This chapter describes the SBSVmeAPI library.
This library supplies base functionality that allows applications to
access one or more VME crates on a local system via the SBS/Bit3/GE-Fanuc
fiber optic interface.
This chapter is divided as follows:
Provides a list of the classes, their purpose and intent.
Describes how to incorporate the headers and libraries into one of you applications.
The class library consists of the following classes that are considered public:
CVMEInterfaceProvides a thin class level wrapping around the set of SBS module operations that might exist for other types of VME interfaces
SBSBit3APIProvides a thin class level wrapping around the set of SBS module operations that are very likely SBS unique.
CVMEptrEncapsulates a VME address segment mapped into the process virtual address space in a pointer-like object. The pointer is reference counted so that it is well behaved in the presence of copy construction and asignment.
VmeModuleProvides base functionality that is intended to support classes that support a specific VME module.
To understand how to use these classes a quick overview of VME addressing may be useful. The VME bus has the following characteristics:
Up to 32 bits of address
Up to 32 bits of data
Address modifiers that provide several address spaces.
A discussion of the purpose and use of address modifiers is of the utmost importance. Bus cycles consist of address and data cycles. Each address cycle provides an address and an address modifier. Each data cycle provides a longword transfer and a set of data strobes that, for non-longword transfers, describe the set of bytes to be transferred at the address.
Address modifiers select which of several address spaces should be involved in data transfers associated with that address cycle. Three main address modifiers are the most important ones. These address modifiers are symbolically defined in the header file: CVMEInterface.h. They are:
Describes an address space that only pays attention to the bottom 16 bits of the address. Modules that recognize this space are intended to be I/O modules with a modest address space footprint. Modules in this address space can define their address maps to start on an 8 bit address boundary. This limits the bus to at most 256 short I/O address regions.
Describes an address space that only uses the bottom 24 bits of the address. This address space provides for a 16 bit data bus which is entirely located on the P1 (top) connector. In the past, this allowed for 3-U VME cards (1/2 height VME cards) to be built that fit in to a 1/2 heigbht backplane.
Describes an address space that uses the full 32 bits of VME addressing capability.
In addition to these addressing modes, the CVMEInterface::GEO, CVMEInterface::CBLT, and CVMEInterface::Multicast address modifiers provide symbolic names for the address modifier most often used by VME modules that implement these access modes. The VME64 standards provides an additional set of address modes that, by multiplexing the address and data lines on the backplane allow the same backplane to support 64 bit address and data spaces. The SBS controllers we have do not support these addressing modes.
Some address modifiers define high performance block transfer modes. In these data transfer modes, the address cycle only happens infrequently, followed by a burst of data cycles that are assumed to come from a sequential set of addresses. The SBS module can peform block transfers and transparently modifies the base address modifier you specify when a block transfer is performed.
See the reference pages for each of these classes for detailed information.