BSP Developer's Guide

4
Hardware Guidelines
Hardware Interrupts
Hardware bus interrupts are not used. Instead, messages are used to convey
information (such as device ready) or the actual I/O data. Message passing
provides a reliable and easily expandable means of sending information between
Multibus II agents. All backplane communications between agents can be handled
with messages. No master/slave memory interfaces are required – in fact, memory
interfaces are discouraged for use in communicating between boards. Because
messages contain data, a block of I/O data can be transferred in the same message
as the status or attention information. No memory addressing conflicts arise on the
bus and there are no bus memory caching problems because messages are sent
between agents, not memory addresses.
4
Processor Number
Initialization
Multibus boards are slot independent. At system initialization, the system
controller (slot 0) sends slot ID numbers to each board. The initialization software
on each board then sets up message IDs.
During initialization, any or all boards can use the interconnect space to locate
specific boards on the bus. For example, each device driver can search the bus for
boards that it “recognizes” and can control. This method allows board types and
locations and the system configuration to be determined at run time. Interconnect
registers and the data contained in interconnect records are defined by Intel.
Vendors who comply with the Intel specification identify themselves (via
interconnect data) as compliant. Non-compliant boards may be used; such boards
identify themselves as non-compliant.
Message Passing Protocol
Device Drivers
Intel has defined a transport protocol for use in sending messages; this protocol is
used by many board vendors. This makes adding new device devices easy because
the basic communication between agents uses existing message passing routines
and conventions. There is usually no hardware-specific code that needs to be
written to add a new device once the initial message-passing driver is in place.
A BSP normally includes one hardware device driver for the MPC chip (message
passing coprocessor) and a transport software module. All VxWorks I/O device
drivers send or receive messages by communicating on a software level with the
transport layer (or directly with the MPC driver, if necessary). The transport layer
75