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>Synchronization</A
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><P
>There are three levels of synchronization supported:</P
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> Synchronization with ISRs. This normally means disabling
interrupts to prevent the ISR running during a critical
section. In an SMP environment, this will also require the use of
a spinlock to synchronize with ISRs, DSRs or threads running on
other CPUs. This is implemented by the
<CODE
CLASS="FUNCTION"
>cyg_drv_isr_lock()</CODE
> and
<CODE
CLASS="FUNCTION"
>cyg_drv_isr_unlock()</CODE
> functions. This
mechanism should be used sparingly and for short periods only.
For finer grained synchronization, individual spinlocks are also
supplied.
</P
></LI
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><P
> Synchronization with DSRs. This will be implemented in the kernel
by taking the scheduler lock to prevent DSRs running during
critical sections. In non-kernel configurations it will be
implemented by non-kernel code. This is implemented by the
<CODE
CLASS="FUNCTION"
>cyg_drv_dsr_lock()</CODE
> and
<CODE
CLASS="FUNCTION"
>cyg_drv_dsr_unlock()</CODE
> functions. As with ISR
synchronization, this mechanism should be used sparingly. Only
DSRs and threads may use this synchronization mechanism, ISRs are
not allowed to do this.
</P
></LI
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><P
> Synchronization with threads. This is implemented with mutexes
and condition variables. Only threads may lock the mutexes and
wait on the condition variables, although DSRs may signal
condition variables.
</P
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>Any data that is accessed from more than one level must be protected
against concurrent access. Data that is accessed by ISRs must be
protected with the ISR lock, or a spinlock at all times,
<SPAN
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><I
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>even in ISRs</I
></SPAN
>. Data that is shared between DSRs
and threads should be protected with the DSR lock. Data that is only
accessed by threads must be protected with mutexes.</P
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