No Znx!

I was further discussing C ideas and this time we came across bit flags (also called bit fields). The idea behind them is conservation of memory, a boolean data type consumes 1 byte of memory but all that is really needed is a single bit. Therefore you can store several booleans in a single byte.

Here is a simple example, note that each has a specific value to ensure that each matches a single bit in the 8-bit variable:

enum options {
  option_a = 0x01,  /*   1 == 00000001 */
  option_b = 0x02,  /*   2 == 00000010 */
  option_c = 0x04,  /*   4 == 00000100 */
  option_d = 0x08,  /*   8 == 00001000 */
  option_e = 0x10,  /*  16 == 00010000 */
  option_f = 0x20,  /*  32 == 00100000 */
  option_g = 0x40,  /*  64 == 01000000 */
  option_h = 0x80,  /* 128 == 10000000 */
};

So basically we have 8 boolean flags (0 off/false, 1 on/true). We can use these by utilising bitwise operations. There is really only 3 operations that you will use regularly on bit flags so lets see them.

Switching individual/multiple options “on” (or setting value true):

options |= option_a;
/* Translates to:
  options = options | option_a;
  options = 00000000 | 00000001;
  options = 00000001;
*/
 
options = option_a | option_c | option_h;
/* Translates to:
  options = 00000001 | 00000100 | 10000000;
  options = 10000101;
*/

Equally switching options “off” (or setting false) can be done as follows (note we are using the options from above, thus a, c and h are on):

options &= ~option_a;
/* Translates to:
  options = options & ~option_a;
  options = 10000101 & ~00000001;
  options = 10000101 & 11111110;
  options = 10000100;
*/

Obviously you need a basic grasp of boolean mathematics to be able to handle this but learning the basics shouldn’t be too hard. Finally the last thing to do is check to see if a flag is “on” or “off” (again using the options from before, so c and h are “on”:

if( options & option_b ) printf("B is ON\n");
/* 10000100 & 00000010 = 00000000 .. i.e. false, so no output */
if( options & option_c ) printf("C is ON\n");
/* 10000100 & 00000100 = 00000100 .. i.e. true, so "C is ON" is outputting */

As with most things in C, once you start using and abusing it should start to fall into place. I hope that this serves as a basic introduction to bit fields.

With C++ there is ways of handling optional function parameters or overloading functions to handle different amounts of parameters, obviously within C these abilities do not exist. However if we wanted to handle a variable list of parameters then C and C++ would work the same.

Let’s see how we’d do that:

#include <stdarg.h>
#include <stdio.h>
 
int Adding(int cnt, ...) {  /* the three ... indicate a variable list */
    int add, tmp, i;
    va_list args;            /* make a va_list */
    va_start(args, cnt);     /* variable list starts after 'cnt' */
    for(i = 0; i < cnt; i++) {
        tmp = va_arg(args, int); /* grab the next */
        add = add + tmp;         /* add to the sum */
    }
    va_end(args);    /* finished using variable list */
    return add;
}
 
int main( ) {
    int a;
    a = Adding(2, 1, 2);
    printf("%u\n", a);     /* Outputs 3 */
    a = Adding(3, 1, 2, 3);
    printf("%u\n", a);     /* Outputs 6 */
    return 0;
}

So the first argument indicates how many variables we are going to pass and the rest are summed together. The function Adding() would be identical in C++.

Sometimes when people are using Linux they will find that they come across a simple security check that confirms the authenticity of the RPM/Deb files that they are installing. Every so often the key is missing but that is easy to remedy. Here I will use an example with the YUM install of Adobe Flash:

[root@marine]# ls
adobe-release-i386-1.0-1.noarch.rpm
[root@marine]# yum localinstall adobe-release-i386-1.0-1.noarch.rpm
Loaded plugins: fastestmirror, priorities
Setting up Local Package Process
Examining adobe-release-i386-1.0-1.noarch.rpm: adobe-release-i386-1.0-1.noarch
Marking adobe-release-i386-1.0-1.noarch.rpm to be installed
Loading mirror speeds from cached hostfile
* addons: anorien.csc.warwick.ac.uk
* base: anorien.csc.warwick.ac.uk
* centosplus: anorien.csc.warwick.ac.uk
* contrib: anorien.csc.warwick.ac.uk
* extras: anorien.csc.warwick.ac.uk
* rpmforge: fr2.rpmfind.net
* updates: anorien.csc.warwick.ac.uk
588 packages excluded due to repository priority protections
Resolving Dependencies
--> Running transaction check
---> Package adobe-release-i386.noarch 0:1.0-1 set to be updated
--> Finished Dependency Resolution

