2.15 WD_DMASyncCpu

2.15 WD_DMASyncCpu
	Chapter 2. WD_xxx PCI/PCMCIA/ISA Functions

Purpose

• Synchronizes the cache of all CPUs with the DMA buffer, by flushing the data from the CPU caches.


	This function should be called before performing a DMA transfer (see Remarks below).

Prototype

DWORD WD_DMASyncCpu(
    HANDLE hWD,
    WD_DMA *pDMA);

Parameters

Name	Type	Input/Output
hWD	HANDLE	Input
pDMA	WD_DMA*	Input

Description

Name	Description
hWD	Handle to WinDriver's kernel-mode driver as received from `WD_Open`() [5.2]
pDMA	Pointer to a DMA information structure, received from a previous call to `WD_DMALock`() [2.13]

Return Value

Returns WD_STATUS_SUCCESS (0) on success, or an appropriate error code otherwise [A].

Remarks

An asynchronous DMA read or write operation accesses data in memory, not in the processor (CPU) cache, which resides between the CPU and the host's physical memory. Unless the CPU cache has been flushed, by calling WD_DMASyncCpu(), just before a read transfer, the data transferred into system memory by the DMA operation could be overwritten with stale data if the CPU cache is flushed later. Unless the CPU cache has been flushed by calling WD_DMASyncCpu() just before a write transfer, the data in the CPU cache might be more up-to-date than the copy in memory.

Example

WD_DMASyncCpu(hWD, &dma);


2.14 WD_DMAUnlock		2.16 WD_DMASyncIo