Visible to Intel only — GUID: iga1443129789664
Ixiasoft
Visible to Intel only — GUID: iga1443129789664
Ixiasoft
31.7.1.3.2. Descriptor Processing
The DMA descriptors specify data transfers to be performed. With the Prefetcher core, a descriptor is stored in memory and accessed by the Prefetcher core through its descriptor write and descriptor read Avalon® -MM host. The mSGDMA has an internal FIFO to store descriptors read from memory. This FIFO is located in the dispatcher’s core. The descriptors must be initialized and aligned on a descriptor read/write data width boundary. The Prefetcher core relies on a cleared Owned By Hardware bit to stop processing. When the Owedn by Hardware bit is 1, the Prefetcher core goes ahead to process the descriptor. When the Owned by Hardware bit is 0, the Prefetcher core does not process the current descriptor and assumes the linked list has ended or the next descriptor linked list is not yet ready.
Each time a descriptor has been processed, the core updates the Actual Byte Transferred, Status and Control fields of the descriptor in memory (descriptor write back). The Owned by Hardware bit in the descriptor control field is cleared by the core during descriptor write back. Refer to software programming model section to know more about recommended way to set up the Prefetcher core, building and updating the descriptor list.
In order for the Prefetcher to know which memory addresses to perform descriptor write back, the next descriptor pointer information will need to be buffered in Prefetcher core. This buffer depth will be similar to descriptor FIFO depth in dispatcher core. This information is taken out from buffer each time a response is received from dispatcher.