Internal Communication and Semaphores
MSC8113 Reference Manual, Rev. 0
Freescale Semiconductor
1-27
1.3.2 Atomic Operations
When the SC140 core executes the
bmtset
instruction, it issues a read access followed by a write
access to the semaphore address and then asserts the atomic signal. The MQBus and the SQBus
prevent the SC140 cores from writing to the same semaphore address. A semaphore shared by an
SC140 core and an external host on the system bus is protected by a snooper on the bus interface.
When the system bus interface receives a read with atomic signal, the snooper starts to snoop the
bus. The snooper returns a failure if the external host writes to the same location. Snoopers also
protect the M1 and the M2 memories, which are accessible to both the SC140 cores and external
hosts.
Note:
For details, see Section 9.3, Extended QBus System.
1.3.3 Hardware Semaphores
There are eight coded hardware semaphores. Each semaphore is an 8-bit register with a selective
write protection mechanism. When the register value is zero, it is writable to any new value.
When the register value is not zero, it is writable only to zero. Each SC140 core/host/task has a
unique pre-defined lock number (8-bit code). When trying to lock the semaphore, the SC140 core
writes its lock number to the semaphore and then reads it. If the read value equals its lock
number, the semaphore belongs to that host and is essentially locked. An SC140 core/host/task
releases the semaphore by simply writing 0.
Note:
For details, see Chapter 15, Hardware Semaphores.
Содержание MSC8113
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