Intel 80310 I/O Processor Chipset AAU Coding Techniques

Intel ® 80310 I/O Processor Chipset AAU Coding TechniquesLow-Level Design DocumentWhen an AAU interrupt is asserted, the interrupt handler function aau_irq_handler() iscalled. Clearing an interrupt requires clearing it at the source. In this case the source is theAccelerator Status Register. When the Accelerator Status Resister has been cleared in the interrupthandler, the interrupt assert bit shall be cleared by the hardware as a consequence. As long as theAAU interrupt is asserted due to new AAU interrupts, the interrupt handler continues to remove thedescriptors from the channel process queue and put the descriptors in the channel holding queueuntil the ADAR value equals to the address of the descriptor or the queue is empty. When theADAR equals the descriptor address and the ASR indicates that the channel is active then thatdescriptor is not removed. Once the interrupt handler no longer sees an AAU interrupt beingasserted it schedules a bottom half handler in the immediate task queue to process the holdingqueue and notify the application of the progress of the AAU operation.The application calls the function aau_free() when it no longer needs the AAU and wants torelease it. Depending on the reference count, the IRQ requested for the AAU may be freed. Whenthere are any errors for the AAU unit, the AAU registers are cleared, all resources are returned, andthe reference count shall be reset to 0.Figure 2 shows the state trace diagram for a normal operation of the AAU. The diagramdemonstrates all the necessary function calls that are performed during a normal, simple AAUexecution path. The section explaining the APIs in detail follows.Figure 2.AAU State Trace DiagramUser AAU INTC Systemaau_get_buffer()aau_init()aau_queue_buffer()aau_start()AAU Completeaau_irq_handler()Sleep on wait queue or Proceed oncallbackaau_process()aau_buffer_return()Callback or Wake if Sleepingaau_free()aau_task()16 White Paper