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Broadcom Releases Source For Graphics Stack; Raspberry Pi Sets Bounty For Port

david.given Not actually sou (77 comments)

The Videocore IV on the Raspberry Pi (which totally kicks arse, BTW, it's a beautiful, beautiful processor. Did you know it's dual core?) currently doesn't have an open source compiler that's any good[*] which I'm aware of. I have tried porting gcc, and got a reasonable way into it, but ground to a halt because gcc. I know another guy who's similarly about half-way through an LLVM port. And Volker Barthelmann's excellent vbcc compiler has a VC4 prototype which makes superb code, but that's not open source at all.

Without a compiler, obviously the source isn't much good, although the VC4-specific code is really interesting to look through.

In addition, having done a really brief scan of the docs they've released, this isn't what the article's implying: what we've got here looks like the architecture manual for the QPU and the 3D engine. The QPU is the shader engine. Don't get me wrong, this is awesome, and will allow people to do stuff like compile their own shaders and do an OpenCL port, but I haven't seen any documentation relating to the VideoCore IV processor. The binary blob everyone complains about runs on that.

It does looks like the source dump contains a huge pile of stuff for the VC4, so maybe they're going to release more later. But even incomplete, this is a great step forward, and much kudos to Broadcom for doing this.

[*] I have done a really crap port of the Amsterdam Compiler Kit compiler for the VC4. It generates terrible, terrible code, but I have got stuff running on the Raspberry Pi bare metal. It's all rather ground to a halt because there's still a lot of stuff to figure out in the boot process, but interested parties may wish to visit http://cowlark.com/piface.

about a month and a half ago

Kentucky: Programming Language = Foreign Language

david.given Excellent news (426 comments)

This move makes absolutely perfect sense. Soon, everyone graduating from Kentucky high schools will have above average academic qualifications. Also, the senator is a genius and extremely good looking.

about 3 months ago

SpaceX Wins Use of NASA's Launch Pad 39A

david.given Re:Watch out (99 comments)

...actually, I misread the chart. GEO is 3.8km/s from LEO. Lunar orbit is 2.4km/s if you transfer from GEO, giving a total of 6.2km/s. If you go straight from LEO to lunar orbit, it's only 4.1km/s... barely more than GEO. So, yeah, I reckon a technology demonstrator is definitely doable right now.

about 4 months ago

SpaceX Wins Use of NASA's Launch Pad 39A

david.given Re:Watch out (99 comments)

Even better --- they've just demonstrated the ability to go to GEO, which is about 14km/s from the Earth's surface. Lunar orbit is only another 2.4km/s, and the moon's surface another 1.6 on top of that!

Chances are that with the technology they have right now, that is, using a modified F9 with the GEO upper stage, they could send a probe on a free-return trajectory to the moon. Or even easier, an impactor. I suspect they won't; Elon Musk appears to have his sights firmly set on the upgraded F9 Heavy and the rocket-landing Dragon, and with that setup you could probably remote land a complete Dragon capsule. I'd be really interested to know what sort of delta vee the Dragon's internal rockets will have...

about 4 months ago

Chinese Lunar Probe Lands Successfully

david.given Re:First (250 comments)

As an interesting addendum:

Luna-9's pictures were sent back using one of the standard encodings used for wireless newspaper photography transmission. During the transmission, the Jodrell Bank radio telescope in the United Kingdom was listening in (well, wouldn't you?) and the astronomers there recognised the encoding, phoned someone at the Daily Express, and as a result the first pictures from the surface of the moon ever were printed in a British newspaper while the USSR was still wondering what to do with them.

