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> NAME="DEVAPI-SYNCHRONIZATION">Synchronization > >There are three levels of synchronization supported: > > > TYPE="1"
> > > 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
CLASS="FUNCTION"
>cyg_drv_isr_lock() > and
CLASS="FUNCTION"
>cyg_drv_isr_unlock() > functions. This
mechanism should be used sparingly and for short periods only.
For finer grained synchronization, individual spinlocks are also
supplied.
> > > > 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
CLASS="FUNCTION"
>cyg_drv_dsr_lock() > and
CLASS="FUNCTION"
>cyg_drv_dsr_unlock() > 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.
> > > > 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.
> > > >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,
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>even in ISRs > >. 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. > > CLASS="NAVFOOTER"
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