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-NAME="DEVAPI-SMP-SUPPORT">SMP Support</H1
-><P
->Some eCos targets contain support for Symmetric Multi-Processing (SMP)
-configurations, where more than one CPU may be present. This option
-has a number of ramifications for the way in which device drivers must
-be written if they are to be SMP-compatible. </P
-><P
->Since it is possible for the ISR, DSR and thread components of a
-device driver to execute on different CPUs, it is important that
-SMP-compatible device drivers use the driver API routines correctly.</P
-><P
->Synchronization between threads and DSRs continues to require that the
-thread-side code use <TT
-CLASS="FUNCTION"
->cyg_drv_dsr_lock()</TT
-> and
-<TT
-CLASS="FUNCTION"
->cyg_drv_dsr_unlock()</TT
-> to protect access to shared
-data. While it is not strictly necessary for DSR code to claim the DSR
-lock, since DSRs are run with it claimed already, it is good practice
-to do so.</P
-><P
->Synchronization between ISRs and DSRs or threads requires that access
-to sensitive data be protected, in all places, by calls to
-<TT
-CLASS="FUNCTION"
->cyg_drv_isr_lock()</TT
-> and
-<TT
-CLASS="FUNCTION"
->cyg_drv_isr_unlock()</TT
->. Disabling or masking
-interrupts is not adequate, since the thread or DSR may be running on
-a different CPU and interrupt enable/disable only work on the current
-CPU.</P
-><P
->The ISR lock, for SMP systems, not only disables local interrupts, but
-also acquires a spinlock to protect against concurrent access from
-other CPUs. This is necessary because ISRs are not run with the
-scheduler lock claimed. Hence they can run in parallel with the other
-components of the device driver.</P
-><P
->The ISR lock provided by the driver API is just a shared spinlock that
-is available for use by all drivers. If a driver needs to implement a
-finer grain of locking, it can use private spinlocks, accessed via the
-<TT
-CLASS="FUNCTION"
->cyg_drv_spinlock_*()</TT
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