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100 lines
4.2 KiB
Plaintext
100 lines
4.2 KiB
Plaintext
sys_arch interface for lwIP
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Author: Adam Dunkels
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Simon Goldschmidt
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The operating system emulation layer provides a common interface
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between the lwIP code and the underlying operating system kernel. The
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general idea is that porting lwIP to new architectures requires only
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small changes to a few header files and a new sys_arch
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implementation. It is also possible to do a sys_arch implementation
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that does not rely on any underlying operating system.
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The sys_arch provides semaphores, mailboxes and mutexes to lwIP. For the full
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lwIP functionality, multiple threads support can be implemented in the
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sys_arch, but this is not required for the basic lwIP
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functionality. Timer scheduling is implemented in lwIP, but can be implemented
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by the sys_arch port (LWIP_TIMERS_CUSTOM==1).
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In addition to the source file providing the functionality of sys_arch,
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the OS emulation layer must provide several header files defining
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macros used throughout lwip. The files required and the macros they
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must define are listed below the sys_arch description.
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Semaphores can be either counting or binary - lwIP works with both
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kinds. Mailboxes should be implemented as a queue which allows multiple messages
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to be posted (implementing as a rendez-vous point where only one message can be
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posted at a time can have a highly negative impact on performance). A message
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in a mailbox is just a pointer, nothing more.
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Semaphores are represented by the type "sys_sem_t" which is typedef'd
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in the sys_arch.h file. Mailboxes are equivalently represented by the
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type "sys_mbox_t". Mutexes are represented by the type "sys_mutex_t".
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lwIP does not place any restrictions on how these types are represented
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internally.
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Since lwIP 1.4.0, semaphore, mutexes and mailbox functions are prototyped in a way that
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allows both using pointers or actual OS structures to be used. This way, memory
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required for such types can be either allocated in place (globally or on the
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stack) or on the heap (allocated internally in the "*_new()" functions).
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Note:
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Be careful with using mem_malloc() in sys_arch. When malloc() refers to
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mem_malloc() you can run into a circular function call problem. In mem.c
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mem_init() tries to allcate a semaphore using mem_malloc, which of course
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can't be performed when sys_arch uses mem_malloc.
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-------------------------------------------------------------------------------
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Additional files required for the "OS support" emulation layer:
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-------------------------------------------------------------------------------
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cc.h - Architecture environment, some compiler specific, some
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environment specific (probably should move env stuff
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to sys_arch.h.)
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Typedefs for the types used by lwip -
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u8_t, s8_t, u16_t, s16_t, u32_t, s32_t, mem_ptr_t
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Compiler hints for packing lwip's structures -
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PACK_STRUCT_FIELD(x)
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PACK_STRUCT_STRUCT
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PACK_STRUCT_BEGIN
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PACK_STRUCT_END
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Platform specific diagnostic output -
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LWIP_PLATFORM_DIAG(x) - non-fatal, print a message.
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LWIP_PLATFORM_ASSERT(x) - fatal, print message and abandon execution.
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Portability defines for printf formatters:
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U16_F, S16_F, X16_F, U32_F, S32_F, X32_F, SZT_F
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"lightweight" synchronization mechanisms -
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SYS_ARCH_DECL_PROTECT(x) - declare a protection state variable.
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SYS_ARCH_PROTECT(x) - enter protection mode.
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SYS_ARCH_UNPROTECT(x) - leave protection mode.
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If the compiler does not provide memset() this file must include a
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definition of it, or include a file which defines it.
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This file must either include a system-local <errno.h> which defines
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the standard *nix error codes (or define LWIP_ERRNO_INCLUDE to that file name),
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or it should #define LWIP_PROVIDE_ERRNO to make lwip/arch.h define the codes
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which are used throughout.
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perf.h - Architecture specific performance measurement.
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Measurement calls made throughout lwip, these can be defined to nothing.
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PERF_START - start measuring something.
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PERF_STOP(x) - stop measuring something, and record the result.
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sys_arch.h - Tied to sys_arch.c
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Arch dependent types for the following objects:
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sys_sem_t, sys_mbox_t, sys_thread_t,
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And, optionally:
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sys_prot_t
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Defines to set vars of sys_mbox_t and sys_sem_t to NULL.
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SYS_MBOX_NULL NULL
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SYS_SEM_NULL NULL
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