jlm-blog
~jlm

25-Aug-2018

Open source CPUs are not new

Filed under: general — jlm @ 23:25

There’s this video going around “An Open Source CPU!?” about SiFive’s implementation of RISC-V being “an open source CPU”, but it’s so duplicitous that I wanted to tear out my hair as I watched it. RISC-V is an interesting and worthy project, but the video is misleading in so many ways it’s hard to know where to begin.

For one thing, the x86-16 ISA wasn’t just hacked up in a few weeks from nothing. Intel’s architects spent months on it, and it was based on Intel’s 8-bit 8080 ISA, which was in turn informed by the experience of their earlier 8008 ISA. It had also already been on the market for a few years by the time IBM got around to the PC. For another thing, the x86-32 ISA was hardly lacking competition during its era of desktop dominance, with Motorola’s 65000, IBM’s Power Architecture, and DEC’s Alpha all big-name-backed ISAs trying to displace it. When the time came for 64-bit PCs, even Intel itself failed in its attempt to push a new kind of ISA for the PC market with its Itanium architecture.

Regarding the RISC/CISC divide, it is true that CISC processors don’t execute their ISA instructions directly in hardware now, but instead run RISC microcode (because RISC instruction-handling circuitry executes faster and is easier to design) for a CISC ISA interpreter. But that doesn’t mean RISC is best for application or system code, because microcode has no instruction cache! In the embedded systems and mobile-device markets, ARM had to abandon the “elegant” simplicity of their RISC ISA and supplement it with non-RISC “Thumb” and then “Thumb-2” extensions to raise its code density (important on small processors with small instruction caches) to keep x86 ISA microcontrollers, with their dense CISC code and ever-decreasing prices, at bay. As is often the case when competing technologies butt heads, the best solution is to find a way to use the advantages of both!

The video’s title is “An Open Source CPU!?” — and this is its biggest lie, because SiFive’s CPU being open is presented as something new, which is very much not true. Even if you dismiss all CISC designs as unworthy, there are open RISC specs with open source implementations that predate RISC-V, both grassroots and of commercial origin. Furthermore, SiFive’s CPU not only isn’t the first open source RISC processor, it’s not even the first open source RISC-V processor! You can get open source implementations of RISC-V here (VexRiscv) or here (ORCA) or here (Sodor).

This video is just an advertisement of SiFive’s pretending to be an independent informational video, spreading misinformation about the history and present state of microprocessors. (For your amusement, go and pause the video around 6m12s — the presenter is stating the inferiority of other open ISAs compared to RISC-V while showing a changelog on GitHub. But the changelog shown is not that of anything to do with another ISA, but the opposite: it’s actually the changelog for the port of gdb to RISC-V! The presenter could have grabbed a screenshot from the GitHub pages of the ZPU project with insignificant additional effort and shown something that was actually applicable to his claim, but once you’ve stepped off the straight-and-narrow path of honesty onto the wide highway of dishonesty, why bother?)

In short, that video is complete and utter BS, the presenter should be downvoted into YouTube oblivion, you should never pay one red cent for anything from SiFive, and RISC-V deserves better. It’s strong enough that it should be able to fight honestly, and having its proponents descend to dishonest shilling for one corporation is disgraceful.

11-Sep-2017

EBUSY: Another decade, and still sucking

Filed under: general, linux, programming — jlm @ 12:40

Today’s xkcd riffs a common frustration about busy files: programs that can’t do their intended operations on them rarely (if ever) specify the file that’s busy or tell the user which programs are using the file — and without that knowledge, the user can’t fix the problem.

There are tools that can help you discover those things, as I describe using ten years ago, but I’d already been running into EBUSY problems for ten years by then, and the old guard before me for another ten years beyond that. Why haven’t things improved?

Sometimes file_operation(filename) fails — hey, this happens, busy files are a thing, ain’t nothing your program can do about that. But report to the user that file_operation on filename failed for reason strerror(errno)! Not reporting the filename is just sloppy programming.

It’s not like the tools have gotten any better. What, you think it’s acceptable to make the user trace your program, looking through a haystack of every system call to find the needle which is the program’s critical failure? Is that work you’re putting on the user’s shoulders less than sticking the filename in the error message? This has sucked for two generations now. Please help making it suck less.

