Slashdot is powered by your submissions, so send in your scoop


Forgot your password?

Comment: Great news (Score 1) 46

by AaronW (#49565947) Attached to: Imagination To Release Open MIPS Design To Academia

This is great news. When I was in college the microprocessor design class used a variant of MIPS though this started the quarter after I took the class. In my class we had to wire-wrap a 16-bit MIPS-like CPU using discrete chips and a couple programmable ones. MIPS is relatively easy to implement for educational purposes due to the simple instruction encoding and clean architecture. MIPS, unlike some other processors like ARM, also allows you to add your own instructions using coprocessor 2 which can be a great way to differentiate a processor and enhance it for different tasks. MIPS is a much simpler design compared to ARM or even PowerPC. MIPS is still widely used, especially in networking devices.

For example, my current employer has added a lot of instructions useful for encryption and hashing as well as some useful atomic instructions.

The move from 32-bits to 64-bits is actually quite clean on MIPS which did not require any major changes to the instruction set other than adding 64-bit instructions and sign-extending the 32-bit instructions. There are a few warts on it, such as the fact that the instruction following a branch instruction is always executed (SPARC is the same way). This is no longer all that useful with modern superscalar architectures and the branch delay slot can't always be filled with something useful. Things are also a bit cramped for 32-bits since only the lower 2GB of memory is available for user-space. Kernel space (KSEG0) is from 0x80000000-0x9fffffff and an uncached copy is at 0xa0000000-0xbfffffff. 0xC0000000 - 0xDFFFFFFF can be mapped using the translation look-aside buffer, making another 512MB available to the kernel. Both of these address ranges map directly to the lower 512MB of RAM which somewhat limits things. In 64-bit mode this isn't a problem though since all addresses are sign-extended. Another nice feature in kernel mode is that all physical addresses can be directly accessed, without requiring any special mapping other than setting bit 63 to 1.

Most MIPS processors do not use a hardware page table walker, instead relying on a software configured translation look-aside buffer. When there's a page miss, a quick interrupt occurs to replace an entry in that table with some hardware assist. This goes back to the original philosophy of keeping the hardware design simple. Due to the way it works, it allows total freedom with how page tables are represented in the operating system though there can be a slightly bigger overhead compared to hardware page tables.

The instruction set is quite clean and the instruction encodings are quite simple with only a few classes of instructions, unlike ARM64. Instruction decoding can be handled with only a few look-up tables. MIPS assembly language is far simpler and straight forward than, say X86 and it's quite mature, though not all processors implement all instructions. Many embedded MIPS processors lack floating point and the multimedia extensions, and many are 32-bit only. This helps cut cost and power when making chips for devices that don't need these features. MIPS also can scale up nicely. For example, the chips I work with currently scale up to 48 cores per chip and with two chips running in tandem Linux runs on 96 cores, all with a coherent cache. The newer ABIs are nice in that the only real difference between N32 and N64 is that pointers are 64-bits instead of 32-bits, just about everything else is the same so you get all of the features of 64-bit registers but keep the compactness of 32-bit pointers. This has been present for many years and is a fairly recent addition to X86 and ARM.

Comment: Re:Content Expert (Score 1) 334

by phantomfive (#49565339) Attached to: The Future Deconstruction of the K-12 Teacher

Once you are a full teacher, it takes a basic test to be able to teach other subjects. As in, so basic that back when I was in high school, if I were a licensed teacher, there were no subjects I looked at that I'd be unable to teach.

That doesn't sound like being a 'content expert.' Unless you count getting an education degree to be a content expert. And don't get me wrong, teachers do need expertise, it's not an easy job, but not necessarily in the subject they are teaching.

Comment: Re:You're not willing to pay (Score 1) 261

There's also the cost of production and non-economic price manipulation. Where I am, water is pulled out of the Mississippi, purified, and distributed, while there are no corresponding rivers of diamonds. Diamond prices are kept artificially high, while city water departments may not charge the full cost. You are considering demand here, not supply or market manipulation.

Comment: Re:Why I refused to sign up (Score 1) 337

by david_thornley (#49564283) Attached to: Google Insiders Talk About Why Google+ Failed

Also, I use Facebook because a lot of my friends and family are on it, and it's a reasonably good way of staying in touch. I have no real use for a social network except to maintain contact with people I want to be sociable with, and unless a large number of friends and family moved over to Google+ it wasn't worth my attention.

Comment: Re:A short, speculative cautionary tale... (Score 1) 399

by bluefoxlucid (#49564165) Attached to: Using Adderall In the Office To Get Ahead

The American educational system has been dragged through the mud for the last 40+ years over the idea that all children can be geniuses.

We have cut and cut and cut. Some kids are "gifted", and get to take Calculus; algebra is no longer standard curriculum. English grammar has been cut back. Latin and Greek are too hard for the less-special of us.

The school system is targeting "success", in that "we can all succeed", by lowering the fucking bar.

Comment: Re:Engineering is a team activity (Score 1) 118

by david_thornley (#49564085) Attached to: When Exxon Wanted To Be a Personal Computing Revolutionary

Engineering isn't usually done by intense collaboration for eight-plus hours a day. There is a need for solitary time, or at least small-group time, and so if we schedule all the all-hands collaboration at well-chosen times we can accommodate people coming in at a fairly wide range of times. This does not mean you want an engineer going off in some weird direction without supervision or collaboration, but that you don't need to have everybody on the exact same schedule. This is useful, since not all people work best at the same times.

Software people, anyway, have a fairly clear idea of stuff that helps them do quality work, and stuff that doesn't, and they tend to be rather intolerant of requirements that don't, in their opinion, help their work. Nowadays, if you impose a dress code on your software people, or a rigid schedule, you'll have problems attracting and retaining good people.

Comment: Re:The religion of peace ladies and gentlemen (Score 1) 476

Like most wars, the causes for the Crusades were pretty complex, and not limited to the desire to protect pilgrims.

Also, you'll find that plenty of winners hold on to grudges, particularly when they were invaded in the first place. China and the Soviet Union won WWII, France won WWI, and so on back. It didn't stop them bitching about the Japanese and Germans.

Comment: Re:truly an inspiration. (Score 1) 476

You're overgeneralizing. There's tens of millions of Christians in the US who believe that the Bible is literally true, and that Christian morality (or, rather, their version of it, which AFAICT differs from what Jesus said) should be enshrined in law. This is not a tiny subset, particularly as (unlike most Christians) they tend to be politically active about enforcing their beliefs.

"Consequences, Schmonsequences, as long as I'm rich." -- Looney Tunes, Ali Baba Bunny (1957, Chuck Jones)