Pipelined processor with look-ahead mode of operation

Claim 2

Data processing apparatus comprising: (a) a plurality of pipeline stages connected in series, for executing a sequence of instructions in a pipelined manner, (b) control means connected to said pipeline stages and operative upon detection of a dependency between a first instruction and a second, subsequent instruction, for causing the second instruction to be abandoned, and for initiating a look-ahead mode of operation, (c) means connected to said pipeline stages and to said control means, and operative in the look-ahead mode, for allowing instructions subsequent to said second instruction to continue to be executed so as to prefetch any operands for those instructions, but not to be fully executed, and (d) means connected to said pipeline stages and to said control means, for terminating the look-ahead mode and returning to a normal mode of operation when said dependency is resolved, and for re-starting execution at said second instruction.

Claim 3

Apparatus according to claim 1 including means connected to said pipeline stages and to said control means, for terminating said look-ahead mode when said dependency is about to be resolved.

Claim 4

Apparatus according to claim 2 including a data slave store connected to said pipeline stages and means connected to said pipeline stages and to said control means, and operative to terminate the look-ahead mode when a data slave store access is initiated to retrieve data required for resolving the dependency, but before the data is actually available.

Claim 5

Apparatus according to claim 1, further including: (a) first counter means for indicating a next instruction to be started in normal mode, (b) second counter means for indicating a next instruction to be started in look-ahead mode, (c) means connected to the first and second counters and to said control means, for incrementing both counters in step with each other while the counters are equal in normal mode, (d) ;means connected to the second counter and to said control means, for incrementing only the second counter in look-ahead mode, and (e) means connected to the first counter and to said control means, and operative on return to normal mode for incrementing only the first counter, until said first counter is again equal to the second counter.

Claim 6

Apparatus according to claim 1, further including means connected to said pipeline stages, for initiating first and second independent streams of instructions, and means connected to said pipeline stages and to said control means, for placing each stream independently into said look-ahead mode.

Claim 7

Apparatus according to claim 5, including means connected to said control means and operative when one stream is in the look-ahead mode and the other is in the normal mode, for giving the stream in the normal mode execution priority over the other stream.

Claim 10

Data processing apparatus comprising: (a) a plurality of pipeline stages connected in series, for executing a sequence of instructions in a pipelined manner, (b) a data slave store, connected to the pipeline stages, for supplying operands for said instructions, (c) control means connected to said pipeline stages and operative upon detection of a dependency between a first instruction and a second, subsequent instruction, for causing the second instruction to be abandoned and for initiating a look-ahead mode of operation, (d) means connected to said pipeline stages and to said control means, and operative in the look-ahead mode, for allowing instructions subsequent to said second instruction to continue to be executed so as to prefetch any operands for said instructions into the data slave store, without allowing said instructions subsequent to said second instruction to be fully executed, and (e) means connected to said pipeline stages and to said control means, and operative when a data slave store access is initiated to retrieve data required for resolving said dependency, but before the data is actually available, to terminate the look-ahead mode, and to re-start execution at said second instruction.

Claim 11

Data processing apparatus comprising: (a) a plurality of pipeline stages connected in series, for executing a sequence of instructions in a pipelined manner, (b) a data slave store, connected to the pipeline stages, for supplying operands for said instructions, (c) control means connected to said pipeline stages and operative upon detection of a dependency between a first instruction and a second, subsequent instruction, for causing the second instruction to be abandoned and for initiating a look-ahead mode of operation, (d) means connected to said pipeline stages and to said control means, and operative in the look-ahead mode, for allowing instructions subsequent to said second instruction to continue to be executed so as to prefetch any operands for said instructions into the data slave store, without allowing said instructions subsequent to said second instruction to be fully executed, and (e) means connected to said pipeline stages and to said control means, and operative when a data slave store access is initiated to retrieve data required for resolving said dependency, but before the data is actually available, to terminate the look-ahead mode, and to re-start execution at said second instruction.