There is some speculation that the encoding scheme was picked deliberately to make sure this happened...

about 4 months ago

Chang'e-3 Lunar Rover Landing Slated For 13:40 UTC Saturday

david.given Successfully landed (90 comments)

CCTV's live coverage showed a textbook landing and solar array deployment, including some very shiny live pictures from the descent imager. Next steps are self-testing, instrument deployment and releasing the rover, which they've said will take up to 24 hours. Although I'd imagine that they'll release images from the panoramic mast camera as soon as possible.

about 4 months ago

Dual-Core Allwinner A20 Powered EOMA-68 Engineering Card Available

david.given Re:Lets try to clear up some missinformation here (98 comments)

The RPi is an ARMv6, while this (along with pretty much every other modern ARM device) is an ARMv7. The ARMv6 has hardfloat but implements a slightly different version of the spec. Most OSes have standardised on the ARMv7 version which means that their code won't run on the ARMv6. So Debian armhf will run on this but will not run on the RPi: you have to use Raspbian instead, which is a version of Debian specifically compiled for the ARMv6. (Of course, Debian armel will run on both, but then you don't get any hardware floating point support.)

The Broadcom GPU is significantly awesome. It is, however, almost totally undocumented. There's a reverse engineering project which has mostly nailed down the instruction set, and there are even some C compilers for it (one of them is mine!) even though there's no gcc or LLVM support for it. You can write programs in C and run them on the bare metal. Unfortunately the GPU doesn't support double-precision float and the MMU is kinda weird, and it's probably going to be slower than the ARM for non-DSP-heavy code anyway, so it's unlikely you'll see Linux for it any time soon. But it's a beautiful, beautiful architecture to write code for. (And it's dual core! Not very many people know that...)

about 5 months ago

Duke Univ. Device Converts Stray Wireless Energy Into Electricity For Charging

david.given Re:Units! (216 comments)

Back in 2009, a UK artist set up an... installation, I suppose you'd call it... which was 1301 flourescent lighting tubes in a field under a 400kV megagrid power line. It's worth checking the pictures out, as they're actually quite striking:


The total amount of power used here would be negligible, of course. But I'm surprised they didn't come down on him for improper disposal of mercury...

about 5 months ago

First New Top-Level Domains Added To the Root Zone

david.given Re:It's "site", not "sale" (106 comments)

No wonder I find most of the posts incomprehensible! I'm reading it in ISO 8859-15...

about 6 months ago

The Grasshopper Can Fly Sideways

david.given Re:Gravity pulls toward the Earth (127 comments)

Note that in real life you do the gravity roll much earlier than you do in KSP --- this is to get the vehicle clear of the launchpad so that if you're not going to space today, the debris doesn't land on your technicians.

In KSP you leave the gravity roll quite late so that you waste as little fuel as possible pushing through the dense part of the atmosphere (I usually do it at 15km).

about 8 months ago

Ask Slashdot: Light-Footprint Antivirus For Windows XP?

david.given Microsoft Security Essentials (294 comments)

Yes, seriously. It's lightweight, it's free, it's integrated into Windows Update so it's really easy to get updates, and best of all it doesn't continually hassle you and go LOOK AT ME! LOOK AT ME! the way most of the other antivirus apps do. It just sits in your icon bar and does its job.

It's not brilliant, security-wise --- it's merely adequate --- but if you want something that hides itself away and gets on with things with a minimum of user panic, it's definitely the way to go.

about 9 months ago

Volkswagen Concept Car Averages 262 MPG

david.given Re:Proper units (353 comments)

I will see your pedantry, and raise you more pedantry: the stone is defined as 14 avoirdupois pounds; one avoirdupois pound is defined as 0.45359237 kg; therefore the stone is a unit of mass.

Yes, I was disappointed too. Still, we'll always have tons (which depending on the usage can be weight, mass, volume, energy, or power).

about 9 months ago

Bitcoin Exchange Mt. Gox Halts USD Withdrawals

david.given Re:Threat ? Hilarious. (173 comments)

Her son Todd has taken over. Apparently they're not bad, although I stopped reading new Pern books years ago.

about 10 months ago

Bitcoin Exchange Mt. Gox Halts USD Withdrawals

david.given Re:Threat ? Hilarious. (173 comments)

...Bitcoin is posing as a "thread" is hilarious on it's face.

