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• Dreamcast SD Adapter and DreamShell

  31 décembre 2014, par Multimedia Mike — Sega Dreamcast

  Nope ! I’m never going to let go of the Sega Dreamcast hacking. When I was playing around with Dreamcast hacking early last year, I became aware that there is such a thing as an SD card adapter for the DC that plugs into the port normally reserved for the odd DC link cable. Of course I wanted to see what I could do with it.

  The primary software that leverages the DC SD adapter is called DreamShell. Working with this adapter and the software requires some skill and guesswork. Searching for these topics tends to turn up results from various forums where people are trying to cargo-cult their way to solutions. I have a strange feeling that this post might become the unofficial English-language documentation on the matter.

  Use Cases
  What can you do with this thing ? Undoubtedly, the primary use is for backing up (ripping) the contents of GD-ROMs (the custom optical format used for the DC) and playing those backed up (ripped) copies. Presumably, users of this device leverage the latter use case more than the former, i.e., download ripped games, load them on the SD card, and launch them using DreamShell.

  However, there are other uses such as multimedia playback, system exploration, BIOS reprogramming, high-level programming, and probably a few other things I haven’t figured out yet.

  Delivery
  I put in an order via the dc-sd.com website and in about 2 short months, the item arrived from China. This marked my third lifetime delivery from China and curiously, all 3 of the shipments have pertained to the Sega Dreamcast.

  
  

  

  Click for larger image

  
  

  I thought it was very interesting that this adapter came in such complete packaging. The text is all in Chinese, though the back states “Windows 98 / ME / 2000 / XP, Mac OS 9.1, LINUX2.4”. That’s what tipped me off that they must have just cannibalized some old USB SD card readers and packaging in order to create these. Closer inspection of the internals through the translucent pink case confirms this.

  Usage
  According to its change log, DreamShell has been around for a long time with version 1.0.0 released in February of 2004. The current version is 4.0.0 RC3. There are several downloads available :

  1. DreamShell 4.0 RC 3 CDI Image
  2. DreamShell 4.0 RC 3 + Boot Loader
  3. DreamShell 4.0 RC 3 + Core CDI image

  Option #2 worked for me. It contains a CDI disc image and the DreamShell files in a directory named DS/.

  Burn the CDI to a CD-R in the normal way you would burn a bootable Dreamcast disc from a CDI image. This is open-ended and left as an exercise to the reader, since there are many procedures depending on platform. On Linux, I used a small script I found once called burncdi-dc.sh.

  Then, copy the contents of the DS/ folder to an SD card. As for filesystem, FAT16 and FAT32 are both known to work. The files in DS/ should land in the root of the SD card ; the folder DS/ should not be in the root.

  Plug the SD card into the DC SD adapter and plug the adapter in the link cable port on the back of the Dreamcast. Then, boot the disc. If it works, you will see this minor corruption of the usual Sega licensing screen :

  
  
  

  Then, there will be a brief white-on-black text screen that explains the booting process :
  

  
  
  

  Then, there will be the main DreamShell logo :

  
  
  

  Finally, you will land on the DreamShell main desktop :

  
  
  

  Skepticism
  At first, I was supremely skeptical of the idea that this SD adapter could perform speedily enough to play games reasonably. This was predicated on the observation that my DC coder’s cable that I used to use for homebrew development could not transfer faster than 115200 bits/second, amounting to about 11 kbytes/sec. I assumed that this was a fundamental limitation of the link port.

  In fact, I ripped a few of my Dreamcast discs over a decade ago and still have those rips lying around. So I copied the ISO image of Resident Evil : Code Veronica — the game I personally played most on the DC — to the SD card (anywhere works) and used the “ISO loader” icon seen on the desktop above to launch the game.

  It works :

  
  
  

  The opening FMV plays at full speed. Everything loads as fast as I remember. I was quite surprised.

  Digression : My assumptions about serial speeds have often been mistaken. 10 years ago, I heard stories about how we would soon be able to watch streaming video on our cell phones. I scoffed because I thought the 56K limitation of dialup modems was some sort of fundamental speed-of-light type of limitation for telephony bandwidth, wired or wireless.

