Re: [ECOS] ecos kernel modification and kapidata

[Andrew Lunn <andrew@lunn.ch>]

On Fri, Sep 07, 2007 at 02:49:41PM +1000, Yi Tang wrote:
> Hi,
>
> I'm currently doing some modification to ecos kernel, mainly trying to add 
> a custom scheduler. I have created my own scheduler implementation file and 
> changed some to kapi.cxx (hxx).
>
> I thought that's all. After finished the cdl modification to add the new 
> scheduler, I tried to build the library. But during the compiling, it says 
> I also need to do some modification to kapidata.hxx.

Could you be more specific about this....

> The thing is I don't understand the role this file takes in the whole 
> kernel. 

There is a nice comment in kapidata.h

Description: This file defines the structures used in the native API. The
//              sizes of these structures are dependent on the system
//              configuration and must be kept in step with their real
//              counterparts in the C++ headers.
//              IMPORTANT: It is NOT guaranteed that the fields of these
//              structures correspond to the equivalent fields in the
//              C++ classes they shadow.
//
//              One oddity with this file is that the way many of the "mirror"
//              classes are defined with macros. The resulting structures
//              then have a "flat" layout, rather than just declaring a
//              member structure directly in the structure. The reason for
//              this is that as of GCC 3.x, the C++ compiler will optimise
//              classes by removing padding and reusing it for subsequent
//              members defined in a derived class. This affects some targets
//              (including PowerPC and MIPS at least) when a C++ base class
//              includes a long long. By instead arranging for the C structure
//              to just list all the members directly, the compiler will then
//              behave the same for the C structures as the C++ classes.
//
//              This means that care has to be taken to follow the same
//              methodology if new stuff is added to this file. Even if
//              it doesn't contain long longs for your target, it may for
//              others, depending on HAL definitions.
//

The memory for kernel data structures, like threads, mutexes, flags
etc are allocated in applications C code. However these structures are
actually used as classes in the C++ code. You need to ensure that the
C structure is the same size as the C++ class. If not, bad things will
happen. If you have added members to a class, you also need to add
extra members to the C structures. Otherwise too little memory will be
allocated.


> Also is there any other source file I need to modify?

Hard to say. It sounds like you have made major changes to the API, so
without seeing your code it is impossible to say.

        Andrew

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