PRD (physical region descriptor) pre-fetch methods for DMA (direct memory access) units

摘要

PRD (Physical Region Descriptor) pre-fetch methods for DMA (Direct Memory Access) unit are provided. When a DMA out transaction for a memory is performed, it is determined whether a first queue is full or nearly full, wherein the first queue is used to store data corresponding to the DMA out transaction. If the first queue is full or nearly full, at least one PRD entry is read from a first PRD table, and stored to a first cache. When a DMA in transaction for the memory is performed, it is determined whether a second queue is empty or nearly empty, wherein the second queue is used to store data corresponding to the DMA in transaction. If the second queue is empty or nearly empty, at least one PRD entry is read from a second PRD table, and stored to a second cache.

主权项

1. A Physical Region Descriptor (PRD) pre-fetch method for a Direct Memory Access (DMA) unit, comprising:
determining whether a DMA request comprises a DMA out request or a DMA in request; monitoring a queue by detecting a data storage state of the queue to determine whether to pre-fetch a PRD entry when the DMA request is received, wherein the queue is used to store data corresponding to the DMA request; when the queue is full and cannot hold any more data from a memory for the DMA out request or the queue is empty and cannot give any more data to the memory for the DMA in request, pre-fetching at least one PRD entry from a PRD table and storing the PRD entry to a cache memory; and once the queue is not full for the DMA out request or the queue is not empty for the DMA in request, stopping pre-fetching the PRD entry from the PRD table; and reading a current PRD entry from the cache memory and performing a DMA out transaction according to the current PRD entry once the queue is not full for the DMA out request, or performing a DMA in transaction according to the current PRD entry once the queue is not empty for the DMA in request.