  The desktop menu also includes a ‘speedtest’ tool that profiles the write and read performance of your preferred storage medium. For my fastest SD card (a PNY 2 GB card) :

  
  
  

  This is probably more representative of the true adapter bandwidth as reading and writing is a good deal faster through more modern interfaces on PC and Mac with this same card.

  Look at the other options on the speedtest console. Hard drive ? Apparently, it’s possible, but it requires a good deal more hardware hacking than just purchasing this SD adapter.

  Ripping
  As you can see from the Resident Evil screenshot, playing games works quite nicely. How about ripping ? I’m pleased to say that DreamShell has a beautiful ripping interface :

  
  
  

  Enter a name for the disc (or read the disc label), select the storage medium, and let it, well, rip. It indicates which track it’s working on and the Sega logo acts as a progress bar, shading blue as the track rip progresses.

  I’m finally, efficiently, archiving that collection of Sega Dreamcast demo discs ; I’m hoping they’ll eventually find a home at the Internet Archive. How is overall ripping performance ? Usually about 38-40 minutes to rip a full 900-1000 MB. That certainly beats the 27-28 hours that were required when I performed the ripping at 11 kbytes/sec via the DC coders cable.

  All is well until I get a sector reading error :

  
  
  

  That’s when it can come in handy to have 3 DC consoles (see ?! not crazy !).

  Other Uses
  There’s a file explorer. You can browse the filesystem of the SD card, visual memory unit, or the CD portion of the GD-ROM (would be more useful if it accessed the GD area). There are FFmpeg files included. So I threw a random Cinepak file and random MPEG-1 file at it to see what happens. MPEG-1 didn’t do anything, but this Cinepak file from some Sierra game played handily :

  
  
  

  If you must enter strings, it helps to have a Dreamcast keyboard (which I do). Failing that, here’s a glimpse of the onscreen keyboard that DreamShell equips :

  
  
  

  Learning to use it is a game in itself.

  There is an option of installing DreamShell in the BIOS. I did not attempt this. I don’t know if it’s possible (not like there’s a lot of documentation)– perhaps a custom BIOS modchip is needed. But here’s what the screen looks like :

  
  
  

  There is also a plain console to interact with (better have a physical keyboard). There are numerous file manipulation commands and custom system interaction commands. I see one interesting command called ‘addr’ that looks useful for dumping memory regions to a file.

  A Lua language interpreter is also built in. I would love to play with this if I could ascertain whether DreamShell provided Dreamcast-specific APIs.

  Tips And Troubleshooting
  I have 3 Dreamcast consoles, affectionately named Terran, Protoss, and Zerg after the StarCraft II stickers with which they are adorned. Some seem to work better than others. Protoss seemed to be able to boot the DreamShell disc more reliably than the others. However, I was alarmed when it couldn’t boot one morning when it was churning the previous day.

  I think the problem is that it was just cold. That seemed to be the issue. I put in a normal GD-ROM and let it warm up on that disc for awhile and then DreamShell booted fine. So that’s my piece of cargo-culting troubleshooting advice.

• Nexus One

  19 mars 2010, par Mans — Uncategorized

  I have had a Nexus One for about a week (thanks Google), and naturally I have an opinion or two about it.
  

  Hardware

  With the front side dominated by a touch-screen and a lone, round button, the Nexus One appearance is similar to that of most contemporary smartphones. The reverse sports a 5 megapixel camera with LED flash, a Google logo, and a smaller HTC logo. Power button, volume control, and headphone and micro-USB sockets are found along the edges. It is with appreciation I note the lack of a front-facing camera ; the silly idea of video calls is finally put to rest.

  Powering up the phone (I’m beginning to question the applicability of that word), I am immediately enamoured with the display. At 800×480 pixels, the AMOLED display is crystal-clear and easily viewable even in bright light. In a darker environment, the display automatically dims. The display does have one quirk in that the subpixel pattern doesn’t actually have a full RGB triplet for each pixel. The close-up photo below shows the pattern seen when displaying a solid white colour.

