vb(7) [osf1 man page]

vb(7)							 Miscellaneous Information Manual						     vb(7)

NAME

       vb, sys_attrs_vme_vba - VMEbus backplane Ethernet interface

SYNOPSIS

       controller vb0 at vba0

DESCRIPTION

       The  VMEbus  backplane (vb) interface provides access to an Ethernet network through the VMEbus backplane driver, which acts as an Ethernet
       Datalink Layer driver.  This interface allows VMEbus-based systems to communicate directly over the VMEbus to other VMEbus-based systems on
       the same backplane, or on other Ethernet connected systems outside the backplane through a gateway node on the backplane.

       Both  the  Tru64  UNIX  and VxWorks for Alpha (Version 3.1 or higher) software support the vb driver as well as communication between these
       systems on the same backplane.  The Tru64 UNIX vb driver is supported on AXPvme and Alpha VME SBCs and Alpha VME 2100 systems.

       The VMEbus backplane interface requires you to modify the /etc/sysconfigtab file on your AXPvme or Alpha VME system in order  to  configure
       the  vb driver and to map VMEbus windows for the system.  Mapping the VMEbus windows on one node requires knowledge about every node in the
       vb network.

									  Note

       Do not modify any vme_vba kernel subsystem attributes.  To configure a vb network node, you modify attributes of the vb	driver	(vb:)  and
       the system's VMEbus adapter (vba_vipvic: or vba_univ:).

       See System Configuration Supplement: OEM Platforms for detailed information about the use of the vb interface on Alpha VME systems, includ-
       ing the following topics: VMEbus backplane (vb) network overview Configuring vb network nodes  Modifying  vb  driver  attributes  Modifying
       vba_vipvic adapter attributes Modifying vba_univ adapter attributes Examples Related ioctl commands Diagnostic messages Errors

RELATED INFORMATION

       Interfaces:  sys_attrs_vba_vipvic(7), sys_attrs_vba_univ(7), sysconfigdb(8)

       Network Administration, System Configuration Supplement: OEM Platforms delim off

																	     vb(7)

mb(9r)																	    mb(9r)

NAME

       mb - General: Performs a memory barrier

SYNOPSIS

       void mb(
	       void );

ARGUMENTS

       None

DESCRIPTION

       The Alpha architecture does not guarantee read/write ordering.  That is, the memory subsystem is free to complete read and write operations
       in any order that is optimal, without regard for the order in which they were  issued.  Read/write  ordering  is  not  the  same  as  cache
       coherency,  which  is  handled separately and is not an issue. The Alpha architecture also contains a write buffer (as do many high-perfor-
       mance RISC CPUs, including the MIPS R3000). This write buffer can coalesce multiple writes to identical or adjacent addresses into a single
       write,  effectively  losing earlier write requests.  Similarly, multiple reads to the same identical or adjacent addresses can be coalesced
       into a single read.

       This coalescing has implications for multiprocessor systems, as well as systems with off-board I/O or DMA engines that can read	or  modify
       memory asynchronously or that can require multiple writes to actually issue multiple data items. The mb (memory barrier) routine guarantees
       ordering of operations. The mb routine is derived from the MB instruction, which is described in the Alpha Architecture	Reference  Manual.
       The  mb	routine  is  a	superset of the wbflush routine that ULTRIX drivers use. For compatibility, wbflush is aliased to mb on Tru64 UNIX
       Alpha systems.

       You call mb in a device driver under the following circumstances: To force a barrier between load/store operations After the CPU  has  pre-
       pared  a  data  buffer in memory and before the device driver tries to perform a DMA out of the buffer Before attempting to read any device
       CSRs after taking a device interrupt Between writes

       Device drivers and the operating system are the primary users of the mb routine. However, some user programs, such as  a  graphics  program
       that  directly  maps  the  frame buffer and manipulates registers, might need to call mb. The operating system does not provide a C library
       routine for mb.	User programs that require use of mb should use the following asm construct:

       #include <c_asm.h>

       asm ("mb");

NOTES

       In most situations that would require a cache flush on other CPU architectures, you should call the mb routine on Tru64 UNIX Alpha systems.
       The  reason  is not that mb is equivalent to a cache flush (as it is not).  Rather, a common reason for doing a cache flush is to make data
       that the host CPU wrote available in main memory for access by the DMA device or to access from the host CPU data that was put in main mem-
       ory by a DMA device. In each case, on an Alpha CPU you should use a memory barrier to synchronize with that event.

       One example of using mb occurs with an Ethernet network controller. Each Ethernet network controller has a unique Ethernet hardware address
       that is typically contained in a ROM on the Ethernet controller board. The Ethernet hardware address is a multibyte sequence typically con-
       sisting	of  at	least  10  bytes. This multibyte Ethernet hardware address is frequently read from the controller hardware by the driver's
       probe routine by issuing a sequence of reads to the same controller register. Each successive read returns the next byte  of  the  Ethernet
       hardware  address.  In such instances, a call to mb should be inserted between each of these read operations to ensure that successive read
       operations are not coalesced into fewer actual reads as seen by the Ethernet controller.

RETURN VALUES

       None

																	    mb(9r)