Hi Sheng,

Hi all, Does anybody know whether there are some documents in English for teaching how to drive a audio card such that a application on l4 can use it? It is known that driver can be ported via DDE but how to do that? I am a newbie in this area, Could you please give me some advice?

Generally, the approach to get any driver running with the DDE works as follows (note, when I speak of DDE examples, I mean the ones in l4/pkg/dde as well as larger examples such as l4/pkg/ore): 1) Start a new L4 application consisting of a main() function calling the DDE initialization routines. There are several ones depending on which DDE subsystems you want to use (timers, memory, pci, ...). Please consult the DDE examples for that. 2) After calling the init functions, call l4dde26_do_initcalls(). This will execute all the functions Linux functions marked as *_initcall(), such as the init function of your driver. 3) Compile your application (consisting of your main function and the driver you want to use) and link it with the DDE libraries as you can see from the DDE examples. 4) If your type of device is already supported by the DDE (such as network, block and TPM devices), then this should give you a working executable which you then just boot and there goes your driver. Proceed to step 6 in this case. 5) If your type of device is not yet supported, which will be the case for sound devices, then you will encounter potentially lots of linker errors in step 3. In this case * Find out whether the missing function is necessary. If you can get away without it, then implement it as an empty function returning a default good value. * If the function does something necessary: * Check if you can reuse the implementation from the Linux kernel. This is the case for functions that use default Linux features that are provided by the DDE, such as kmalloc(), request_region() etc. * In some cases reusing things from Linux will result in too much unnecessary Linux code ending up in your application or it might prove too hard to get all of it compile. If this occurs, consider reimplementing the feature to the extent needed by your application. Note, that step 5) is the real hard part and it often takes a lot of time to understand which code you can copy from Linux and which one you should replace with code written by yourself. If everything compiles, proceed to step 6. 6) If the Linux part of your driver compiles and starting the application boots and initializes the driver, it is time to add some L4 glue code, so that external applications can use your driver. 7) Have fun with your driver server. After gaining some experience with extending DDE, you will be able to identify which pieces of your newly written code are only needed for your specific application and which ones should be provided for future device drivers, too. The latter should then be incorporated into a DDE subsystem (e.g., a library in the DDE package), but I recommend, you don't worry about this at the current point. Bjoern