Bitcoin raining down from the Red Star, threatening to destroy all life on our planet, and only an elite squad of fire-breathing US drone fighter aircraft can save us? I agree that this does seem a little hard to believe.

about 10 months ago

Writer Jack Vance Dead At 96

david.given Re:Vance was a giant in the field (83 comments)

Oh, _The Moon Moth_ is brilliant. There's a (slightly mangled; there's a repeated section in the middle, but all the text is present) dodgy copy online here:


Definitely worth a read. (Apparently it's been adapted to a graphic novel; it seems a shame to miss out on the Vancian prose, though.)

Personally I have a soft spot for the Demon Princes novels. Classic tales of revenge, with a twist; you don't realise quite how much characterisation Vance sneaks in until after you've read them. Must reread...

about a year ago

New Best Way To Nuke a Short-Notice Asteroid

david.given Re:Simulate or it didn't happen! You know what I m (311 comments)

I have heard that this is actually <i>worse</i> --- because the smaller fragments are more efficient at transferring heat to the atmosphere, while a single big impact will absorb a lot of energy into the crust and reflect a bunch more into space. So an asteroid-sized dust cloud hitting the Earth at 11km/s stands a good chance of igniting every flammable object in a thousand kilometre radius. But I can't find a reference for that.

about a year ago

New Best Way To Nuke a Short-Notice Asteroid

david.given Re:Simulate or it didn't happen! You know what I m (311 comments)

No, they wouldn't --- acceleration due to gravity is independent of the mass of the body. (The force due to gravity is GMm/r^2; acceleration is a=F/m; therefore the acceleration due to gravity is GMm/mr^2. The two m factors cancel out.)

What would happen is the nuke would push the fragments apart. These would continue to diverge, but would follow much the same course as the original asteroid. Whether they've been deflected enough to miss the Earth --- which is, of course, a really big target --- depends entirely on how hard the nuke pushed them and how long they travel before impact.

about a year ago

Space Station Crew Prepare For Emergency Spacewalk

david.given Re:Live Footage! (95 comments)

In order for the station to reenter, you'd have to change its orbital velocity by a substantial amount. The interwebs suggests that it's about 150m/s (that's about 300 mph for the metrically challenged).

To change the ISS's velocity that much in a single impact would destroy the entire station. I don't even think the ISS is capable of being deorbited without additional hardware; the Progress supply drones it currently uses to adjust its orbit carry very little thruster fuel. (Just enough to deorbit the Progress itself, plus some spare.)

Personally, the main bit which caused me to roll my eyes is right at the beginning, where the two astronauts admire the sunset, tumbling uncontrollably, while facing in entirely the wrong direction...

about a year ago

Stop Standardizing HTML

david.given Re:language (302 comments)

Using words I recognize as nonsense isn't the sole problem. It's vocabulary collisions.

I had precisely this problem the other day, when talking to someone about DVCSes. It took about five minutes (of face-to-face conversation, mind; five minutes is a lot) to figure out that git and hg use the word 'revert' to refer to fundamentally different operations.

It would have been less confusing if he'd just said 'I don't know what that word means'. It was the fact that he thought he knew what I meant, but didn't, which was causing the problems...

about a year ago



Dr Robert Bussard dies

david.given david.given writes  |  more than 6 years ago

david.given writes "Dr Robert W. Bussard, nuclear physicist and fusion physics researcher, died from cancer on October 6. Most people here will know him for the Bussard Ramjet, a theoretical space drive that uses magnetic fields to scoop up interstellar hydrogen to power a fusion drive. In recent years he has been working on the Polywell electrostatic inertial confinement fusion reactor, which promises to produce a cheap and simple fusion power plant without the cost and complexity of magnetic confinement. Rumours are that the Polywell was recently funded by the US Navy and may start producing results in 2008."
Link to Original Source



This is another test of the journal system...

david.given david.given writes  |  about 9 years ago This is not a real journal entry. This is only a test. If this were a real journal entry, you would be reading this right now.

Hmm. Can I attach files? Or is it just plain text?

I seem to be able to edit them, too. That's quite handy.

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