d_slave Kernel Service

Purpose

Initializes a block-mode direct memory access (DMA) transfer for a DMA slave.

Syntax

#include <sys/types.h>
#include <sys/errno.h>
#include <sys/dma.h>
#include <sys/xmem.h>

void d_slave 
(channel_id, flags, baddr, 
count, dp)
int channel_id;
int flags;
caddr_t baddr;
size_t count;
struct xmem *dp;

Parameters

Description

The d_slave kernel service sets up the DMA channel specified by the channel_id parameter to perform a block-mode DMA transfer for a DMA slave. The flags parameter controls the operation of the d_slave service. "Understanding Direct Memory Access (DMA)" in AIX Kernel Extensions and Device Support Programming Concepts describes DMA slaves and masters.

The d_slave service does not initiate the DMA transfer. The device initiates all DMA memory references. The d_slave service sets up the system address-generation hardware to indicate the specified buffer.

The d_slave service supports three different buffer locations:

• A transfer between a buffer in user memory and the device. With this type of transfer, the dp parameter specifies the cross-memory descriptor used with the xmattach service to attach to the kernel buffer. The baddr and count parameters must be the same values as the uaddr and count parameters specified to the xmattach service.
• A transfer between a global kernel memory buffer and the device. With this type of transfer, the dp->aspace_id variable has an XMEM_GLOBAL value.
• A transfer between I/O bus memory and the device. The BUS_DMA flag distinguishes this type of transfer from the other two types. The dp parameter is ignored with this type of transfer and should be set to null.

The d_unmask and d_mask services typically do not need to be called for the DMA slave transfers. The DMA channel is automatically enabled by the d_slave service and automatically disabled by the hardware when the last byte specified by the count parameter is transferred.

The d_slave service performs machine-dependent processing, including the following tasks:

• Flushing the processor cache
• Updating the referenced and changed bits of memory pages involved in the transfer
• Making the buffer inaccessible to the processor

  Notes:

  1. The memory buffer must remain pinned from the time the d_slave service is called until the DMA transfer is completed and the d_complete service is called.

  2. The device driver or device handler must not access the buffer once the d_slave service is called until the DMA transfer is completed and the d_complete service is called.

  3. The d_slave service, as with all DMA services, should not be called unless the DMA channel has been allocated with the d_init service.

Execution Environment

The d_slave kernel service can be called from either the process or interrupt environment.

Return Values

The d_slave service has no return values.

Implementation Specifics

The d_slave kernel service is part of Base Operating System (BOS) Runtime.

Related Information

The d_complete kernel service, d_init kernel service, d_mask kernel service, d_unmask kernel service, xmattach kernel service.

I/O Kernel Services and Understanding Direct Memory Access (DMA) Transfers in AIX Version 4.3 Kernel Extensions and Device Support Programming Concepts.