  

  The result of this is that fine vertical lines, particularly red or blue ones, look a bit jagged. Most of the time this is not much of a problem, and I find it an acceptable compromise for the higher effective resolution it provides.

  Basic interaction

  The Android system is by now familiar, and the Nexus offers no surprises in basic usage. All the usual applications come pre-installed : browser, email, calendar, contacts, maps, and even voice calls. Many of the applications integrate with a Google account, which is nice. Calendar entries, map placemarks, etc. are automatically shared between desktop and mobile. Gone is the need for the bug-ridden custom synchronisation software with which mobile phones of the past were plagued.

  Launching applications is mostly speedy, and recently used apps are kept loaded as long as memory needs allow. Although this garbage-collection-style of application management, where you are never quite sure whether an app is still running, takes a few moments of acclimatisation, it works reasonably well in day to day use. Most of the applications are well-behaved and save their data before terminating.

  Email

  Two email applications are included out of the box : one generic and one Gmail-only. As I do not use Gmail, I cannot comment on this application. The generic email client supports IMAP, but is rather limited in functionality. Fortunately, a much-enhanced version, K-9, is available for download. The main feature I find lacking here is threaded message view.

  The features, or lack thereof, in the email applications is not, however, of huge importance, as composing email, or any longer piece of text, is something one rather avoids on a system like this. The on-screen keyboard, while falling among the better of its kind, is still slow to use. Lack of tactile feedback means accidentally tapping the wrong key is easily done, and entering numbers or punctuation is an outright chore.

  Browser

  Whatever the Nexus lacks in email abilities, it makes up for with the browser. Surfing the web on a phone has never been this pleasant. Page rendering is quick, and zooming is fast and simple. Even pages not designed for mobile viewing are easy to read with smart reformatting almost entirely eliminating the sideways scrolling which hampered many a mobile browser of old.

  Calls and messaging

  Being a phone, the Nexus One is obviously able to make and receive calls, and it does so with ease. Entering a number or locating a stored contact are both straight-forward operations. During a call, audio is clear and of adequate loudness, although I have yet to use the phone in really noisy surroundings.

  The other traditional task of a mobile phone, messaging, is also well-supported. There isn’t really much to say about this.

  Multimedia

  Having a bit of an interest in most things multimedia, I obviously tested the capabilities of the Nexus by throwing some assorted samples at it, revealing ample space for improvement. With video limited to H.264 and MPEG4, and the only supported audio codecs being AAC, MP3, Vorbis, and AMR, there are many files which will not play.

  To make matters worse, only selected combinations of audio and video will play together. Several video files I tested played without sound, yet when presented with the very same audio data alone, it was correctly decoded. As for container formats, it appears restricted to MP4/MOV, and Ogg (for Vorbis). AVI files are recognised as media files, but I was unable to find an AVI file which would play.

  With a device clearly capable of so much more, the poor multimedia support is nothing short of embarrassing.

  The Market

  Much of the hype surrounding Android revolves around the Market, Google’s virtual marketplace for app authors to sell or give away their creations. The thousands of available applications are broadly categorised, and a search function is available.

  The categorised lists are divided into free and paid sections, while search results, disappointingly, are not. To aid the decision, ratings and comments are displayed alongside the summary and screenshots of each application. Overall, the process of finding and installing an application is mostly painless. While it could certainly be improved, it could also have been much worse.

  The applications themselves are, as hinted above, beyond numerous. Sadly, quality does not quite match up to quantity. The vast majority of the apps are pointless, though occasionally mildly amusing, gimmicks of no practical value. The really good ones, and they do exist, are very hard to find unless one knows precisely what to look for.

  Battery

  Packing great performance into a pocket-size device comes with a price in battery life. The battery in the Nexus lasts considerably shorter time than that in my older, less feature-packed Nokia phone. To some extent this is probably a result of me actually using it a lot more, yet the end result is the same : more frequent recharging. I should probably get used to the idea of recharging the phone every other night.

