Intel 80310 I/O Processor Chipset AAU Coding Techniques

Intel ® 80310 I/O Processor Chipset AAU Coding TechniquesLow-Level Design DocumentThe AAU descriptor data structure is filled out by the user. It maps over the first portion of the softwaredescriptor sw_aau_t data structure. Casting eliminates a copy of values from one data structure toanother. When the user passes a correct user SGL list, all the API has to do is re-cast the list intosoftware descriptors and feed it to the processing queue. This requires a slight bit more knowledge of theAAU fields on the users part, but improves performance of the AAU operation considerably.Table 10.AAU User SGL Structurestruct_aau_sgl_t{aau_desc_taau_desc;u32status;struct_aau_sgl_t *next_sgl; /* Pointer to next SG */void*dest;void *src[4] ; /* Source group 1 */void *src_ext[4]; /* Source group 2 */u32 total_src; /* Total number of sources passed down */} aau_sgl_t;3.1.5 Data PathThe following is required for an application to utilize the AAU hardware through the AAU API. Theapplication must first attempt to request the usage of the AAU by calling the aau_request()function. This function requests and registers an interrupt for the AAU. When successful, theapplication is allowed to use the AAU. The API also keeps track of the usage of the AAU by using areference count method. When unsuccessful the error –EBUSY is returned to the caller.The driver applications are required to create a scattered gather list (SGL) defined in the format ofaau_sgl_t format with all information for AAU operation completed. The driver application isresponsible for allocating and keeping track of the memory to store the AAU input data and result. Theapplication calls the aau_queue_buffer() function to pass down the user SGL. The AAU APIgenerates an AAU descriptor chain from the passed down SGL using the AAU software descriptorsfrom the free AAU resource stack. When no free software descriptors are available the API goes to sleepfor a short period of time, and then tries again ten times before giving up and returning –ENOMEMerror. The Interrupt Enable bit is set by the function in the DC field of the last hardware descriptor in thechain to indicate end of chain. The AAU chain is queued into the processing queue by the functionwhich then calls aau_start() for the application. The aau_start() function checks to determineif the AAU is active. If not active then this is a new operation and which requires setting the appropriatebits, links accordingly and starting the AAU. If active then it is an ongoing operation which requiresappending to the existing chain and setting the chain resume bit. At this point theaau_queue_buffer()returns the control to the application while the AAU is doing its work.The application has two choices in handling the result of AAU completion:1. Sleep on the AAUs wait queue until being notified by the bottom half interrupt handler later onwhen operation is complete2. Continue and be notified by a callback function when the operation on the chain is completevia the SGL passed down.The AAU meanwhile processes the chain and triggers an interrupt when it encounters the InterruptEnable Bit being set in a descriptor being processed or an error condition is encountered.White Paper 15