

Complete source code for a 1/32 (or 31.25ms) second resolution timer for the ATmegaxx4 using Timer 2 and a 32kHz watch crystal connected to the pins TOSC1 and TOSC2.
Requires AVR libc.

#include <avr/io.h>
#include <avr/interrupt.h>
 
typedef uint32_t clock_time_t;
static clock_time_t global_system_ticks = 0;
 
/* ISR for the timer overflow */
ISR(TIMER2_OVF_vect)
{
    global_system_ticks++;
}
 
/* ISR for the comparator */
ISR(TIMER2_COMPA_vect)
{
    global_system_ticks++;
}
 
/* Return number of elapsed ticks */
clock_time_t clock_time()
{
    return (global_system_ticks);
}
 
/* Return number of elapsed seconds */
unsigned long clock_seconds(void)
{
    uint32_t tmp;
 
    TIMSK2 &= ~(1 << OCIE2A) | (1 << TOIE2);
    tmp = global_system_ticks / 32;
    TIMSK2 |= (1 << OCIE2A) | (1 << TOIE2);
    return (tmp);
}
 
void clock_init()
{
 
    /* Enable external oscillator (32 kHz crystal) connected to TOSC{1,2} */
    ASSR |= (1 << AS2);
 
    /* Reset timer */
    TCNT2 = 0;
 
    /* Set TS/8 prescaler, results in a 4096Hz clock */
    TCCR2B |= (1 << CS21);
 
    /* Compare at half counter value */
    OCR2A = 128;
 
    /*
     * Enable overflow and compare interrupt.
     * Triggers each 1/32 secs
     */
    TIMSK2 |= (1 << OCIE2A) | (1 << TOIE2);
}