Method and circuit for redefining bits in a control register

Details Method and circuit for redefining bits in a control register Method and circuit for redefining bits in a control register

1996-10-30

1999-05-11

Bowler, Alyssa H.

Boots, shoes, and leggings

395561, 364130, 36518907, G06F3/00;3/42;9/00

Patent

active

059037423

ABSTRACT:
A microprocessor includes a control register having a predetermined bit which is unconditionally writable to either a first state or a second state. Additional bits of the control register are writable to either the first or second state when the predetermined bit has the first state. Each additional bit is not writable when the predetermined bit has the second state. The microprocessor further includes at least one circuit controlled by the state of a corresponding one of the additional bits of the control register. The writability of the additional bits is preferably further conditioned upon the state of a machine status register, which is unconditionally writable to either the first state or the second state. A primary AND gate and a secondary AND gate corresponding to each additional bit control the writability of the additional bits. The secondary AND gates may further condition the writability of the corresponding additional bit on the state of a secondary machine status register, the current privilege level or other microprocessor status signals or plural additional inputs. Each bit of the control register is written into a corresponding bit of the shadow register upon writing the second state into the machine status register.

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patent: 5490267 (1996-02-01), Crosswy
patent: 5535404 (1996-07-01), Tsubota
patent: 5729760 (1998-03-01), Poisner

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