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• Programming Language Levels

  20 mai 2011, par Multimedia Mike — Programming

  I’ve been doing this programming thing for some 20 years now. Things sure do change. One change I ponder from time to time is the matter of programming language levels. Allow me to explain.

  The 1990s
  When I first took computer classes in the early 1990s, my texts would classify computer languages into 3 categories, or levels. The lower the level, the closer to the hardware ; the higher the level, the more abstract (and presumably, easier to use). I recall that the levels went something like this :

  • High level : Pascal, BASIC, Logo, Fortran
  • Medium level : C, Forth
  • Low level : Assembly language

  Keep in mind that these were the same texts which took the time to explain the history of computers from mainframes -> minicomputers -> a relatively recent phenomenon called microcomputers or "PCs".

  Somewhere in the mid-late 1990s, when I was at university, I was introduced to a new tier :

  • Very high level : Perl, shell scripting

  I think there was some debate among my peers about whether C++ and Java were properly classified as high or very high level. The distinction between high and very high, in my observation, seemed to be that very high level languages had more complex data structures (at the very least, a hash / dictionary / associative array / key-value map) built into the language, as well as implicit memory management.

  Modern Day
  These days, the old hierarchy is apparently forgotten (much like minicomputers). I observe that there is generally a much simpler 2-tier classification :

  • Low level : C, assembly language
  • High level : absolutely every other programming language in wide use today

  I find myself wondering where C++ and Objective-C fit in this classification scheme. Then I remember that it doesn’t matter and this is all academic.

  Relevancy
  I think about this because I have pretty much stuck to low-level programming all of my life, mostly due to my interest in game and multimedia-type programming. But the trends in computing have favored many higher level languages and programming paradigms. I woke up one day and realized that the kind of work I often do — lower level stuff — is not very common.

  I’m not here to argue that low or high level is superior. You know I’m all about using the appropriate tool for the job. But I sometimes find myself caught between worlds, having the defend and explain one to the other.

  • On one hand, it’s not unusual for the multitudes of programmers working at the high level to gasp and wonder why I or anyone else would ever use C or assembly language for anything when there are so many beautiful high level languages. I patiently explain that those languages have to be written in some other language (at first) and that they need to run on some operating system and that most assuredly won’t be written in a high level language. For further reading, I refer them to Joel Spolsky’s great essay called Back to Basics which describes why it can be useful to know at least a little bit about how the computer does what it does at the lowest levels.
  • On the other hand, believe it or not, I sometimes have to defend the merits of high level languages to my low level brethren. I’ll often hear variations of, "Any program can be written in C. Using a high level language to achieve the same will create a slow and bloated solution." I try to explain that the trade-off in time to complete the programming task weighed against the often-negligible performance hit of what is often an I/O-bound operation in the first place makes it worthwhile to use the high level language for a wide variety of tasks.

    Or I just ignore them. That’s actually the best strategy.

• Metal Gear Solid VP3 Easter Egg

  4 août 2011, par Multimedia Mike — Game Hacking

  Metal Gear Solid : The Twin Snakes for the Nintendo GameCube is very heavy on the cutscenes. Most of them are animated in real-time but there are a bunch of clips — normally of a more photo-realistic nature — that the developers needed to compress using a conventional video codec. What did they decide to use for this task ? On2 VP3 (forerunner of Theora) in a custom transport format. This is only the second game I have seen in the wild that uses pure On2 VP3 (first was a horse game). Reimar and I sorted out most of the details sometime ago. I sat down today and wrote a FFmpeg / Libav demuxer for the format, mostly to prove to myself that I still could.

  Things went pretty smoothly. We suspected that there was an integer field that indicated the frame rate, but 18 fps is a bit strange. I kept fixating on a header field that read 0x41F00000. Where have I seen that number before ? Oh, of course — it’s the number 30.0 expressed as an IEEE 32-bit float. The 4XM format pulled the same trick.

