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+><TITLE
+>Synchronization Levels</TITLE
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+WIDTH="80%"
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+>Chapter 18. Device Driver Interface to the Kernel</TD
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+><DIV
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+><H1
+CLASS="SECTION"
+><A
+NAME="DEVAPI-SYNCHRONIZATION-LEVELS">Synchronization Levels</H1
+><P
+>Since it would be dangerous for an ISR or DSR to make a call
+that might reschedule the current thread (by trying to lock a mutex
+for example) all functions in this API have an associated synchronization
+level. These levels are:</P
+><P
+></P
+><DIV
+CLASS="VARIABLELIST"
+><DL
+><DT
+>Thread</DT
+><DD
+><P
+> This function may only be called from within threads. This is
+ usually the client code that makes calls into the device driver.
+ In a non-kernel configuration, this will be code running at the
+ default non-interrupt level.
+ </P
+></DD
+><DT
+>DSR</DT
+><DD
+><P
+> This function may be called by either DSR or thread code.
+ </P
+></DD
+><DT
+>ISR</DT
+><DD
+><P
+> This function may be called from ISR, DSR or thread code.
+ </P
+></DD
+></DL
+></DIV
+><P
+>The following table shows, for each API function, the levels
+at which is may be called:</P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+> Callable from:
+Function ISR DSR Thread
+-------------------------------------------------------------------------
+
+cyg_drv_isr_lock X X X
+cyg_drv_isr_unlock X X X
+cyg_drv_spinlock_init X
+cyg_drv_spinlock_destroy X
+cyg_drv_spinlock_spin X X X
+cyg_drv_spinlock_clear X X X
+cyg_drv_spinlock_try X X X
+cyg_drv_spinlock_test X X X
+cyg_drv_spinlock_spin_intsave X X X
+cyg_drv_spinlock_clear_intsave X X X
+cyg_drv_dsr_lock X X
+cyg_drv_dsr_unlock X X
+cyg_drv_mutex_init X
+cyg_drv_mutex_destroy X
+cyg_drv_mutex_lock X
+cyg_drv_mutex_trylock X
+cyg_drv_mutex_unlock X
+cyg_drv_mutex_release X
+cyg_drv_cond_init X
+cyg_drv_cond_destroy X
+cyg_drv_cond_wait X
+cyg_drv_cond_signal X X
+cyg_drv_cond_broadcast X X
+cyg_drv_interrupt_create X
+cyg_drv_interrupt_delete X
+cyg_drv_interrupt_attach X X X
+cyg_drv_interrupt_detach X X X
+cyg_drv_interrupt_mask X X X
+cyg_drv_interrupt_unmask X X X
+cyg_drv_interrupt_acknowledge X X X
+cyg_drv_interrupt_configure X X X
+cyg_drv_interrupt_level X X X
+cyg_drv_interrupt_set_cpu X X X
+cyg_drv_interrupt_get_cpu X X X </PRE
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