Книга: Embedded Linux Primer: A Practical, Real-World Approach

5.2.3. Architecture Setup

5.2.3. Architecture Setup

Among the first few things that happen in .../init/main.c in the start_kernel() function is the call to setup_arch(). This function takes a single parameter, a pointer to the kernel command line introduced earlier and detailed in the next section.

setup_arch(&command_line);

This statement calls an architecture-specific setup routine responsible for performing initialization tasks common across each major architecture. Among other functions, setup_arch() calls functions that identify the specific CPU and provides a mechanism for calling high-level CPU-specific initialization routines. One such function, called directly by setup_arch(), is setup_processor(), found in .../arch/arm/kernel/setup.c. This function verifies the CPU ID and revision, calls CPU-specific initialization functions, and displays several lines of information on the console during boot.

An example of this output can be found in Listing 5-3, lines 3 through 8. Here you can see the CPU type, ID string, and revision read directly from the processor core. This is followed by details of the processor cache type and size. In this example, the IXP425 has a 32KB I (instruction) cache and 32KB D (data) cache, along with other implementation details of the internal processor cache.

One of the final actions of the architecture setup routines is to perform any machine-dependent initialization. The exact mechanism for this varies across different architectures. For ARM, you will find machine-specific initialization in the .../arch/arm/mach-* series of directories, depending on your machine type. MIPS architecture also contains directories specific to supported reference platforms. For PowerPC, there is a machine-dependent structure that contains pointers to many common setup functions. We examine this in more detail in Chapter 16, "Porting Linux."

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