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Elaborate RTEMS libbsd initialization
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Sebastian Huber
parent
a3d2498e49
commit
8a4f070701
137
libbsd.txt
137
libbsd.txt
@ -261,20 +261,135 @@ Generating into /home/joel/newbsd/git/libbsd-8.2
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The script may also be used to generate a diff in either forward or reverse
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direction.
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== Initialization of RTEMS Libbsd
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== Initialization of RTEMS libbsd
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The initialization of the RTEMS Libbsd is based on the FreeBSD SYSINIT
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infrastructure. This is simply because we are initializing a subset of
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FreeBSD. For details refer to http://www.freebsd.org/cgi/man.cgi?query=SYSINIT&sektion=9&apropos=0&manpath=FreeBSD+9-current
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The initialization of the RTEMS libbsd is based on the FreeBSD SYSINIT(9)
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infrastructure. The key to initializing a system is to ensure that the desired
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device drivers are explicitly pulled into the linked application. This plus
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linking against the libbsd library will pull in the necessary FreeBSD
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infrastructure.
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The key to initializing a system is to ensure that the desired device
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drivers are explicitly pulled into the linked application. This plus
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linking against the Libsd library will pull in the necessary FreeBSD
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infrastructure. The SYSINIT structures are automatically built at link
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time and the various initialization routines will thus be executed in'
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the correct order.
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The FreeBSD kernel is not a library like the RTEMS kernel. It is a bunch of
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object files linked together. If we have a library, then creating the
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executable is simple. We begin with a start symbol and recursively resolve all
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references. With a bunch of object files linked together we need a different
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mechanism. Most object files don't know each other. Lets say we have a driver
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module. The rest of the system has no references to this driver module. The
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driver module needs a way to tell the rest of the system: Hey, kernel I am
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here, please use my services!
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XXX This needs more details.
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This registration of independent components is performed by SYSINIT(9) and
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specializations:
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http://www.freebsd.org/cgi/man.cgi?query=SYSINIT
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The SYSINIT(9) uses some global data structures that are placed in a certain
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section. In the linker command file we need this:
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[listing]
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----
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.robsdsets : {
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_bsd__start_set_modmetadata_set = .;
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*(_bsd_set_modmetadata_set);
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_bsd__stop_set_modmetadata_set = .;
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_bsd__start_set_sysctl_set = .;
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*(_bsd_set_sysctl_set);
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_bsd__stop_set_sysctl_set = .;
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} > REGION_RODATA AT > REGION_RODATA_LOAD
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.rwbsdsets : {
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_bsd__start_set_sysinit_set = .;
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*(_bsd_set_sysinit_set);
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_bsd__stop_set_sysinit_set = .;
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} > REGION_DATA AT > REGION_DATA_LOAD
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----
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Here you can see, that these global data structures are collected into
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continuous memory areas. This memory area can be identified by start and stop
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symbols. This constructs a table of uniform items.
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The low level FreeBSD code calls at some time during the initialization the
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mi_startup() function (machine independent startup). This function will sort
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the SYSINIT(9) set and call handler functions which perform further
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initialization. The last step is the scheduler invocation.
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The SYSINIT(9) routines are run in mi_startup() which is called by
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rtems_bsd_initialize().
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This is also explained in "The Design and Implementation of the FreeBSD
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Operating System" section 14.3 "Kernel Initialization".
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In RTEMS we have a library and not a bunch of object files. Thus we need a way
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to pull-in the desired services out of the libbsd. Here the
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"rtems-bsd-sysinit.h" comes into play. The SYSINIT(9) macros have been
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modified and extended for RTEMS in "sys/kernel.h":
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[listing]
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----
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#ifndef __rtems__
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#define C_SYSINIT(uniquifier, subsystem, order, func, ident) \
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static struct sysinit uniquifier ## _sys_init = { \
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subsystem, \
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order, \
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func, \
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(ident) \
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}; \
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DATA_SET(sysinit_set,uniquifier ## _sys_init)
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#else /* __rtems__ */
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#define SYSINIT_ENTRY_NAME(uniquifier) \
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_bsd_ ## uniquifier ## _sys_init
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#define SYSINIT_REFERENCE_NAME(uniquifier) \
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_bsd_ ## uniquifier ## _sys_init_ref
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#define C_SYSINIT(uniquifier, subsystem, order, func, ident) \
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struct sysinit SYSINIT_ENTRY_NAME(uniquifier) = { \
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subsystem, \
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order, \
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func, \
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(ident) \
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}; \
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DATA_SET(sysinit_set,SYSINIT_ENTRY_NAME(uniquifier))
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#define SYSINIT_REFERENCE(uniquifier) \
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extern struct sysinit SYSINIT_ENTRY_NAME(uniquifier); \
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static struct sysinit const * const \
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SYSINIT_REFERENCE_NAME(uniquifier) __used \
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= &SYSINIT_ENTRY_NAME(uniquifier)
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#define SYSINIT_MODULE_REFERENCE(mod) \
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SYSINIT_REFERENCE(mod ## module)
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#define SYSINIT_DRIVER_REFERENCE(driver, bus) \
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SYSINIT_MODULE_REFERENCE(driver ## _ ## bus)
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#endif /* __rtems__ */
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----
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Here you see that the SYSINIT(9) entries are no longer static. The
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*_REFERENCE() macros will create references to the corresponding modules which
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are later resolved by the linker. The application has to provide an object
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file with references to all required FreeBSD modules.
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The FreeBSD device model is quite elaborated (with follow-ups):
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http://www.freebsd.org/cgi/man.cgi?query=driver
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The devices form a tree with the Nexus device at a high-level. This Nexus
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device is architecture specific in FreeBSD. In RTEMS we have our own Nexus
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device, see "rtems-bsd-nexus.c". It uses a table to add child devices:
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[listing]
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----
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const char *const _bsd_nexus_devices [] = {
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#ifdef NEED_USB_OHCI
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"ohci",
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#endif
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#ifdef NEED_USB_EHCI
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"ehci",
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#endif
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#ifdef NEED_SDHC
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"sdhci",
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#endif
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NULL
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};
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----
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This table must be provided by the application.
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=== SYSCTL_NODE Example
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