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io_zero(9r)
NAME
  io_zero - General: Zeros a block of memory in bus address space

SYNOPSIS
  int io_zero(
	  io_handle_t destaddr,
	  u_long byte_count );

ARGUMENTS
  destaddr
      Specifies an I/O handle that you can use to reference a device register
      or memory located in bus address space (either I/O space or memory
      space). For io_zero, this I/O handle identifies the location in bus
      address space where the zero operation occurs. You can perform standard
      C mathematical operations (addition and subtraction only) on the I/O
      handle.  For example, you can add an offset to or subtract an offset
      from the I/O handle.

  byte_count
      Specifies the number of bytes in the data block to be zeroed.  The
      interface assumes that the buffer associated with the data block is
      physically contiguous.

DESCRIPTION
  The io_zero interface zeros byte_count bytes of memory beginning at the bus
  address specified by destaddr. The I/O handle you pass to destaddr
  identifies where the zero operation occurs in bus address space. The
  interface optimizes the copy operation for 32-bit transfers.

NOTES
  The io_zero interface is a generic interface that maps to a machine-
  specific interface that actually writes zeros to some location in bus
  address space. Using io_zero to perform the zero operation makes the device
  driver more portable across different CPU architectures and different CPU
  types within the same architecture.

CAUTIONS
  The I/O handle that you pass to the destaddr argument of the io_zero
  interface must be an I/O handle that references addresses residing in
  sparse space. All Alpha CPUs support sparse space. As a result, all bus
  configuration code should supply an I/O handle that references bus address
  space.

  If you pass an I/O handle to the destaddr argument that references
  addresses residing in some other space (for example, dense space) the
  results of the copy operation are unpredictable.

  Tru64 UNIX provides the following interfaces that allow device drivers to
  perform copy operations and zero blocks of memory on addresses that reside
  in dense space:

    ·  bcopy

       Copies a series of bytes with a specified limit

    ·  blkclr and bzero

       Zeros a block of memory

    ·  copyin

       Copies data from a user address space to a kernel address space

    ·  copyinstr

       Copies a null-terminated string from a user address space to a kernel
       address space

    ·  copyout

       Copies data from a kernel address space to a user address space

    ·  copyoutstr

       Copies a null-terminated string from a kernel address space to a user
       address space

RETURN VALUES
  Upon successful completion, io_zero returns IOA_OKAY. It returns the value
  -1 on failure.

SEE ALSO
  Kernel Interfaces: io_copyin(9r), io_copyio(9r), io_copyout(9r)

Index for Section 9

Alphabetical listing for I

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