Index for Section 9

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dma_min_boundary(9r)
NAME
  dma_min_boundary - General: Returns system-level information

SYNOPSIS
  #include <io/common/devdriver.h>


  int dma_min_boundary(
	  struct controller *ctlr_p );

ARGUMENTS
  ctlr_p
      Specifies a pointer to the controller structure associated with this
      controller. The dma_min_boundary interface uses this pointer to obtain
      the system and bus-specific information needed to return the mask or
      integer value.

DESCRIPTION
  The dma_min_boundary interface returns an integer value that provides the
  information necessary for a device driver to determine the smallest DMA
  transfer that can be done atomically on a CPU or bus.	 The value returned
  by dma_min_boundary depends on the type of CPU or bus. For example, on a
  DEC 3000 Model 500 AXP Workstation connected to a TURBOchannel bus, this
  interface returns a value of 4. This indicates that a TURBOchannel DMA
  operation is atomic at the longword level (not the byte or word level). On
  a DEC 2000 Model 300 connected to an EISA bus, for example, this interface
  returns a value of 1 to indicate byte atomicity. Subbyte atomicity is not
  supported.

  On a DEC 3000 Model 500 AXP Workstation connected to a TURBOchannel bus,
  this return value of 4 informs a device driver about how to handle a DMA
  transfer that involves a buffer that begins and/or ends within a
  nonlongword aligned, nonintegral longword-sized (DMA) transfer. The device
  driver handles this DMA transfer by redirecting the beginning and/or end of
  the DMA transfer, respectively, to other buffers that must be merged to the
  main (aligned longword block) buffer through calls to bcopy.

RETURN VALUES
  The dma_min_boundary interface returns the value zero (0) to indicate that
  the system initialization code did not set up this field.  Otherwise,
  dma_min_boundary returns the byte-size atomicity value that the system
  supports for DMA operations for all controllers on the respective bus.







SEE ALSO
  Data Structures: controller(9s)

Index for Section 9

Alphabetical listing for D

Top of page