  Verdict

  The Nexus One is a capable hardware platform running an OS with plenty of potential. The applications are still somewhat lacking (or very hard to find), although the basic features work reasonably well. Hopefully future Android updates will see more and better core applications integrated, and I imagine that over time, I will find third-party apps to solve my problems in a way I like. I am not putting this phone on the shelf just yet.

• FFMPEG send RTP audio at 8k bytes/sec

  10 mai, par Muzza

  I'm trying to use FFMPEG to mimick a device that transmits G711U audio over UDP/RTP at 8k bytes per second.
The device im mimicking sends rtp packets every 20ms with 160byte payload.

  


  I've had limited success using the following command

  


  ffmpeg -f dshow -i audio="Microphone (Realtek(R) Audio)" -ac 1 -ar 8000 -ab 8 -acodec pcm_mulaw -f rtp rtp://127.0.0.1:12345?pkt_size=160


  


  This sends G711U encoded audio, in 160byte chunks, but streams at 64kB/s, not the 8kB/s that my device is expected, so the device errors out ?

  


  Any idea's would be massively appreciated !

  


  Thank you

  


  Log from FFMPEG

  


  >ffmpeg -f dshow -i audio="Microphone (Realtek(R) Audio)" -ac 1 -ar 8000 -ab 8 -acodec pcm_mulaw -f rtp rtp://127.0.0.1:12345?pkt_size=160
ffmpeg version 2025-04-23-git-25b0a8e295-essentials_build-www.gyan.dev Copyright (c) 2000-2025 the FFmpeg developers
  built with gcc 14.2.0 (Rev3, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma --enable-zlib --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-sdl2 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-libaom --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enable-libfreetype --enable-libfribidi --enable-libharfbuzz --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-dxva2 --enable-d3d11va --enable-d3d12va --enable-ffnvcodec --enable-libvpl --enable-nvdec --enable-nvenc --enable-vaapi --enable-libgme --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libtheora --enable-libvo-amrwbenc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-librubberband
  libavutil      60.  2.100 / 60.  2.100
  libavcodec     62.  0.101 / 62.  0.101
  libavformat    62.  0.100 / 62.  0.100
  libavdevice    62.  0.100 / 62.  0.100
  libavfilter    11.  0.100 / 11.  0.100
  libswscale      9.  0.100 /  9.  0.100
  libswresample   6.  0.100 /  6.  0.100
  libpostproc    59.  1.100 / 59.  1.100
[aist#0:0/pcm_s16le @ 00000198256b73c0] Guessed Channel Layout: stereo
Input #0, dshow, from 'audio=Microphone (Realtek(R) Audio)':
  Duration: N/A, start: 135470.702000, bitrate: 1411 kb/s
  Stream #0:0: Audio: pcm_s16le, 44100 Hz, stereo, s16, 1411 kb/s, Start-Time 135470.702s
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le (native) -> pcm_mulaw (native))
Press [q] to stop, [?] for help
[pcm_mulaw @ 00000198256cf240] Bitrate 8 is extremely low, maybe you mean 8k
Output #0, rtp, to 'rtp://127.0.0.1:12345?pkt_size=160':
  Metadata:
    encoder         : Lavf62.0.100
  Stream #0:0: Audio: pcm_mulaw, 8000 Hz, mono, s16 (8 bit), 64 kb/s
    Metadata:
      encoder         : Lavc62.0.101 pcm_mulaw
SDP:
v=0
o=- 0 0 IN IP4 127.0.0.1
s=No Name
c=IN IP4 127.0.0.1
t=0 0
a=tool:libavformat 62.0.100
m=audio 12345 RTP/AVP 0
b=AS:64

[out#0/rtp @ 00000198256cdd00] video:0KiB audio:973KiB subtitle:0KiB other streams:0KiB global headers:0KiB muxing overhead: 8.467470%
size=    1055KiB time=00:02:04.51 bitrate=  69.4kbits/s speed=   1x
Exiting normally, received signal 2.


  


  Wireshark :
Wireshark Log

  


  Shows packets being sent every 0.20ms