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Tuesday, October 27th, 2009

Transcend 1 – Kingston 0

Translation: [ Google | Babelfish ]

Categories: [ IT ]

J'ai acheté il y a un an et demin un lecteur de cartes mémoires SD Kingston MobileLite. Il fonctionnait correctement sur ma vieille Debian Etch (avec un noyau 2.6.18), mais après l'avoir mise à jour en Lenny (noyau 2.6.26), le lecteur à cessé de fonctionner. Je l'ai renvoyé en garantie, on me l'a échangé contre un neuf, qui ne fonctionne pas mieux. Après un certain temps passer à fouiner sur le web, j'ai appris que quelque part entre le 2.6.18 et le 2.6.26 un certain nombre de contournements de bugs on été ajoutés au noyau afin de faire fonctionner des lecteurs de cartes SD plus ou moins mal foutus. Le résultat, c'est que le Kingston, qui est lui aussi mal foutu, mais différemment, ne fonctionne plus. La raison profonde, c'est que Linux tente de lire le dernier secteur de la carte (pour en déterminer la taille ?) et que lors d'une lecture par blocs, si le bloc contient le dernier secteur, le firmware du lecteur plante. Et s'il contient l'avant dernier secteur, il plante aussi. Le noyau 2.6.30 souffre également de ce bug, donc le problème n'a pas été corrigé depuis le 2.6.26. Et comme le lecteur ne fonctionne qu'une fois sur deux avec Leffakone (noyau 2.4.22), j'ai donc décidé de changer de crèmerie : j'ai acheté un lecteur Transcend P5, au nom nettement moins marketing, mais qui au moins fonctionne du premier coup. Transcend roulaize (pour le moment), Kingston pas.

[ Posted on October 27th, 2009 at 20:55 | 2 comments | ]

Tuesday, October 20th, 2009

Reverse Engineering the param.cfg file of Cowon's iAudio 7 player

Categories: [ IT ]

While I'm eating at work, I like to listen to the same podcast I was listening while commuting. But I don't want to search manually which file I was listening to, and at what point in the podcast I shut the player down. Since this information is probably in the player's system files somewhere, I just had to hack a bit and see if I could extract it.

The relevant file is system/param.cfg. At offset 0x0F, one can read a big-endian 16-bit number which is the offset in seconds from the beginning of the file where playing was stopped. That part was easy.

Now for the actual file. At offset 0x879, one can read a big-endian 32-bit number which is the first File Allocation Table entry of the file. And somehow, this wasn't difficult to guess, I probably would have designed it that way myself… Thankfully, the Mtools package in GNU offers a tool called mshowfat which takes a DOS path as an argument and returns the FAT range occupied by that file.

And Bob's your uncle.

[ Posted on October 20th, 2009 at 12:23 | no comment | ]

Monday, October 19th, 2009

Sauna Physics

Categories: [ Science ]

We discussed sauna physics during this morning's coffee break, especially whether one should throw cold or hot water on the stones.

Here are the physical values:

In other words, you need 355 J to heat 1 g of water from a cold 15 °C to 100 °C, and another 2,260 J to evaporate it; the heating part represents only 14% of the total required energy. If you use hot water (60 °C), you need 167 J plus 2,260 J; the heating here represents 7% of the energy. The relative difference in required energy between cold water and hot water is less than 8%; accoring to my former chemistry teacher, if it's less than 10%, it's negligible.

Additionally, if we consider that 1 kg of burning wood produces roughly 10 MJ (from Wikipedia's Wood fuel article; it depends very much on its moisture content and the efficiency of the furnace, but in ideal conditions you can get 16 MJ out of it), we need about 25 g of wood to evaporate 0.1 L of cold water. Given that I put about 5 kg of wood into the furnace and throw well below a litre of water to the stones, the temperature of the water won't really matter.

The sudden cooling down of the surface of the stones from 300-350 °C to 100 °C when pouring water on them may however have an impact on their capacity to absorb and regulate the heat.

[ Posted on October 19th, 2009 at 17:30 | no comment | ]

Saturday, October 3rd, 2009

Sähkönkulutus 2

Translation: [ Google ]

Categories: [ Science ]

Mitattiin uuden, A-luokkaisen pesukoneen sähkönkulutus:

  • Säästöohjelma, 40 °C: 150 min, 0.79 kWh, max 2.3 kW

[ Posted on October 3rd, 2009 at 18:53 | no comment | ]