Intel IXP1200 manual Mutex Vectors, Mutexvectorinit, Mutexvectorenter, Mutexvectorexit

IXP1200 Network Processor Family ATM OC-3/12/Ethernet IP Router Example Design

// sram[read, $foo], ordered, ctx_swap

4.10Mutex Vectors

Mutex vectors are an extension to critical sections that allows multiple critical sections to be contained within a single absolute register. (critsect.uc implements critical sections, critsect macros are documented in the IXP1200 Macro Library Reference Manual.) Critsect macros are used to allow only 1 of the 4 threads of a microengine to execute a critical code section at one time. The critsect macros allow the four threads within a microengine to use a semaphore implemented in an absolute register. The semaphore is used to restrict use of a resource shared by the threads in a microengine. The OC-3 Ethernet receiver uses them to prevent multiple threads from enqueuing on the same transmit queue, while allowing them to concurrently enqueue on different transmit queues. The mutex vector subsystem is implemented in mutex_vector.uc.

The following critical section macros are for use within a microengine. Up to 32 critical sections can be implemented with each absolute register. These macros are used where run-time selection between multiple mutexes is necessary. If only one mutex is needed, the macros in critsect.uc are slightly smaller and faster.

4.10.1mutex_vector_init()

Initializes critical sections to enable subsequent mutex_vector_enter() to succeed.

mutex_vector_init(out_abs_reg)

Parameter	Description
out_abs_reg	Absolute register containing the semaphores.

4.10.2mutex_vector_enter()

Enters the specified microengine critical section.

mutex_vector_enter(io_abs_reg, in_bit_number)

Parameter	Description
out_abs_reg	Absolute register containing the semaphores.
	bit number of the semaphore
in_bit_number	0 bits: critical section available
	1 bits: critical section occupied
	init: clears all bits

4.10.3mutex_vector_exit()

Exits the specified microengine critical section.

mutex_vector_exit(io_abs_reg, in_bit_number)

Application Note 53

Modified on: 3/20/02,