Semaphores - Analog Devices ADSP-BF535 Blackfin Hardware Reference Manual

Semaphores

The ADSP-BF535 processor supports nested and non-nested interrupts,
as well as self-nested interrupts. For explanations of the various modes of
servicing events, see
page 4-48.
Semaphores
Semaphores provide a mechanism for communication between multiple
processors or processes/threads running in the same system. They are used
to coordinate resource sharing. For instance, if a process is using a particu-
lar resource and another process requires that same resource, it must wait
until the first process signals that it is no longer using the resource. This
signaling is accomplished via semaphores.
Semaphore coherency is guaranteed by using the Test and Set Byte
(Atomic) instruction (
functions.
• Loads the byte at memory location pointed to by a P-register.
• Sets
CC
• Stores the value back in its original location (but with the most sig-
nificant bit set to 1).
The events triggered by
memory where the address is located is acquired and not relinquished
until the store operation completes. In multithreaded systems, the
instruction is required to maintain semaphore consistency.
TESTSET
To ensure that the store operation is flushed through any store or write
buffers, issue an
19-6
"Interrupts With and Without Nesting" on
). The
TESTSET
if the value is equal to zero.
TESTSET
immediately after semaphore release.
SSYNC
ADSP-BF535 Blackfin Processor Hardware Reference
instruction performs these
TESTSET
are atomic operations. The bus for the