The boot process

The WMA11b has a rather convoluted boot process. The bootloader, kernel and an initial ramdisk are stored in flash memory on board the device. The media streaming software, however, is stored in a cramfs filesystem image on the server PC and must be downloaded to the device to complete the booting process.

  1. The boot loader initialises the hardware, including performing memory tests. It then decompresses the kernel and initial ramdisk into RAM.
  2. The bootloader jumps to the start address of the kernel, which decompresses itself, initialises then executes the script linuxrc as the init process. This script initialises the system and brings up a network interface. Ethernet is tried first, and if this fails the device falls back to wireless.
  3. Snip lots of boring details...
  4. The /apploader/apploader program multicasts SSDP advertisments every 5 seconds. It advertises itself as a urn:schemas-upnp-org:device:AppLoaderClient:1 device with two services ApplicationTransferService:1 and AdapterInfoService:1. These are interesting because they reference upnp.org but don't appear to be official upnp.org standards. If you know anything about this device or have a specification I'd like to hear from you.
  5. The server PC will be listening for this device and tells the device where to fetch the cramfs filesystem image by invoking the SetApplicationPackageURI action.
  6. The WMA11b opens a TCP connection to a port on the server PC which immediately sends the image then closes the connection. For this transfer no HTTP, FTP or any other protocol is used.
  7. The image is saved in /tmp then mounted via a loopback device at /guava.
  8. The binary mrdDevice creates a urn:schemas-upnp-org:device:MediaRenderer:1 device with three services RendererControl:1, ConnectionManager:1 and AVTransport:1
  9. The binary rio creates a urn:schemas-upnp-org:device:RemoteIO:1 device with two services RemoteIO:1 and RemoteInput:1.

If you are interested in investigating the uPnP interface to the WMA11b I recommend you check out the Intel uPnP tools.

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By Andrew Wild | Visitor Statistics | Portugal Holiday
This file last modified 28/09/2004 01:17am