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• 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.

• Dreamcast Anniversary Programming

  10 septembre 2010, par Multimedia Mike — Game Hacking

  This day last year saw a lot of nostalgia posts on the internet regarding the Sega Dreamcast, launched 10 years prior to that day (on 9/9/99). Regrettably, none of the retrospectives that I read really seemed to mention the homebrew potential, which is the aspect that interested me. On the occasion of the DC’s 11th anniversary, I wanted to remind myself how to build something for the unit and do so using modern equipment and build tools.

  
  
  

  Background
  Like many other programmers, I initially gained interest in programming because I desired to program video games. Not content to just plunk out games on a PC, I always had a deep, abiding ambition to program actual video game hardware. That is, I wanted to program a purpose-built video game console. The Sega Dreamcast might be the most ideal candidate to ever emerge for that task. All that was required to run your own software on the unit was the console, a PC, some free software tools, and a special connectivity measure.

  The Equipment
  Here is the hardware required (ideally) to build software for the DC :

  • The console itself (I happen to have 3 of them laying around, as pictured above)
  • Some peripherals : Such as the basic DC controller, the DC keyboard (flagship title : Typing of the Dead), and the visual memory unit (VMU)
    
    
    
  • VGA box : The DC supported 480p gaming via a device that allowed you to connect the console straight to a VGA monitor via 15-pin D-sub. Not required for development, but very useful. I happen to have 3 of them from different third parties :
    
    
    
  • Finally, the connectivity measure for hooking the DC to the PC.
    There are 2 options here. The first is rare, expensive and relatively fast : A DC broadband adapter. The second is slower but much less expensive and relatively easy to come by– the DC coder’s cable. This was a DB-9 adapter on one end and a DC serial adapter on the other, and a circuit in the middle to monkey with voltage levels or some such ; I’m no electrical engineer. I procured this model from the notorious Lik Sang, well before that outfit was sued out of business.
    
    
    

  Dealing With Legacy
  Take a look at that coder’s cable again. DB-9 ? When was the last time you owned a computer with one of those ? And then think farther back to the last time to had occasion to plug something into one of those ports (likely a serial mouse).

  
  
  

  A few years ago, someone was about to toss out this Belkin USB to DB-9 serial converter when I intervened. I foresaw the day when I would dust off the coder’s cable. So now I can connect a USB serial cable to my Eee PC, which then connects via converter to a different serial cable, one which has its own conversion circuit that alters the connection to yet another type of serial cable.

  Bits is bits is bits as far as I’m concerned.

  
  
  

  Putting It All Together
  Now to assemble all the pieces (plus a monitor) into one development desktop :

  
  
  

  The monitor says “dcload 1.0.3, idle…”. That’s a custom boot CD-ROM that is patiently waiting to receive commands, code and data via the serial port.

  Getting The Software
  Back in the day, homebrew software development on the DC revolved around these components :

  • GNU binutils : for building base toolchains for the Hitachi SH-4 main CPU as well as the ARM7-based audio coprocessor
  • GNU gcc/g++ : for building compilers on top of binutils for the 2 CPUs
  • Newlib : a C library intended for embedded systems
  • KallistiOS : an open source, real-time OS developed for the DC

  The DC was my first exposure to building cross compilers. I developed some software for the DC in the earlier part of the decade. Now, I am trying to figure out how I did it, especially since I think I came up with a few interesting ideas at the time.

  Struggling With the Software Legacy
  The source for KallistiOS has gone untouched since about 2004 but is still around thanks to Sourceforge. The instructions for properly building the toolchain have been lost to time, or would be were it not for the Internet Archive’s copy of a site called Hangar Eleven. Also, KallistiOS makes reference to a program called ‘dc-tool’ which is needed on the client side for communicating with dcload. I was able to find this binary at the Boob ! site (well-known in DC circles).

  I was able to build the toolchain using binutils 2.20.1, gcc 4.5.1 and newlib 1.18.0. Building the toolchain is an odd process as it requires building the binutils, then building the C compiler, then newlib, and then building the C compiler again along with the C++ compiler because the C++ compiler depends on newlib.

  With some effort, I got the toolchain to build KallistiOS and most of its example programs. I documented most of the tweaks I had to make, several of them exactly the same as this one that I recently discovered while resurrecting a 10-year-old C program (common construct in C programming of old ?).

  Moment of Truth
  So I had some example programs built as ELF files. I told dc-tool to upload and run them on the waiting console. Unfortunately, the tool would just sort of stall, though some communication had evidently taken place. It has been many years since I have seen this in action but I recall that something more ought to be happening.

  Plan B (Hardware)
  This is the point that I remember that I have been holding onto one rather old little machine that still has a DB-9 serial port. It’s not especially ergonomic to set up. I have to run it on my floor because, to connect it to my network, I need to run a 25′ ethernet cable that just barely reaches from the other room. The machine doesn’t seem to like USB keyboards, which is a shame since I have long since ditched any PS/2 keyboards. Fortunately, the box still has an old Gentoo distro and is running sshd, a holdover from its former life as a headless box.

  
  
  

  Now when I run dc-tool, both the PC and DC report the upload progress while pretty overscan bars oscillate on the DC’s monitor. Now I’m back in business, until…

  Plan C (Software)
  None of these KallistiOS example programs are working. Some are even reporting catastrophic failures (register dumps) via the serial console. That’s when I remember that gcc can be a bit fickle on CPU architectures that are not, shall we say, first-class citizens. Back in the day, gcc 2.95 was a certified no-go for SH-4 development. 3.0.3 or 3.0.4 was called upon at the time. As I’m hosting this toolchain on x86_64 right now, gcc 3.0.4 can’t even be built (predates the architecture).

  One last option : As I searched through my old DC project directories, I found that I still have a lot of the resulting binaries, the ones I built 7-8 years ago. I upload a few of those and I finally see homebrew programming at work again, including this old program (described in detail here).

  Next Steps
  If I ever feel like revisiting this again, I suppose I can try some of the older 4.x series to see if they build valid programs. Alternatively, try building an x86_32-hosted 3.0.4 toolchain which ought to be a known good. And if that fails, search a little bit more to find that there are still active Dreamcast communities out there on the internet which probably have development toolchain binaries ready for download.

• How to use ffmepg create video from some bitmaps(the format is ARGB32) [closed]

  16 février 2013, par xiangyun

  I have some bitmaps(the format is ARGB32), I want use ffmepg to create video from this bitmaps, the video format is mp4, encoder video stream use H263.
  This is my frist time use ffmpeg ,I had read sample code in ffmpeg doc, but I still don't know how to create mp4 file from serial bitmaps. And I want use this native code in android app. Anybody who had experience on ffmepg can help or teach me ?