Motorola MC68030 User Manual page 391

that provide the optimum performance for a given system. If the coprocessor
uses the synchronous bus interface all coprocessor signals and data must
be synchronized with the main processor clock. 80th the MC68881 and
MC68882 floating-point coprocessors use the asynchronous bus handshake
protocol.
The M68000 coprocessor interface also facilitates the design of coprocessors.
The coprocessor designer must only conform to the coprocessor interface
and does not need an extensive kn{)vyledge of the architecture of the main
processor. Also, the main processor can operate with a coprocessor without
having explicit provisions made in the main processor for the capabilities of
that coprocessor. This provides a great deal offreedom in the implementation
of a given coprocessor.
10.1.2 Concurrent Operation Support
The programmer's model for the M68000 Family of microprocessors is based
on sequential, nonconcurrent instruction execution. This implies that the
instructions in a given sequence must appear to be executed in the order in
which they occur. To maintain a uniform programmer's model, any copro-
cessor extensions should also maintain the model of sequential, noncon-
current instruction execution at the user level. Consequently, the programmer
can assume that the images of registers and memory affected by a given
instruction have been updated when the next instruction in the sequence
accessing these registers or memory locations is executed.
The M68000 coprocessor interface provides full support of all operations
necessary for nonconcurrent operation of the main processor and its asso-
ciated coprocessors. Although the M68000 coprocessor interface allows con-
currency in coprocessor execution, the coprocessor designer is responsible
for implementing this concurrency while maintaining
a
programming model
based on .sequential nonconcurrent instruction execution.
For example, if the coprocessor determines that instruction "8" does not use
or alter resources to be altered or used by instruction "A", instruction "8"
can be executed concurrently (if the executio,n hardware is also available).
Thus, the required instruction interdependencies and sequences of the pro-
gram are always respected. The MC68882 coprocessor offers concurrent in-
struction execution while the MC68881 coprocessor does not. However, the
MC68030 can execute instructions concurrently with coprocessor instruction
execution in the MC68881.
MOTOROLA
MC68030 USER'S MANUAL 10-3