  Hexadecimal Easter Egg
  I know I finished the game years ago but I really can’t recall any of the clips present in the samples directory. The file mgs1-60.vp3 contains a computer screen granting the player access and illustrates this with a hexdump. It looks something like this :

  
  
  

  Funny, there are only 22 bytes on a line when there should be 32 according to the offsets. But, leave it to me to try to figure out what the file type is, regardless. I squinted and copied the first 22 bytes into a file :

   1F 8B 08 00   85 E2 17 38   00 03 EC 3A   0D 78 54 D5
   38 00 03 EC   3A 0D
  

  And the answer to the big question :

  $ file mgsfile
  mgsfile : gzip compressed data, from Unix, last modified : Wed Oct 27 22:43:33 1999
  

  A gzip’d file from 1999. I don’t know why I find this stuff so interesting, but I do. I guess it’s no more and less strange than writing playback systems like this.

• Notes on Linux for Dreamcast

  23 février 2011, par Multimedia Mike — Sega Dreamcast, VP8

  I wanted to write down some notes about compiling Linux on Dreamcast (which I have yet to follow through to success). But before I do, allow me to follow up on my last post where I got Google’s libvpx library decoding VP8 video on the DC. Remember when I said the graphics hardware could only process variations of RGB color formats ? I was mistaken. Reading over some old documentation, I noticed that the DC’s PowerVR hardware can also handle packed YUV textures (UYVY, specifically) :

  
  
  

  The video looks pretty sharp in the small photo. Up close, less so, due to the low resolution and high quantization of the test vector combined with the naive chroma upscaling. For the curious, the grey box surrounding the image highlights the 256-square texture that the video frame gets plotted on. Texture dimensions have to be powers of 2.

  Notes on Linux for Dreamcast
  I’ve occasionally dabbled with Linux on my Dreamcast. There’s an ancient (circa 2001) distro based around a build of kernel 2.4.5 out there. But I wanted to try to get something more current compiled. Thus far, I have figured out how to cross compile kernels pretty handily but have been unsuccessful in making them run.

  Here are notes are the compilation portion :
  

  • kernel.org provides a very useful set of cross compiling toolchains
  • get the gcc 4.5.1 cross toolchain for SH-4 (the gcc 4.3.3 one won’t work because the binutils is too old ; it will fail to assemble certain instructions as described in this post)
  • working off of Linux kernel 2.6.37, edit the top-level Makefile ; find the ARCH and CROSS_COMPILE variables and set appropriately :

    ARCH ?= sh
    CROSS_COMPILE ?= /path/to/gcc-4.5.1-nolibc/sh4-linux/bin/sh4-linux-
    

  • $ make dreamcast_defconfig
  • $ make menuconfig ... if any changes to the default configuration are desired
  • manually edit arch/sh/Makefile, changing :

    cflags-$(CONFIG_CPU_SH4) := $(call cc-option,-m4,) \
            $(call cc-option,-mno-implicit-fp,-m4-nofpu)
    

    to :

    cflags-$(CONFIG_CPU_SH4) := $(call cc-option,-m4,) \
            $(call cc-option,-mno-implicit-fp)
    

    I.e., remove the '-m4-nofpu' option. According to the gcc man page, this will "Generate code for the SH4 without a floating-point unit." Why this is a default is a mystery since the DC’s SH-4 has an FPU and compilation fails when enabling this option.

  • On that note, I was always under the impression that the DC sported an SH-4 CPU with the model number SH7750. According to this LinuxSH wiki page as well as the Linux kernel help, it actually has an SH7091 variant. This photo of the physical DC hardware corroborates the model number.
  • $ make ... to build a Linux kernel for the Sega Dreamcast

  Running
  So I can compile the kernel but running the kernel (the resulting vmlinux ELF file) gives me trouble. The default kernel ELF file reports an entry point of 0x8c002000. Attempting to upload this through the serial uploading facility I have available to me triggers a system reset almost immediately, probably because that’s the same place that the bootloader calls home. I have attempted to alter the starting address via ’make menuconfig’ -> System type -> Memory management options -> Physical memory start address. This allows the upload to complete but it still does not run. It’s worth noting that the 2.4.5 vmlinux file from the old distribution can be executed when uploaded through the serial loader, and it begins at 0x8c210000.