10-May-2007

Tip: compression

Filed under: general — jlm @ 16:28

It doesn’t help to zip already compressed file formats, like jpeg or mpeg, it only wastes CPU. Uncompressed video, audio, or still images will compress better with algorithms which are dedicated for video, audio, or images than they will with general compressors. JPEG is for photos — for images which are line drawings use PNG.

7-Mar-2006

Dvorak HOWTO

Filed under: general — jlm @ 18:37

[Dvorak key layout]

No, it won’t make you type faster (or probably not by much… top speed typists all use Dvorak, but I didn’t notice any improvement) or more “cheaply”, but it is easier on your hands, and reducing finger fatigue makes it a clear winner in my book.

How to switch:
Windows NT:
    Start ➙ Settings ➙ Control Panel ➙ Keyboard ➙ Input Locales ➙ Properties ➙ Keyboard Layout ➙ US-Dvorak
    Hit “OK”, then “Apply”.

Windows 9x:
    Same, but you’ll probably need to insert the install CD when it says, as the layout isn’t part of the default install, so have it ready.

Windows XP:
    Start ➙ Control Panel ➙ Regional and Language Options ➙ Languages ➙ Details ➙ Settings ➙ Default Input Language ➙ United States-Dvorak
    If it’s not availabe, under “Settings” go to Installed Services ➙ Keyboard ➙ Add and select it, then you’ll be able to set it as the default.

Linux console:
    “loadkeys dvorak” will change the current keymap to Dvorak. (Or sometimes “loadkeys dvorak/dvorak”, look around /lib/kbd/keymaps.) Making it the default usually involves setting the “KEYTABLE” attribute in /etc/sysconfig/keyboard to whatever you used with loadkeys.

X11 on PCs:
    xmodmap pentdvor.xmod

X11 on Sun 5x keyboards:
    xmodmap sun5dvor.xmod

Other X11:
    First, run xmodmap -pke > qwerty.xmod so you have the current keymap safely saved in case things get messed up. You’ll want to copy “xmodmap qwerty.xmod” into a cut buffer so you can paste it with only the mouse.
    Run xmodmap q2d.xmod
    This maps the Qwerty keysyms to Dvorak, and can fail sometimes, like if two keycodes generate one of the moved keysyms. Because it operates on keysyms, not keycodes, this file will rearrange your keyboard again if you run it twice, producing garbage. Good thing you have that recovery command in the cut buffer, right?
    You can save the keymap you produce with q2d with “xmodmap -pke > dvorak.xmod” and return to it with “xmodmap dvorak.xmod” after that. If you’re not quite happy with it, you can tweak the xmod file yourself, or get the “xkeycaps” program which will do it for you.

9-Sep-2005

Big screens

Filed under: general — jlm @ 09:53

I promised you a more upbeast post, so here it is…

Work recently gave me two very nice LCD monitors to replace those I’d been using before. 24″ TFT from Dell.

“Unfortunately”, the graphics card in the desktop I had (which I’d been using since getting hired) couldn’t drive these things, so they gave me a HP xw4200 to replace my xw4100, double the RAM and faster processor.

Now my computer can display on my monitors, but side by side things are very wide. But, these monitors can rotate on their stands! (Couldn’t do that with my old ones.) So, I want them vertical and side by side. Well, someone else had done the hard work of figuring out how to make that work, so I went and followed his lead. The distillation of that came down to:

  • Install the x.org X server (this deserves a post in itself)
  • Edit xorg.conf, turning off Xinerama and turning on xrandr (for now they’re incompatible):
    • In the “Device” Section, add Option "NoTwinViewXineramaInfo" "on"
      and Option "RandRRotation" "on"
    • Change TwinViewOrientation to “Above” or “Below”
    • In the “ServerLayout” Section, add Option "Xinerama" "off"
  • Put xrandr -o left at the start of your .xsession

Before and after screen shots at 1/8 scale:
[before]

[after]

I finally have enough space to have all the xterms I want! I’ve been trying to reach this state since forever, first with screen then with just piling the xterms onto all the real estate I could get. I don’t have to drop context and have space left over now. It’s surprising how good this feels– It’s this slight pressure that I never really noticed, the small frustation of having to look for somewhere to type– gone.

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