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Method for adjusting fetch program counter in response to the number of instructions fetched and issued

  • US 5,708,788 A
  • Filed: 09/05/1995
  • Issued: 01/13/1998
  • Est. Priority Date: 03/03/1995
  • Status: Expired due to Term
First Claim
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1. A method of managing a clocked instruction flow subject to issue and fetch constraints in plurality of instruction latches which receive instructions, including, from selected memory locations, said method comprising the steps of:

  • checking whether a taken control transfer instruction is latched for issue;

    checking whether a taken control transfer instruction is fetched;

    checking whether a fetched taken control transfer instruction will not be in the next issue cycle;

    checking whether a taken control transfer instruction is latched for issue in the current cycle;

    determining the number of instructions fetched and the number of instructions issued in the current cycle;

    adjusting the fetch program counter in relationship to the number of issued instructions and the number of fetched instructions, if there is no taken control transfer instruction being fetched or latched for issue;

    adjusting the fetch program counter in relationship to the number of issued instructions and the number of fetched instructions, if no taken control transfer instruction is latched for issue, and a taken control transfer instruction is fetched, or a fetched taken control transfer instruction is not latched for issue;

    adjusting the fetch program counter to the target program counter of the first taken branch in the fetch cycle, if there is no taken control transfer instruction in the issue cycle, there is a predict taken branch in the fetch cycle, and there is a predict taken branch in the fetch cycle which will be loaded for issue;

    adjusting the fetch program counter to the target program counter of the first taken branch in the issue cycle, if there is a taken control transfer instruction in the issue cycle, and there is a predict taken branch latched for issue which will not be issued in this cycle;

    adjusting the fetch program counter to the current cycle fetch program count plus the fetch count, if there is a taken control transfer instruction in the issue cycle but not in the fetch cycle, and a taken control transfer instruction which will be latched for issue; and

    adjusting the fetch program counter to the target program counter of the first taken branch in the fetch cycle, if there is a taken control transfer instruction in the issue cycle and in the fetch cycle, and there is a taken control transfer instruction in the issue cycle which will be latched for issue in this cycle.

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