Dependencies Resolved

================================================================================
Package              Arch     Version Repository                          Size
================================================================================
Installing:
adobe-release-i386   noarch   1.0-1   /adobe-release-i386-1.0-1.noarch   1.9 k

Transaction Summary
================================================================================
Install      1 Package(s)
Update       0 Package(s)
Remove       0 Package(s)

Total size: 1.9 k
Is this ok [y/N]: y
Downloading Packages:
warning: rpmts_HdrFromFdno: Header V3 DSA signature: NOKEY, key ID f6777c67

Public key for adobe-release-i386-1.0-1.noarch.rpm is not installed

As you can see it attempted to install but because the key was missing it refused to install. So what do we do to find that key? First we must download the key from somewhere, there is various key servers around the world, some of the most popular are (note hkp is the HTTP keyserver protocol):

• hkp://subkeys.pgp.net
• hkp://pgp.mit.edu
• hkp://keys.gnupg.net
• hkp://wwwkeys.uk.pgp.net (where UK can be replaced by any country code)

So lets search for the missing key:

[root@marine]# gpg --keyserver hkp://wwwkeys.uk.pgp.net --recv-keys f6777c67
gpg: requesting key F6777C67 from hkp server wwwkeys.uk.pgp.net
gpg: /root/.gnupg/trustdb.gpg: trustdb created
gpg: key F6777C67: public key "Adobe Systems Incorporated (Linux RPM
  Signing Key) " imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg:               imported: 1

So now we have the key and see that it is indeed Adobe’s key. Now all we need to do is add into RPM:

[root@marine]# gpg --armor --export f6777c67 >tmp-gpg.key
[root@marine]# rpm --import tmp-gpg.key

Simple as that, the install will work now!

This post is a refreshed look at a previous post on the same matter.

A couple of days ago I opened up my AAO and discovered that it was out of charge. I plugged it in and started using it, then I spotted that the power indicator said the battery was full. I knew that couldn’t be right as it was only 5 minutes since I plugged it in.

I stopped what I was doing and shutdown, then I removed the power and attempted to turn on again. Once more the machine wouldn’t turn on but I noted that the charging light wasn’t showing either.

A quick google and I discovered that I was not alone with this issue. It seems two types of AAO (the AOA100 and AOA150) can suffer from this problem. There is a fix and a workaround, the fix is obviously the better option. The workaround is to unplugged the battery from the device then power it up. After a moment, plug the battery back in and it should start charging, not ideal.

The fix is to download a BIOS update and patch it! Obviously you must insure that your AAO is the correct model before you attempt to flash the BIOS otherwise you might leave yourself with a very pretty brick. To ensure this you should find a label on the bottom of you device saying AOA150 or AOA100. Although my model indicated ZG5, a quick check on another label and I spotted AOA150.

The instructions on how to do this are available from Acer’s Support website. I will reproduce here what I did:

1. Turn on the netbook and enter the BIOS by pressing the button F2
2. Take note of the version number, this should change if the upgrade is successful.
3. Open a browser and go to the Acer website.
4. Browse through: Service & Support > Driver Download > Netbook > Aspire One > AOA150 (or 100) > BIOS
5. Donwload the file, it will be a zip.
6. Extract the zip and rename the file 3310.fd to be zg5ia32.fd.
7. Plug in a USB stick, and copy two files over, the zg5ia32.fd and FLASHIT.EXE
8. Make sure you have your netbook plugged in and powered on.
9. Power down the netbook
10. Press and hold down the Fn and Esc keys and then press the power button
11. When the power light comes on, wait a couple of seconds and then let go of the buttons
12. It will look like very little is happening, the screen stays blank, but you should see your USB light blinking.
13. After a while (it took around 2 minutes for me) the netbook will reboot itself and power on.

After this I powered up the device and spotted that the same thing was occurring. I rebooted and did the same process again. This time I entered the BIOS and spotted that the version number had changed.

So once it was back up, I waited a few minutes and spotted that the power indicator said it was charging the battery, success! Whilst I would normally not advise this sort of process for the average user, Acer had made it relatively simple and I feel some what foolproof.

Obviously if it doesn’t work for you then the next step would be to try the workaround or maybe go ahead and contact Acer if your warranty is still valid.

Oh and Happy Christmas to all !

Just came across a really good site with lots of tips and tricks for the AA1.

I have owned this dinky wee notebook for sometime now and can highly advise it for anyone looking for a Linux Notebook.

Some tricks I have are:

Alt+F2 > xfce-settings-show > Desktop > Behaviour > Show desktop menu on right click.
The will enable the XFCE menu on right click, which is useful to me.

Alt+F2 > xfce-settings-show > Sessions and Startup > Advanced > Launch Gnome services on startup
This will allow NetworkManger to use gnome-keyring and therefore finally store the keys for wireless!

Simple but effective!